NCHurricane2009's Blog

2013 Atlantic Hurricane Season Birdseye Discussion #56

By: NCHurricane2009, 8:04 AM GMT on July 31, 2013

...WEDNESDAY JULY 31 2013 4:05 AM EDT...
Atlantic tropics remain quiet. June and July will have totaled four tropical cyclones in the Atlantic...which is an above average pace when compared to the 1966 to 2009 climatological data available on the National Hurricane Center site (http://www.nhc.noaa.gov/climo/images/cum-average_ Atl_1966-2009.gif).

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_31_2013_0315Z_zpsc1ee4d2f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_31_2013_0315Z_zpsc9ede541.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough is entering the upper-left corner of the above atmo chart from western Canada and the northwestern US. Eastern divergence of the upper shortwave supports surface 1004 mb frontal cyclone currently over NE Manitoba. Divergence ahead of the shortwave also supports 1014 mb frontal depression over Missouri developing along the lengthy front extending from 1012 mb frontal cyclone mentioned in paragraph P2 below.

P2...Upper trough previously over the NE US and eastern Canada is now transitioning into far eastern Canada and the NW Atlantic. Center of associated surface frontal cyclone...currently at 1012 mb...has moved from west-central Quebec and into the Gulf of St Lawrence between Nova Scotia and Newfoundland while supported by eastern divergence of the upper trough. Western convergence of the upper trough supports 1022 mb surface ridge over the eastern US. Low-level warm air southwest of the frontal cyclone supports southern US upper ridge...and low-level southerly warm air advection ahead of the frontal cyclone supports amplifying NW Atlantic upper anticyclone.

P3...Upper trough previously over the north-central Atlantic is moving into the NE Atlantic...with its eastern divergence supporting a deepening 1004 mb surface frontal low that has tracked from the waters NW of the Azores and into the waters offshore of western Europe in the last 24 hrs...and with its western convergence supporting a 1026 mb surface ridge that has moved from the east coast of Canada and southeastward into the open Atlantic while becoming the dominant center of P4 surface ridge.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1021 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 southern US upper ridge. The dominant open Atlantic center anchoring this ridge is transitioning to the 1026 mb center mentioned in paragraph P3 above.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex midway between the Lesser Antilles and Cape Verde Islands...mentioned in paragraph P6 of the previous discussion...has retrograded westward into the waters NE of the Lesser Antilles while moving around NW Atlantic upper anticyclone mentioned in paragraph P2. A surface trough is below supportive eastern divergence of this upper vortex...and this is the same surface trough mentioend in paragraph P3 of the previous discussion.

P6...Upper vortex settling into the Bahamas...mentioned in paragraph P5 of the previous discussion...has killed off the thunderstorm activity associated with the remnant tropical wave of Dorian as the remnant wave has slid below its suppressive upper convergence. The remnant tropical wave currently extends from the central Bahamas southward into the central Caribbean Sea...with the Caribbean portion of the tropical wave suppressed by paragraph P7 dry Saharan air as seen by brown shading in above thermo chart.

P7..The paragraph P5 and P6 upper vortices continue to split low-latitude upper ridging into one upper ridge over Central America...SE Mexico...and Caribbean Sea...a second upper anticyclone (upper ridge) just NE of the Caribbean Islands (and formerly supported by latent heat release back when Dorian had thunderstorms below it)...and a third upper anticyclone (upper ridge) in the eastern Atlantic extending into western Africa. South end of aforementioned upper anticyclone NE of the Caribbean Islands...in conjunction with the south end of the paragraph P4 surface ridge and south end of paragraph P2 NW Atlantic upper anticyclone...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Albeit their is some moistening coming in from the southeast associated with broad surface low pressure system emerging from western Africa mentioned in paragraph P10.

P8...Cluster of Central America thunderstorms...supported by outflow of paragraph P7 Central America-SE Mexico-Caribbean upper ridge have shifted westward into SE Mexico and into the eastern Pacific and therefore will no longer be mentioned on this blog which covers Atlantic activity.

P9...Tropical wave previously west and southwest of the Cape Verde Islands is moving into the waters midway between the Cape Verdes and Lesser Antilles while continuing to be suppressed by Saharan dry air mentioned in paragraph P7.

P10...At the time of the previous discussion a thunderstorm cluster was along the west coast of Africa almost to suggest a tropical wave was leaving the coast. However I did not mark it because their was also a gyre of cyclonic rotation observed further inland over the Mauritania/Mali border almost to suggest the gyre was the true axis of the suspect tropical wave. As of this time...the thunderstorm cluster on the west coast is now due south of the Cape Verde Islands with a secondary cyclonic gyre seen in the pararaph P7 saharan dry air just north of the thunderstorm cluster while the primary gyre is now over western Mauritania (with two gyres now observed do we have two instead of one tropical wave emerging from Africa?). Currently the NHC TAFB marks the secondary gyre as a 1012 mb surface low just west of the Cape Verde Islands and the primary gyre as a 1008 mb surface low over western Mauritania with a large northward kink in the ITCZ connecting the two.

2013 Atlantic Hurricane Season Birdseye Discussion #55

By: NCHurricane2009, 1:04 AM GMT on July 30, 2013

...MONDAY JULY 29 2013 9:05 PM EDT...
See paragraph P8 for update on remnant tropical wave of Tropical Storm Dorian. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_29_2013_2215Z_zps6cc10611.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1928Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_29_2013_2215Z_zps15c5922d.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper vortex previously over the Michigan lower peninsula is now an upper trough over the NE US and eastern Canada. Center of associated surface frontal cyclone...currently at 1011 mb...has moved from southeastern Ontario and into west-central Quebec while supported by eastern divergence of the upper trough. Western convergence of the upper trough supports 1023 mb surface ridge over the central and southeastern US. Low-level warm air southwest of the frontal cyclone supports SW US upper ridge mentioned in paragraph P2 of the previous discussion...and low-level warm air southeast of the frontal cyclone supports western of two north Atlantic upper anticyclones also mentioned in paragraph P2 of the previous discussion.

P2...Upper trough previously over the Nw Atlantic has moved into the north-central Atlantic...with its eastern divergence supporting a 1006 mb surface frontal low that has tracked from the waters just east of Newfoundland and into the waters NW of the Azores in the last 24 hrs...and with its western convergence supporting a 1025 mb surface ridge along the east coast of Canada. Low-level warmer air ahead of the 1006 mb frontal low supported eastern of two north Atlantic upper anticyclones mentioned at the end of paragraph P2 of the previous discussion...but now this upper anticyclone has merged with upper anticyclone north of the Cape Verde Islands mentioned in paragraph P6 below.

P3...Large NE Atlantic upper trough has finally moved into Europe (and exited the upper-right corner of the above charts) while knocking out deep-layered ridge over Europe associated with prior heat wave. Surface trough previously SW of the Canary Islands and NW of the Cape Verde Islands is now midway between the Lesser Antilles and Cape Verde Islands while retrograding westward around the south side of the paragraph P4 surface ridge. This surface trough was fracture from surface low previously supported by the exited NE Atlantic upper trough...and because of its current location I will move it to the tropical belt section in the next discussion if it still around by that time.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1020 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P1 SW US upper ridge. A 1025 mb center over Bermuda is supported by convergence between western of two North Atlantic upper anticyclones (mentioned in paragraph P1) and upper anticyclone over the remnants of Dorian. A 1022 mb center just west of Portugal is supported by western convergence of paragraph P3 upper trough.

P5...Upper vortex south of Bermuda is retrograding westward into the Bahamas while steered by western of the two north Atlantic upper anticyclones mentioned at the end of paragraph P1. At any time...the upper vortex will begin stalling over the Bahamas as further westward progression blocked by SW US upper ridge mentioned in paragraph P1.

...TROPICAL BELT DISCUSSION...
P6...Broad and retrograding upper vortex previously west of the Cape Verde Islands has arrived into the waters midway between the Lesser Antilles and Cape Verde Islands...and along with the paragraph P5 upper vortex south of Bermuda...has split low-latitude upper ridging into one upper anticyclone over Central America...a second upper anticyclone in the vicinity of the NE Caribbean Islands and over the remnants of Dorian...and a third upper anticyclone of the Cape Verde Islands and into western Africa. South end of aforementioned upper anticyclone in the vicinity of the NE Caribbean Islands...in conjunction with the south end of the paragraph P4 surface ridge and south end of paragraph P1 and P2 north Atlantic upper anticyclones...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Latent heat release of persistent central America thunderstorms has intensified paragraph P6 Central America upper anticyclone in the last 24 hrs...and in turn the increased outflow of the upper anticyclone has been re-enforcing the thunderstorms.

P8...Remnant tropical wave of Dorian earlier today continued to show signs of attempting to regenerate into a tropical storm due north of the Caribbean Islands while taking advantage of outflow of overhead upper anticyclone mentioned in paragrpah P6. While satellite imagery showed the thunderstorms become highly organized around a mid-level center and while reconnaissance aircraft indicated that this system continues to produce tropical storm force winds of about 40 mph...a closed surface circulation still could not be spotted and the lowest surface pressures are not collocated with the mid-level spin and therefore technically Dorian could not be re-classified as a tropical storm. As the remnant tropical wave moves toward the Bahamas during the next day or so...expect its activity and intensity to reduce while becoming suppressed by paragraph P5 upper vortex also settling into the Bahamas.

P9...Tropical wave west and southwest of the Cape Verde Islands continues proceeding westward while phased with suppressing retrograding upper vortex and Saharan dry air mentioned in paragraph P6.

2013 Atlantic Hurricane Season Birdseye Discussion #54

By: NCHurricane2009, 12:20 AM GMT on July 29, 2013

...SUNDAY JULY 28 2013 8:22 PM EDT...
Remnant tropical wave of Dorian has not regenerated into a tropical storm and will be entering less favorable upper winds below an upper vortex settling over the Bahamas. Therefore I have cancelled it as a special feature on this blog.

Elsewhere...activity along a decaying frontal boundary offshore of the United States east coast has diminished. Eastern Atlantic tropical wave is no longer a special feature on this blog while ingesting dry Saharan air.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_28_2013_1815Z_zpsd379c6e1.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1922Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_28_2013_1815Z_zps543918c3.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper vortex previously over Lake Michigan is now centered over the Michigan lower peninsula. Center of 1010 mb surface frontal cyclone has moved from Lake Superior and into southeastern Ontario while deepening to 1008 mb while supported by upper divergence between easterlies on the north side of the upper vortex and mainstream mid-latitude westerlies. Western convergence of upper vortex supports 1017 mb surface ridge over south-central Canada and central US.

P2...Upper trough previously over the Nw Atlantic...NE US...and far eastern Canada is now entirely in the NW Atlantic...with its eastern divergence supporting a 1008 mb surface frontal low that has tracked from Nova Scotia and into the waters just east of Newfoundland in the last 24 hrs...and with its western convergence supporting a 1023 mb surface ridge along the east coast of Canada. Northern fragment of this upper trough and associated less-than-1000 mb frontal cyclone previously moving across southern Greenland have mostly overtaken the NE Atlantic upper trough and surface low mentioned in paragraph P3 below. The front extending from the aforementioned 1008 mb low just east of Newfoundland was producing activity offshore of the eastern US that was monitored for tropical development during the previous discussion...but this is no longer the case as the cold front from the SE Ontario cyclone (paragraph P1) is overtaking this area (the only artifact left from this activity is the remnant 1013 mb low of disturbance Invest 90-L currently over eastern Massachusetts). Lastly...low-level warmer air ahead and south of the aforementioned SE Ontario frontal low...1008 mb frontal low east of Newfoundland...and less-than-1000 mb frontal low moving into the NE Atlantic...supports upper ridging over the SW US...northern Gulf of Mexico...and strong upper anticyclone over the north Atlantic which has recently split into two upper anticyclones due to the digging in of the NW Atlantic upper trough mentioned at the beginning of this paragraph.

P3...Large NE Atlantic upper trough is ever so slightly moving toward Europe while trying to defeat deep-layered ridge over Europe. The surface low pressure center formerly supported by eastern divergence of this upper trough has finally moved NE into the British Isles...but has become absorbed by the front of the less-than-1000 mb cyclone mentioned in paragraph P2. What is left of the absorbed surface low pressure system is a western Europe front marked in the upper-right corner of the above atmo chart and a surface trough SW of the Canary Islands and NW of the Cape Verde Islands that is beginning to retrograde westward around the south side of the paragraph P4 surface ridge.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1018 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge has weakened to 1026 mb and shifted west while transitioning to being supported by SE convergence of the western of the two north Atlantic upper anticyclcones mentioned at the end of paragraph P2.

P5...Upper vortex south of Bermuda is retrograding westward into the Bahamas while steered by western of the two north Atlantic upper anticyclones mentioned at the end of paragraph P2. In the next 24 hrs...the upper vortex will begin stalling over the Bahamas as further westward progression blocked by SW US and northern Gulf of Mexico upper ridge mentioned in paragraph P2.

...TROPICAL BELT DISCUSSION...
P6...Broad and retrograding upper vortex west of the Cape Verde Islands...along with the paragraph P5 upper vortex south of Bermuda...has split low-latitude upper ridging into one upper anticyclone over Central America...a second upper anticyclone in the vicinity of the Lesser Antilles and over the remnants of Dorian...and a third upper ridge north of the Cape Verde Islands and into western Africa. South end of aforementioned upper anticyclone in the vicinity of the Lesser Antilles...in conjunction with the south end of the paragraph P4 surface ridge and south end of paragraph P2 north Atlantic upper anticyclones...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Area of south-central Caribbean thunderstorms mentioned in paragraph P7 of the previous discussion has transitioned into Central America while associated with the outflow of Central America upper anticyclone.

P8...Remnant tropical wave of Dorian earlier today showed signs of attempting to regenerate into a tropical storm due north of the Lesser Antilles while taking advantage of outflow of Lesser Antilles area upper anticyclone mentioned in paragrpah P6. While reconnaissance aircraft indicated that this system continues to produce tropical storm force winds of about 40 mph...a closed surface circulation could not be spotted and therefore technically Dorian could not be re-classified as a tropical storm. As the remnant tropical wave moves toward the Bahamas during the next day or so...expect its activity and intensity to reduce while becoming suppressed by paragraph P5 upper vortex also settling into the Bahamas.

P9...Tropical wave axis previously over and south of the Cape Verde Islands is now west and southwest of the islands. The previous and organizing thunderstorm cluster east of the wave axis enhanced by outflow of paragraph P6 upper ridge in the vicinity of the Cape Verde Islands extending into W Africa seemed to have potential to develop while the upper ridge was expected to expand in the wake of the broad and retrograding upper vortex mentioned at the beginning of paragraph P6. Now that this thunderstorm cluster has diminished...this tropical wave is no longer interesting and therefore is no longer a special feature on this blog. Tropical wave axis will proceed westward while phased with suppressing retrograding upper vortex and Saharan dry air mentioned in paragraph P6.

2013 Atlantic Hurricane Season Birdseye Discussion #53A (Special Update)

By: NCHurricane2009, 9:30 PM GMT on July 27, 2013

...SATURDAY JULY 27 2013 5:30 PM EDT...
A satellite scan of surface winds has revealed that Dorian's surface circulation has opened up into a tropical wave...and therefore despite maintaining 40 mph maximum sustained winds Dorian is technically no longer a tropical storm. Therefore the National Hurricane Center (NHC) has stopped advisories on Tropical Storm Dorian unless regeneration of a closed surface circulation occurs. I believe the highest chance of any regeneration potential is between now and Monday morning...after which time the remnant tropical wave of Dorian will slide under an upper vortex stalling over the Bahamas and dissipate below its upper convergence.

I still stand behind the intensity forecast shown in Figure 1 of full discussion #53...which suggests that the remnant tropical wave of Dorian could maintain 40 mph maximum sustained winds between now and Monday morning. Interpret the track forecast line as the projected track of the lowest surface pressure along Dorian's remnant tropical wave.

Return to full discussion #53 for an assessment on the rest of the Atlantic tropics...including in depth discussion of disturbed weather offshore of the eastern United States associated with a decaying frontal boundary and an eastern Atlantic tropical wave that has become better organized this afternoon. Should the system offshore of the eastern United States quickly develop during the next 24 hours...I will be posting additional special updates between now and my next full discussion...

2013 Atlantic Hurricane Season Birdseye Discussion #53

By: NCHurricane2009, 9:10 PM GMT on July 27, 2013

...SATURDAY JULY 27 2013 5:10 PM EDT...
Dorian likely to dissipate as it approaches the Bahamas in the next 72 hours. See Dorian special feature section below for additional details.

Elsewhere...Atlantic tropical activity has increased within the last 24 hours. Watching a decaying frontal boundary offshore of the eastern United States coast...see second special feature section for details. Also watching a vigorous tropical wave emerging from Africa...see third special feature section below for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_27_2013_1345Z_zps4bc19a59.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1329Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_27_2013_1345Z_zpsc5d1c38f.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM DORIAN...
As expected...Dorian has slid under the Lesser Antilles area upper anticyclone which is helping Dorian by keeping shear low and enhancing upper outflow. Despite this...Dorian's thunderstorms have struggled to make a comeback such that he remains at an equilibrium strength of about 40 mph maximum sustained winds perhaps as the paragraph P6 Saharan dry air has become too much for him. Therefore my updated intensity forecast in Figure 1 below no longer shows re-strengthening under the upper anticyclone. The next obstacle for Dorian is upper vortex south of Bermuda which will retrograde west in the next 48 hrs and then stall over the Bahamas afterwards (see paragraph P5 for more details). Therefore Dorian will enter a light southerly shear environment on the west side of the upper anticyclone and east side of the retrograding upper vortex between now and 48 hrs...an environment I assume will not be hostile enough such that Dorian chugs along while maintaining 40 mph max winds. Then as the upper vortex stalls over Bahamas by 72 hrs...I expect he will dissipate in the upper convergence below the upper vortex.

Thru the forecast period...the track of Dorian should be steady to the west-northwest with models agreeing on firm surface ridging persisting to the north. The heading of Dorian did bend a bit more west (as the NHC predicted and I did not) between the previous discussion and now...perhaps as Dorian could no longer make anymore northward progress against the strong paragraph P4 surface ridge center. However the most recent segment of NHC recorded storm track in Figure 1 when studied carefully shows a northward deflection re-developing as this surface ridge center begins weakening (while shifting west) as described in detail in paragraph P4. Because of that deflection I maintain the same forecast track line I had previously shown...which has a slight north bias relative to NHC. Regarding forward pace...Dorian has moved a bit faster than the previous forecast showed...so my updated forecast points along my forecast track in Figure 1 are basically the same as previous except that I have moved them a bit more forward. These forecast points still show that Dorian will gradually slow down a bit as the paragraph P4 surface ridge weakens thru the forecast period.

 photo Jul_27_2013_TS_Dorian_Forecast_zpsf72bc4ff.png
Figure 1: My forecast versus the NHC's 11 AM EDT forecast for Tropical Storm Dorian

Impact swath in Figure 1 is extrapolation of Dorian's compact tropical storm wind field along my forecast track...then dissipating the wind field when I think Dorian will weaken below tropical storm (40+ mph) force. Statement about surf and rip currents has been cancelled because Dorian is expected to be a weak to dissipating ciruclation during the forecast period.

...SPECIAL FEATURE...DECAYING FRONTAL BOUDNARY OFFSHORE OF THE EASTERN UNITED STATES INCLUDING SURFACE LOW INVEST 90-L...
Decaying frontal boundary offshore of the eastern United States...mentioned in paragraph P2 in the mid-latitudes section below...has developed three areas of disturbed weather.

The first is a large thunderstorm cluster northeast of Bermuda. As the end of paragraph P2 mentioned...a large upper anticyclone east-southeast of Newfoundland is splitting into two..and this thunderstorm cluster is the result of upper outflow of the western of the two upper anticyclones. Because this thunderstorm cluster is located in the midst of high surface pressures on the west side of paragraph P4 1031 mb ridge center...I do not expect tropical cyclone formation from this system.

The second area of disturbed weather...a weak frontal boundary low...began developing yesterday afternoon due east of Florida due to eastern divergence of paragraph P2 upper trough. While tracking NNE parallel to the eastern United States shore (due to the west side of paragraph P4 1031 mb ridge)...this surface low has developed a circular thunderstorm cluster while passing east of the North Carolina outer banks...and as a result was promplty upgraded to disturbance Invest 90-L and introduced into the NHC tropical weather outlook this afternoon. Expect during its remaining life for the surface low to track NNE while continuing to be steered by west side of 1031 mb ridge and then west side of the paragraph P2 1026 mb ridge. In the next 24 hrs its current NNE track will keep this surface low south of the 26 deg C water temp isotherm such that tropical cyclone formation risk is high...especially as the surface low in the later part of the next 24 hrs may take advantage of low shear and enhanced upper outflow as the western of the two upper anticyclones ESE of Newfoundland expands behind the paragraph P2 upper trough lifting off to the northeast. Between 24 and 48 hrs conditions for tropical cyclone development will be hostile as the surface low enters waters below 26 deg C and as it gets absorbed by paragraph P1 1010 mb cyclone's cold front. At worst...we could be talking about a tropical depression with brief rain and gusty winds for the coast of Massachusetts 24 hours from now...with the system diminishing while moving into Nova Scotia between 24 and 48 hrs.

The third area of disturbed weather is another weak frontal boundary low east of Florida whose thunderstorms have increased this afternoon due to the outflow at the east end of northern Gulf of Mexico upper ridge mentioned in paragraph P2. Between now and 24 hrs as this surface low tracks NNE to a position offshore of the Carolinas (while steered by west side of paragraph P4 1031 mb surface ridge)...tropical development risk appears decent as low shear and enhanced upper anticyclonic outflow will continue in the region offshore of the eastern US behind the paragraph P2 upper trough lifting off to the northeast. After 24 hrs...tropical cyclone development risk should drop off quickly as the paragraph P1 1010 mb cyclone's cold front coming in from the west absorbs this surface low.

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
In paragraph P8 of the previous discussion...I was expecting the tropical wave that has recently emerged from Africa would become suppressed by retrograding upper vortex currently centered NW of the Cape Verde Islands and mentioned in paragraph P6. The tropical wave axis is currently located over and south of the Cape Verde Islands such that it indeed still appears phased to be suppressed by the retrograding upper vortex. However...it appears eastern convergence of the tropical wave supports an area of thunderstorms southeast of the Cape Verde Islands and just offshore of Africa that has become better organized this afternoon under the enhanced outflow and low shear of W Africa/Cape Verde Islands upper anticyclone mentioned in paragraph P6. And with this upper anticyclone progged to expand westward in the wake of the retorgrading upper vortex...I believe their is now a decent chance of tropical development. In the event this system begins choking on Saharan dry air mentioned in paragraph P6...then I will cancel it as a special feature.

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and associated 1010 mb surface frontal low has dove southeast from south-central Canada and into the Great Lakes and eastern Canada region in the northwesterly flow behind the paragraph P2 upper trough. The upper trough has closed off into an upper vortex currently centered over southern Lake Michigan while the 1010 mb surface center is just north of Lake Superior. Western convergence of the upper vortex supports 1026 mb surface ridge centered over the North Dakota/Canada border.

P2...Upper trough has translated from the eastern Canada/Great Lakes region and into the NW Atlantic...NE US...and far eastern Cananda. A northern fragment of the upper trough has split off while crossing Greenland...with the fragment's eastern upper divergence supporting 998 mb surface frontal cyclone and fragment's western upper convergence of this fragment supports 1026 mb SSW of Greenland. Along the front extending from the 998 mb cyclone is a relatively new 1009 mb surface low that has tracked from offshore of North Carolina and into Nova Scotia in the last 36 hrs (this surface low is supported by eastern divergence of aforementioned NW Atlantic/NE US upper trough). Remainder of the front is decaying into 1012 mb frontal depression centered over northern Louisiana that is becoming supported by eastern divergence of paragraph P1 upper vortex and into features offshore of the eastern US that have gained some tropical characteristics in the last 36 hrs...see above second special feature section for details. Lastly...low-level warmer air ahead and south of the aforementioned 1012 mb...1009 mb...and 998 mb frontal lows cold fronts supports upper ridging over the SW US...northern Gulf of Mexico...and strong upper anticyclone centered ESE of Newfoundland. The strong upper anticyclone ESE of Newfoundland is beginning to split into two due to the digging in of aforementioned NW Atlantic/NE US upper trough.

P3...Large NE Atlantic upper trough is ever so slightly moving toward Europe while trying to defeat deep-layered ridge over Europe. The surface low pressure center formerly supported by eastern divergence of this upper trough has weakened to 994 mb while now quasi-stationary below the non-divergent axis of the upper trough itself.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1017 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge has weakened to 1031 mb while becoming vertically stacked with paragraph P2 upper anticyclone ESE of Newfoundland. As the end of paragraph P2 mentions...this upper anticyclone is starting to split into two anticyclones. Expect in the short term for this 1031 mb ridge center to continue weakening and shifting west while transitioning to being supported by SE convergence of the western of the two upper anticyclones.

P5...Upper vortex persists south of Bermuda. Expect this upper vortex between now and 48 hrs to retrograde west into the Bahamas while steered by western of the two upper anticyclones mentioned at the end of paragraph P4. The upper vortex will then stall over the Bahamas by 72 hrs with further westward progression blocked by SW US and northern Gulf of Mexico upper ridge mentioned in paragraph P2.

...TROPICAL BELT DISCUSSION...
P6...South end of paragraph P3 NE Atlantic upper trough has split off into a broad upper vortex NW of the Cape Verde Islands that will begin retrograding west about the paragraph P2 upper anticyclone ESE of Newfoundland. This upper vortex...along with the paragraph P5 upper vortex south of Bermuda...has split low-latitude upper ridging into one upper anticyclone over the southern Caribbean...a second upper anticyclone in the vicinity of the Lesser Antilles and over Tropical storm Dorian...and a third upper anticyclone over the Cape Verde Islands and into western Africa. South end of aforementioned upper anticyclone in the vicinity of the Lesser Antilles...in conjunction with the south end of the paragraph P4 surface ridge and south end of paragraph P2 upper anticyclone ESE of Newfoundland...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. This Saharan dry air is mitigated in the vicinity of tropical storm Dorian and also the eastern Atlantic tropical wave mentioned in the above third special feature section.

P7...Tropical wave previously over SE Mexico and Central America has moved into the eastern Pacific. Area of south-central Caribbean thunderstorms that may have been kick-started by eastern convergence of this tropical wave during the previous discussion persist in split flow upper divergence between easterlies across the south side of paragraph P6 south Caribbean upper anticyclone and westerlies across the south side of the paragraph P5 upper vortex south of Bermuda.

P8...Tropical wave rolling off of Africa in paragraph P8 of the previous discussion has been moved to above third special feature section.

2013 Atlantic Hurricane Season Birdseye Discussion #52

By: NCHurricane2009, 10:30 AM GMT on July 26, 2013

...FRIDAY JULY 26 2013 6:30 AM EDT...
Dorian's window to become a hurricane appears to have closed for now as the storm struggles in a dry air environment. The storm could find a more favorable environment while passing north of the Caribbean Islands...then once again weaken while approaching the Bahamas early next week. See Dorian special feature section for details.

As expected...disturbance Invest 99-L northeast of Bermuda has diminished in an environment of high surface pressures.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_25_2013_2345Z_zps8d70e356.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0129Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_25_2013_2345Z_zps9212311a.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM DORIAN...
After reaching a peak strength of 60 mph winds yesterday...Dorian has weakened to 50 mph maximum winds overnight. My previous expectation was that Dorian's upper anticyclone would have enough thunderstorm latent heat release behind it such that the anticyclone would push out unfavorable mid-ocean upper vorticity mentioned in paragraph P6 to the degree that it would merge with paragraph P5 upper vortex south of Bermuda...afterwards the anticyclone pushing out that upper vortex as Dorian strengthened further into a hurricane. Instead it appears the mid-ocean upper vorticity could no longer be pushed westward and away as the vorticity became stopped up by paragraph P6 upper anticyclone in the vicinity of the Lesser Antilles...and now Dorian has crashed into the upper vorticity and left its upper anticyclone behind to the east. This has allowed the thunderstorms supported by the outflow of the anticyclone to lag behind to the east such that the Saharan dry air mentioned in paragraph P6 has worked it way into the west side of the circulation. Based on studying the 5-day upper wind forecast from the 00Z GFS...my updated intensity forecast in Figure 1 shows Dorian weakening further in the next 24 hours while passing below the unfavorable mid-ocean upper vorticity...then Dorian recovering below the favorable upper outflow of Lesser Antilles upper anticyclone by 48 and 72 hrs...then the storm struggling again by 96 hrs while encountering the paragraph P5 upper vortex south of Bermuda...then the storm recovering again by 120 hrs as it escapes the upper vortex.

Thru the forecast period...the track of Dorian should be steady to the west-northwest with models agreeing on firm surface ridging persisting to the north. I was previously south of the NHC as their recorded storm track showed an early bend to the west coupled with the fact that the paragraph P4 surface ridge to the north was strengthening. Instead that turned out to be a westward wobble which was later smoothed out in the NHC recorded storm track...and now looking at the NHC recorded storm track we see a general line that could be extrapolated WNW toward the eastern and central Bahamas by day 5...so my updated forecast track in Figure 1 is a northward shift from the previous. The recent NHC forecast tracks have wanted to show a westward bend toward the southern Bahamas apparenty due to the paragraph P4 surface ridge shifting to the west (this west shift will occur as the north lobe of paragraph P5 upper vortex and paragraph P2 upper trough fragment merge in the north Atlnatic...splitting the upper anticyclone ESE of Newfoundland into two anticyclones...and the west shift is due to the surface ridge transitioning to being supported by SE convergence of the western upper anticyclone). The reason I instead develop a northward bias more toward the central Bahamas by day 5 is because the westward-shifting surface ridge is also shown in models to be gradually weaker from currently levels...so I prefer extrapolating the current WNW heading all the way rather than NHC's westward bend. Regarding forward pace...I have slowed down a bit from my previous and now am more aligned with the NHC (but NHC and I are still faster than the GFS computer model). This is because the 24-hour width between the NHC's forecast points matches pretty well with the 24-hour distance Dorian covered between 11 PM EDT Wednesday and 11 PM EDT overnight. After 48 hrs...the 24-hour widths on NHC forecast track narrows while showing a slower storm. I agree with some slow down between 48 and 72 hrs based on the GFS showing a weaker surface ridge to the north by that time...but then I show a faster pace than NHC between 72 and 96 hrs with the GFS showing the surface ridge maintaining strength...then slow my forecast further between 96 and 120 hrs as the GFS shows the surface ridging due north being a little more weaker. By 120 hrs...it should be noted that the convergent west side of the pargraph P1 upper trough will extend the west side of the paragraph P4 surface ridge into the southeastern US...so a northward bend toward the US east coast or offshore of the US east coast in the very long range appears unlikely.

 photo Jul_26_2013_TS_Dorian_Forecast_zps25ae2aa6.png
Figure 1: My forecast versus the NHC's 11 PM EDT forecast for Tropical Storm Dorian

Impact swath in Figure 1 is extrapolation of Dorian's compact tropical storm wind field along my forecast track with the assumption that the storm does not grow in size or appreciably strengthen thru the forecast period.

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and associated 1011 mb surface frontal low is diving southeast from south-central Canada in the northwesterly flow behind the paragraph P2 upper trough.

P2...Upper trough persists across the Great Lakes and eastern Canada. Its eastern divergence supports surface frontal cyclone fluctuating between 1000 and 999 mb in the last 24 hrs while tracking from eastern Canada and into the waters between Canada and Greenland. Western convergence of this upper trough supports 1021 mb ridge over the New York/Canada border. Low-level warmer air ahead and south of the frontal cyclone's cold fronts supports upper ridging over the SW US...northern Gulf of Mexico...and strong upper anticyclone centered ESE of Newfoundland.

P3...Large NE Atlantic upper trough is ever so slightly moving toward Europe while trying to defeat deep-layered ridge over Europe. The surface low pressure center supported by eastern divergence of this upper trough was moving toward the British Isles while deepening in the low 990s in mb..then made a cyclonic loop below the vorticity of the upper trough axis. Now that it is directly below the non-divergent upper trough axis...expect this surface low to generally weaken.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1019 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge has reached a peak of 1035 mb under the southeastern convergence of paragraph P2 upper anticyclone ESE of Newfoundland...but now the upper anticylcone and surface ridge will orbit anticyclonically about each other and become vertically stacked such that the surface ridge will begin a slow weakening.

P5...Upper vortex persists south of Bermuda...with split flow upper divergence between northeasterlies on the northwest half of the upper vortex and southerlies on the west side of the paragraph P2 upper anticyclone ESE of Newfoundland continuing to support an area of thunderstorms east and northeast of Bermuda. The weak surface low of disturbance Invest 99-L embedded in these thunderstorms has been in and out of NHC TAFB surface mapping...and for now appears to have permanently dissipated as of the 0000Z TAFB map due to the high surface pressures of paragraph P4 surface ridge center to the east which has strengthened to 1035 mb in the last 24 hrs.

...TROPICAL BELT DISCUSSION...
P6...Low-latitude upper ridge covering the tropical Atlantic remains split into one upper anticyclone over Tropical Storm Dorian...and another upper anticyclone in the vicinity of the Lesser Antilles which has recently undergone a westward expansion into the southern Caribbean in the wake of the weakening western Caribbean upper trough mentioned in paragraph P7 of the previous discussion. Large-scale mid-ocean upper vorticity between the two aforementioned upper anticyclones persists...and currently this upper vorticity is what is causing Dorian to struggle (see above Dorian special feature section for more details). South end of aforementioned Lesser Antilles upper anticyclone...in conjunction with the south end of the paragraph P4 surface ridge and south end of paragraph P2 upper anticyclone ESE of Newfoundland...was advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. This Saharan dry air mass continues shrinking due to the moisture surge associated with Tropical Storm Dorian coming in from the east.

P7...Tropical wave previously over the western Caribbean is moving into SE Mexico and across Central America. It remains suppressed by sinking dry air associated with southern convergence of northern Gulf of Mexico upper ridge mentioned in paragraph P2. Just to the southeast of the tropical wave is an increased area of thunderstorms over the south-central Caribbean associated with enhanced poleward upper outflow of west lobe of Lesser Antilles-area upper anticyclone which as mentioned in paragraph P6 above has expanded into the southern Caribbean. It is also possible these thunderstorms were kick-started by eastern convergence of this tropical wave.

P8...Next tropical wave appears to be rolling off of Africa as marked in the lower-right corner of the above atmo chart. Although Dorian far to the west has moistened up the environment ahead of the tropical wave...this tropical wave does not look as impressive as the pre-Dorian wave did...and furthermore expect this tropical wave to become suppressed by southern fracture of paragraph P3 upper trough currently developing to the east of Dorian's upper anticyclone.

2013 Atlantic Hurricane Season Birdseye Discussion #51

By: NCHurricane2009, 6:32 AM GMT on July 25, 2013

...THURSDAY JULY 25 2013 2:33 AM EDT...
As highlighted in special updates #50A and #50B...vigorous eastern Atlantic tropical wave has intensified into Tropical Storm Dorian. It appears Dorian has the potential to become the season's first hurricane...and as such interests in the Lesser Antilles...Virgin Islands...Puerto Rico...Haiti...the Dominican Republic..and the Bahamas should monitor this situation carefully as the storm approaches the region this weekend into early next week. See Dorian special feature section below for additional details.

A disturbance has developed east of Bermuda...designated as Invest 99-L by the Naval Research Laboratory and introduced into the National Hurricane Center Tropical Weather Outlook within the last 24 hours. Due to high surface pressures in the area...I do not expect tropical cyclone formation from this system as it track generally northward toward the Atlantic Canada shores of Nova Scotia and Newfoundland during the next three days. See paragraph P6 for additional details on this disturbance.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_24_2013_2345Z_zps54e53324.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_24_2013_2345Z_zps0da7c2b3.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM DORIAN...
Tropical Storm Dorian continues churning west-northwestward while currently at a location well west of the Cape Verde Islands. Despite tracking over 25 to 26 deg C waters...the storm does not appear to be weakening to 45 mph maximum winds as I predicted it would during special update #50B released this past afternoon. This could be due to the southern low-level inflow staying in touch with the warmer air above the warmer waters to the south as the NHC 11 AM EDT advisory discussion suggested yesterday morning. In fact the fairly recent 11 PM EDT NHC advisory suggested Dorian may be strengthening to 60 mph winds due to the slightly improved appearance of its central storm core...and I expect that the storm will be upgraded to such strength later this morning. Animation of water vapor imagery shows Dorian's surface convergence (coupled with the upper divergence associated with its upper anticyclone) producing a robust moisture field that is driving out the adjacent Saharan dry air mass mentioned in paragraph P7. Moreover...some of the latest computer model guidance shows the favorable upper anticyclone staying coupled over Dorian thru the forecast period. Previously models suggested that Dorian's upper anticyclone would not have enough t-storm latent heat release behind it such that Dorian would later run into what is now the less favorable mid-ocean upper vorticity mentioned in paragraph P7. An illustration of a computer model that recently switched over to showing Dorian's upper anticyclone staying coupled is shown in Figure 1. Putting all the above pieces together...my latest intensity forecast in Figure 2 is well above the NHC intensity guidance...showing Dorian being a high-end category 1 hurricane by the end of day 5. I flatten my intensification rate towards the end of my forecast due to land interaction with Puerto Rico and Hispaniola...and also out of conservativeness in case I am wrong in predicitng Dorian to reach hurricane strength.

 photo Jul_24_2013_300mb_GFS_for_Dorian_zps9cfc8d75.png
Figure 1: GFS computer model run predictions for the upper air (300 mb) wind pattern for July 31 0000Z. Black arrows are added to help show the predicted wind directions from the wind barbs. Screenshot (a) is associated with tonight's 18Z model run while screenshot (b) is associated with last night's 18Z model run. Last night's GFS model run showed Dorian on July 31 as a much weaker system becoming suppressed by upper vorticity shown in orange shading. Tonight's model run is initialized with a stronger Dorian such that by July 31 it now shows less upper vorticity (less orange shading) and more favorable upper anticyclonic outflow over Dorian as shown by the black arrows in frame (a). Due to current signs of Dorian doing well...I am extrapolating that it will be a strong tropical cyclone in the days leading to July 31 such that I lean with the solution shown in frame (a).

Thru the forecast period...the track of Dorian will be controlled by paragraph P6 surface ridge. This surface ridge is predicted to strengthen in the next 24 hrs due to surface convergence of paragraph P2 upper anticyclone SE of Newfoundland...after which time it becomes vertically stacked with the upper anticyclone and begins weakening. Recent segment of NHC recorded storm track in Figure 2 shows Dorian has bent more westward in track already...so I predict in the next 24 hrs the track will bend even more west due to the strengthening surface ridge such that I am south of the NHC track guidance. I then bend my forecast track more WNW later on based on when models show the surface ridge weakening. My forward pace is also a bit ahead of the NHC track and GFS computer model as I extrapolated the 12-hourly forward pace from 11 AM yesterday morning (when Dorian was at 30W) to 11 PM EDT earlier this evening.

 photo Jul_25_2013_TS_Dorian_Forecast_zps1e92e43b.png
Figure 2: My forecast versus the NHC's 11 PM EDT forecast for Tropical Storm Dorian

Impact swath in Figure 2 is extrapolation of Dorian's compact tropical storm wind field along my forecast track. I gradually grow the size of the swath to reflect my predicted strengthening. Interests in the Lesser Antilles...Virgin Islands...Puerto Rico...Haiti...the Dominican Republic..and the Bahamas should monitor this situation carefully as the storm approaches the region this weekend into early next week. For the Lesser Antilles...it appears likely the northern islands have the highest chance for tropical storm (or possibly hurricane) conditions...while the southern Lesesr Antilles would only experience surf and or rip currents along the coast.

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and associated 1011 mb surface frontal low is diving southeast from south-central Canada in the northwesterly flow behind the paragraph P2 upper trough.

P2...Upper trough persists across the Great Lakes and eastern Canada. Its eastern divergence supports surface frontal cyclone that has deepened from 1003 to 1000 mb in the last 24 hrs while tracking from the NE US and into eastern Canada. Western convergence of this upper trough supports 1018 mb ridge over the Great Lakes. Low-level warmer air ahead and south of the absorbing 1000 mb frontal cyclone's cold fronts supports upper ridging over the SW US...northern Gulf of Mexico...and strong upper anticyclone centered SE of Newfoundland.

P3...Large NE Atlantic upper trough remains stationary as its eastward progression is blocked by deep-layered ridge over Europe. At the surface...1003 mb center sliding northeast toward the British Isles is supported by eastern divergence of the upper trough. Western convergence of the upper trough meanwhile supports 1026 to 1030 mb surface ridging from the south tip of Greenland and into the Azores.

P5...Surface ridge dominates much of the open Atlantic basin...with a current westward 1016 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge is supported by southeastern convergence of paragraph P2 upper anticyclone SE of Newfoundland.

P6...As paragraph P7 of previous discussion #50 mentioned...it appeared the vertical contrast between sea-surface temps of 27 to 28 deg C and cold temps of an open central Atlantic upper vortex supported thunderstorms east of Bermuda. Paragraph P7 of previous discussion #50 also mentioned an upper vortex south of Bermuda. It appeared yesterday afternoon that these thunderstorms became moreso maintained by split flow upper divergence at the boundary between these two upper vortices...with this upper divergence also supporting the formation of a weak surface low in the midst of the paragraph P5 surface ridge. As the two upper vortices have merged...it now appears these thunderstorms are supported by split flow upper divergence between easterlies north of the merged upper vortex and southerlies west of the paragraph P2 upper anticyclone SE of Newfoundland. This area of disturbed weather...designated as Invest 99-L...has favorable conditions of waters greater than 26 deg C...low shear due to deep-layered flow around the paragraph P5 surface ridge and paragraph P2 upper anticyclone SE of Newfoundland...and in fact it may get enhanced upper anticyclonic outflow on the west lobe of this anticyclone. Despite all of this...I don't think will develop further due to high surface pressures of paragraph P5 surface ridge...and in fact the surface low of this disturbance was recently cancelled in 0000Z NHC TAFB mapping. Regardless of development...this disturbance over the next two to three days will take a curving north and then east path toward the Atlantic Canada shores of Nova Scotia and Newfoundland while buried in the deep-layered flow around the west and north sides of aforementioned surface ridge and upper anticyclone.

...TROPICAL BELT DISCUSSION...
P7...Low-latitude upper ridge covering the eastern tropical Atlantic remains split into one upper anticyclone over Tropical Storm Dorian...while the other upper anticyclone previously over northern Lesser Antilles has been de-amplified southward into the southern Lesser Antilles thanks to the merged upper vortex associated with disturbance Invest 99-L mentioned in paragraph P6. Large-scale mid-ocean upper vorticity between the two upper anticyclones persists. Upper ridge over Central America persists...while the central Caribbean upper trough has retrograded westward into the western Caribbean while steered by northern Gulf upper ridge mentioned in paragraph P2. South end of aforementioned Lesser Antilles upper anticyclone...in conjunction with the south end of the paragraph P6 surface ridge and south end of paragraph P2 upper anticyclone SE of Newfoundland...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Albeit this Saharan dry air mass has recently shrunken due to the moisture surge associated with Tropical Storm Dorian coming in from the east.

P8...Tropical wave previously over Hispaniola (Haiti and the Dominican Republic) is moving into Central America and the western Caribbean. It is suppressed by sinking dry air associated with southeastern convergence of northern Gulf of Mexico upper ridge mentioned in paragraph P2.

2013 Atlantic Hurricane Season Birdseye Discussion #50B (Special Update)

By: NCHurricane2009, 3:30 PM GMT on July 24, 2013

...WEDNESDAY JULY 24 2013 11:35 AM EDT...
Tropical depression four has strengthend to Tropical Storm Dorian as of 11 AM EDT...centered 410 miles west-southwest of the Cape Verde Islands. This event has occured while the storm core of the circulation remained robust over 26 to 27 deg C waters. Based on the current WNW heading of the Dorian...between now and 5 AM tomorrow morning...the system will be crossing sea-surface temperatures at or below 26 deg C...which I predict will cause the thunderstorm activity to weaken from this morning's levels and thus allow a chance of Saharan dry air to get ingested into the circulation from the northwest. Therefore I am still below the latest NHC intensity guidance while I forecast some weakening of the storm between now and 5 AM tomorrow morning:

11 AM Wed Jul 24 2013..50 mph...initial
5 PM Wed Jul 24 2013...50 mph...6 hr
5 AM Thu Jul 25 2013...45 mph...18 hr

I will be doing a full forecast for this tropical cyclone in my next discussion tonight. In the meantime refer to the National Hurricane Center (www.nhc.noaa.gov) for latest information on this system. Return to full discussion #50 for an assessment on the rest of the Atlantic tropics.

2013 Atlantic Hurricane Season Birdseye Discussion #50A (Special Update)

By: NCHurricane2009, 11:10 AM GMT on July 24, 2013

...WEDNESDAY JULY 24 2013 6:45 AM EDT...
Tropical wave Invest 98-L has become tropical depression four as of 5 AM EDT this morning...centered 310 miles west-southwest of the Cape Verde Islands. Based on the current WNW heading of the depression...between now and 5 AM tomorrow morning...the system will be crossing sea-surface temperatures at or below 26 deg C...which will keep the thunderstorm activity on the weaker side and thus allow a chance of Saharan dry air to get ingested into the circulation from the northwest. Therefore I forecast a bit of a slower intensification rate than the NHC did at 5 AM:

5 AM Wed Jul 24 2013..35 mph...initial
5 PM Wed Jul 24 2013...35 mph...12 hr
5 AM Thu Jul 25 2013...40 mph...24 hr

I will be doing a full forecast for this tropical cyclone in my next discussion tonight. In the meantime refer to the National Hurricane Center (www.nhc.noaa.gov) for latest information on this system. Return to full discussion #50 for an assessment on the rest of the Atlantic tropics.

2013 Atlantic Hurricane Season Birdseye Discussion #50

By: NCHurricane2009, 12:47 AM GMT on July 24, 2013

...TUESDAY JULY 23 2013 8:47 PM EDT...
High probability of a tropical cyclone this week in the waters between the Cape Verde Islands and Lesser Antilles from vigorous tropical wave that has become better organized in the eastern tropical Atlantic. See special feature section below for additional details. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_23_2013_2045Z_zps4c55ebf3.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_23_2013_2045Z_zpsc12170af.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE INVEST 98-L...
While taking advantage of low shear and enhanced upper outflow associated with its own upper anticyclone mentioned in paragraph P7...the vigorous eastern Atlantic tropical wave has organized into a surface low pressure spin while passing south of the Cape Verde Islands during the last 24 hours. As this has occurred...it appears the north half of the system is struggling to develop thunderstorms due to adjacent Saharan dry air mass mentioned in paragraph P7. The thunderstorms are also lopsided a bit to the west due to easterly shear caused by the fact that the upper anticyclone is just north of rather than directly over the system...but additional thunderstorm latent heat release could cause the upper anticyclone to build directly overhead and later on reduce the easterly shear. Additional uncertainty lies ahead...with the tropical wave soon to track toward a pool of cooler waters at and below 26 deg C located due west of the Cape Verde Islands as seen in the above thermo chart. This pool could mean low enough atmospheric instability during the next 24 hours such that the thunderstorms relax...and if this occurs the Saharan dry air has a chance of killing off tropical cyclogensis altogether. On the other hand...this system is so close to becoming a tropical cyclone I would rather not cancel it as a special feature on this blog. Plus the computer models continue to show the favorable upper anticyclone staying with this system even after passing by the cool water pool and into richly warmer waters...so tropical cyclone formation could still occur later on if it doesn't become one right before the passage thru the cooler water pool.

Marine interests in the Atlantic tropical waters between the Cape Verde Islands and the Lesser Antilles should monitor the progress of this tropical wave over the next few days as it gets steered generally westward by deep-layered easterlies south of the paragraph P6 surface ridge and paragraph P2 north-central Atlantic upper ridge. Even though the paragraph P7 mid-ocean upper vorticity will retrograde westward while getting pushed by this tropical system's upper anticyclone and south side of paragraph P2 north-central Atlantic upper ridge...longer-range computer model runs suggest this tropical wave will eventually catch up to the unfavorable environment of the upper vorticity as it nears the Lesser Antilles. However interests in the Lesser Antilles should still keep a wary eye on this tropical system until further notice.

...MID-LATITUDES DISCUSSION...
P1...Upper trough previously over the central US and central Canada is pushing across the Great Lakes and eastern Canada. Its eastern divergence formerly supported 996 mb surface frontal cyclone currently just south of Hudson Bay that has now become stacked with the non-divergent upper trough axis. Eastern divergence of the upper trough now supports new 1003 mb depression currently over the NE US that will gradually assume dominance while the 996 mb center begins decay. Western convergence of this upper trough supports 1019 mb ridge building over the north-central US and south-central Canada.

P2...Upper trough previously over eastern Canada has merged with NE Atlantic upper trough mentioned in paragraph P3. Surface 990 mb frontal cyclone over eastern Canada has become absorbed by north side of 996 mb cyclone mentioned in paragraph P1. Low-level warmer air ahead and south of the absorbing 996 mb surface frontal cyclone's cold fronts supports upper ridging over the SW US...northern Gulf of Mexico...the waters offshore of the eastern US...and into the north-central Atlantic.

P3...Large NE Atlantic upper trough remains stationary as its eastward progression is blocked by deep-layered ridge over Europe. At the surface...the surface 1005 mb center previously moving toward the British Isles of Europe has become replaced by new 1004 mb center also moving NE toward the British Isles. This 1004 mb center has developed along the occluded front of the absorbed paragraph P2 990 mb cyclone while supported by eastern divergence of the upper trough. Western convergence of the upper trough meanwhile supports 1021 mb ridge east of Newfoundland.

P4...What is left of east-west surface troughing in the open Atlantic...formerly supported by divergence between easterlies south of the paragraph P2 north-central Atlnatic upper ridge and mainstream mid-latitude westerlies...is now a dissipating 1019 mb surface low west of the Canary Islands and south of the Azores.

P5...Upper vortex persists over the Bay of Campeche.

P6...Surface ridge dominates much of the open Atlantic basin...with a current westward extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge is supported by southeastern convergence of paragraph P2 north-central Atlantic upper ridge (as well as paragraph P2 upper ridging offshore of eastern US) and western convergence of paragraph P7 upper vortex south of Bermuda.

...TROPICAL BELT DISCUSSION...
P7...Low-latitude upper ridge covering the eastern tropical Atlantic remains split into one upper anitcyclone centered over the northern Lesser Antilles and another upper anticyclone associated with the t-storm latent heat release of tropical wave Invest 98-L...with large-scale mid-ocean upper vorticity between the two upper anticyclones. Southern Caribbean t-storms mentioned in paragraph P8 of the previous discussion have moved into Nicaragua and Honduras...with the associated latent heat release continuing to support upper ridge over Central America (central Caribbean upper trough persists between the Central America upper ridge and northern Lesser Antilles upper anticyclone). Low-level warm air advection ahead of paragraph P1 996 mb cyclone has intensified paragraph P2 upper ridging offshore of the eastern US such that the upper vortex previously SW of Bermuda has been pushed eastward to the waters south of Bermuda. South end of aforementioned northern Lesser Antilles upper anticyclone...in conjunction with the south end of the paragraph P6 surface ridge and south end of paragraph P2 north-central Atlantic upper ridge...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Open central Atlantic upper vortex continues retrograding westward around the paragraph P2 north-central Atlantic upper ridge...and while over sea-surface temps in the 27 to 28 deg C range it appears the vertical contrast between the warm waters and cold air of the upper vortex continues to support instability and t-storms east of Bermuda.

P8...Tropical wave previously over Puerto Rico is now over Hispaniola (Haiti and the Dominican Republic). Its thunderstorm activity has declined while moving below oppressive and non-divergent upper atmosphere due south of the paragraph P7 upper vortex south of Bermuda.

2013 Atlantic Hurricane Season Birdseye Discussion #49

By: NCHurricane2009, 2:14 AM GMT on July 23, 2013

...MONDAY JULY 22 2013 10:15 PM EDT...
High probablity of a tropical cyclone this week in the waters between the Cape Verde Islands and Lesser Antilles from vigorous tropical wave that has emerged from Africa. See special feature section below for additional details. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_22_2013_1845Z_zps6d834393.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1925Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_22_2013_1845Z_zps302aee3b.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE INVEST 98-L...
Impressive tropical wave with organized thunderstorm activity has emerged from the west coast of Africa and into the tropical waters SE of the Cape Verde Islands as seen in the lower-right corner of the above atmo chart. The tropical wave is in a favorable atmoshperic environment of low shear and enhanced upper outflow due to the development of its own upper anticyclone within the large-scale low-latitude upper ridge covering the eastern tropical Atlantic mentioned in paragraph P7. Over the last three days...the GFS and CMC computer models have shown development potential from this tropical wave while generally suggesting this tropical wave will continue to maintain this upper anticyclone...and even the conservative Euro (ECMWF) model has joined the bandwagon in the last 24 hrs. And because the surface convergence of the tropical wave...coupled with the upper divergence of the upper anitcyclone...has created a large enough moisture field that is warding off the dry Saharan air layer to the northwest (mentioned in paragraph P7)...this system has a high risk of becoming an Atlantic tropical cyclone...which is why I upgraded it to a special feature as of special update #48A earlier this afternoon.

Marine interests in the Atlantic tropical waters between the Cape Verde Islands and the Lesser Antilles should monitor the progress of this tropical wave over the next few days as it gets steered generally westward by deep-layered easterlies south of the paragraph P6 surface ridge and paragraph P2 north-central Atlantic upper ridge. Even though the paragraph P7 upper vortex midway between the Lesser Antilles and Cape Verde Islands will retrograde westward while getting pushed by this tropical wave's upper anticyclone and south side of paragraph P2 north-central Atlantic upper ridge...longer-range computer model runs suggest this tropical wave will eventually catch up to the unfavorable environment of the upper vortex as it nears the Lesser Antilles. However interests in the Lesser Antilles should also keep a wary eye on this tropical wave.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough in the mid-latitude westerlies has entered the upper-left corner of the above charts and is currently positioned over central Canada and the central US. Its eastern divergence supports 999 mb surface frontal cyclone just SW of Hudson Bay.

P2...Upper trough and associated 990 mb surface frontal cyclone persists over eastern Canada. Low-level warmer air ahead and south of the 990 mb surface frontal cyclone's cold fronts (in addition to the warmer air south of the 999 mb cyclone mentioned in paragraph P1) supports upper ridge over the SW US...another upper ridge over the eastern Gulf of Mexico that has recently expanded into the waters offshore of the SE US...and also the persistent upper ridge in the north-central Atlantic.

P3...Large NE Atlantic upper trough remains stationary as its eastward progression is blocked by deep-layered ridge over Europe. At the surface...the dominant feature below this upper trough is an intensfying 1005 mb center that is taking advantage of the eastern divergence of this upper trough while it moves NE toward the British Isles.

P4...East-west surface troughing in the open central Atlantic...mentioned in paragraph P3 of the previous discussion...currently persists south of the Azores and west of the Canary Islands while generally supported by split flow upper divergence between easterlies southeast of the north-central Atlantic upper ridge mentioned in paragraph P2 and mainstream mid-latitude westerlies.

P5...SE US to western Gulf of Mexico upper trough mentioned in paragraph P4 of the previous discussion has largely been absorbed by the south end of the paragraph P1 upper trough. What has not been absorbed is currently an upper vortex over the Bay of Campeche.

P6...Surface ridge dominates much of the open Atlantic basin...with a current westward extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge is supported by southeastern convergence of paragraph P2 north-central Atlantic upper ridge and western convergence of paragraph P7 upper trough SW of Bermuda.

...TROPICAL BELT DISCUSSION...
P7...Low-latitude upper ridge covering the eastern tropical Atlantic has split into one upper anitcyclone centered over the northern Lesser Antilles and another upper anticyclone associated with the t-storm latent heat release of tropical wave Invest 98-L...with inverted upper trough midway between the Lesser Antilles and Cape Verde Islands (mentioned in paragraph P6 of the previous discusison) evolving into an upper vortex between the two upper anticyclones. Due to latent heat release of southern Caribbean thunderstorms mentioned in paragraph P8...Central America upper vortex has been pushed back east into the central Caribbean as a weakened upper trough while an upper ridge has flared up over SE Mexico and Central America. Upper trough persists SW of Bermuda. South end of aforementioned northern Lesser Antilles upper anticyclone...in conjunction with the south end of the paragraph P6 surface ridge and south end of paragraph P2 north-central Atlantic upper anticyclone...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Open central Atlantic upper vortex continues retrograding westward around the paragraph P2 north-central Atlantic upper ridge...and as it moves toward sea-surface temps greater than 28 deg C (as indicated by above thermo chart) it appears the vertical contrast between the warm waters and cold air of the upper vortex has supported an increase in instability and t-storms east of Bermuda.

P8...Thundestorm activity in the southern Caribbean persists while supported by split flow upper divergence between westerlies flowing across south side of paragrpah P7 Central Caribbean upper trough and easterlies flowing across south side of paragraph P7 Central America upper ridge. Pop-up t-storm clusters continue east of Florida and offshore of SE US due to outflow of eastern Gulf of Mexico upper ridge mentioned in paragraph P2. Thunderstorm activity along the US Gulf coast is supported by split flow upper divergence at the boundary between paragraph P2 SW US upper ridge and paragraph P2 eastern Gulf of Mexico upper ridge.

P9...Tropical wave previously moving toward the Lesser Antilles has crossed the islands and into Puerto Rico. Now that it has escaped the stream of Saharan dry air mentioned in paragraph P7...its thunderstorms have increased due to outflow of northern Lesser Antilles upper anticyclone also mentioned in paragraph P7.

2013 Atlantic Hurricane Season Birdseye Discussion #48A (Special Update)

By: NCHurricane2009, 8:22 PM GMT on July 22, 2013

...MONDAY JULY 22 2013 4:22 PM EDT...
Vigorous tropical wave emerging from Africa during the previous discussion is holding its own against the Saharan dry air to its north and west. The tropical wave has also been upgraded to disturbance Invest 98-L. Because I believe this tropical wave has a high risk of eventually becoming an Atlantic tropical cyclone...I am now considering it a special feature. Therefore this tropical wave will receive its own special feature section in my next blog post later tonight. Marine interests in the Atlantic tropical waters between the Cape Verde Islands and the Lesser Antilles should monitor the progress of this tropical wave over the next few days.

Return to full discussion #48 for an assessment on the rest of the Atlnatic tropics.

2013 Atlantic Hurricane Season Birdseye Discussion #48

By: NCHurricane2009, 7:04 PM GMT on July 21, 2013

...SUNDAY JULY 21 2013 3:04 PM EDT...
Monitoring a vigorous tropical wave emerging from the west coast of Africa. See paragraph P10 for details. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_21_2013_1215Z_zpsc42e5b1f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_21_2013_1215Z_zpsfa2fccf2.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper trough and associated surface frontal cyclone persists over eastern Canada. The surface cyclone has weakened from 990 to 994 mb in last 24 hrs while stationary below non-divergent upper trough axis...while eastern divergence of the upper trough supports 992 mb depression on the east Canada coast. Western convergence of the amplified upper trough supports 1018 mb ridge over the Great Lakes. Low-level warmer air ahead of the surface frontal cyclone's cold fronts supports upper ridge over the SW US...another upper ridge over the eastern Gulf of Mexico (merger of SE US upper ridge mentioned in paragraph P1 of the previous discussion and upper ridge over western Cuba mentioned in paragraph P7 of the previous discussion)...and upper ridge that has moved from the NW Atlantic into the north-central Atlantic.

P2...Deep-layered vortex south of Greenland (paragraph P2 of the previous discussion)...deep-layered vortex just SE of Greenland (paragraph P3 of the previous discussion)...and deep-layered vortex NW of Spain (paragraph P3 of the previous discussion)...have merged into a large NE Atlantic upper trough whose further eastward progression is blocked by deep-layered ridge over Europe mentioned in paragraph P3 of the previous discussion. At the surface...the dominant feature below the NE Atlantic upper trough is a less-than-1008 mb center associated with what was the deep-layered vortex south of Greenland.

P3...Lengthy east-west surface troughing in the open central Atlantic...mentioned in paragraph P4 of the previous discussion...currently persists while generally supported by split flow upper divergence between easterlies southeast of the north-central Atlantic upper ridge mentioned in paragraph P1 and mainstream mid-latitude westerlies. This surface troughing wraps all the way into less-than-1008 mb surface center mentioned in paragraph P2.

P4...Louisiana upper vortex has weakened into an upper trough spanning the SE US and western Gulf of Mexico.

P5...Surface ridge dominates much of the open Atlantic basin...with a current westward extension into the Gulf of Mexico. Much of the open Atlantic portion of this surface ridge is supported by southeastern convergence of paragraph P1 north-central Atlantic upper ridge and western convergence of paragraph P6 upper trough SW of Bermuda.

...TROPICAL BELT DISCUSSION...
P6...Prominent low-latitude upper ridge axis continues covering the eastern tropical Atlantic and eastern Caribbean. Strong tropical wave emerging from Africa...mentioned in paragraph P10...has upper anticyclone pumped up by its thunderstorm latent heat release...with relatively lower pressures between the anticyclone and main body of the low-latitude upper ridge supporting new inverted upper trough midway between the Lesser Antilles and Cape Verde Islands. Upper vortex previously in the central Caribbean is retrograding westward into Central America while moving around the south side of eastern Gulf of Mexico upper ridge mentioned in paragraph P1. Upper vortex SW of Bermuda has weakened into upper trough. South end of aforementioned low-latitude upper ridge axis...in conjunction with the south end of the paragraph P5 surface ridge...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Open central Atlantic upper vortex continues retrograding westward around the paragraph P1 north-central Atlantic upper ridge.

P7...Tropical wave previously over SE Mexico has moved into the eastern Pacific while becoming better organized into tropical disturbance Invest 98-E. Because this blog does not cover eastern Pacific activity...this is my final mention of this tropical wave.

P8...Tropical wave previously moving into Central America was dropped from NHC TAFB surface maps as of 0600Z this morning. However an impressive flare-up of t-storms in the southern Caribbean...also covering Panama and Costa Rica...may have been triggered by the surface convergence of this dissipating tropical wave...and these t-storms also appear to be supported by split flow upper divergence between westerlies flowing across south side of paragrpah P6 Central America upper vortex and low-latitude tropical upper easterlies. Although the north fragment of this tropical wave was removed over the Bahamas during the previous discussion...pop-up t-storm clusters continue in the vicinity...mainly east of Florida...due to upper outflow of eastern Gulf of Mexico upper ridge mentioned in paragraph P1.

P9...Tropical wave continues moving toward the Lesser Antilles. It is entirely suppressed by dry Saharan air mentioned in paragraph P6.

P10...Impressive tropical wave with organized thunderstorm activity is about to emerge from the west coast of Africa and into the Atlantic tropics as seen in the lower-right corner of the above atmo chart. The tropical wave is entering a favorable atmoshperic environment of low shear and enhanced upper outflow due to the development of its own upper anticyclone within the large-scale low-latitude upper ridge covering the eastern tropical Atlantic mentioned in paragraph P6. Over the last couple of days...the GFS and CMC computer models show development potential from this tropical wave while generally suggesting this tropical wave will continue to maintain this upper anticyclone. Given all of this...I will not be upgrading this tropical wave to a special feature on this blog until I see how well it fares against the Saharan dry air mentioned in paragraph P6.

2013 Atlantic Hurricane Season Birdseye Discussion #47

By: NCHurricane2009, 6:14 PM GMT on July 20, 2013

...SATURDAY JULY 20 2013 2:15 PM EDT...
Tropical wave has moved from Haiti and into the western Caribbean and Bahamas region since the previous discussion. Their are no signs of development as it moved into favorable upper winds...see paragraph P10 for details.

Thunderstorm activity over the central Gulf of Mexico continues to be associated with surface troughing mentioned in paragraph P8 interacting with upper divergence around a Louisiana upper vortex mentioned in paragraph P5. This area was introduced into the National Hurricane Center Tropical Weather Outlook yesterday afternoon and is now being canncelled from the outlook due to lack of persistence in the thunderstorms.

I have inspected the Naval Research Laboratory site of the US Navy and found that their is no Invest number assigned to the above-mentioned Gulf activity. However in their archives I found that the short-lived western Gulf of Mexico activity that occured on July 17 early morning (paragraph P6 of discussion #44) was breifly classified as Invest 97-L even though that activity was never introduced into the National Hurricane Center Tropical Weather Outlook. This info was not conveyed on this blog earlier...so I thought I would mention it now.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_20_2013_1215Z_zps7e133cc8.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_20_2013_1215Z_zps9a73d8aa.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough previously over central Canada has become more amplified while moving into eastern Canada thanks to cool air advection on back side of surface frontal depression that has also moved from central to eastern Canada in last 36 hrs while intensifying from 998 to 990 mb (the intensification of surface frontal depression was in turn due to eastern divergence of amplifying upper trough). Western convergence of the amplified upper trough supports building surface ridge over central Canada. Low-level warmer air ahead of the surface frontal depression's cold fronts supports upper ridge over the SW US...another upper ridge over the SE US...and upper ridge that has moved from the eastern US (mentioned in paragraph P4 of the previous discussion) and into the NW Atlnatic.

P2...Upper trough and associated surface frontal cyclone previously between Canada and Greenland has evolved into deep-layered vortex of less-than-1004 mb due south of Greenland. Western upper-level convergence of the deep-layered vortex supports 1020 mb surface ridge east of Newfoundland.

P3...Upper trough persists SE of Greenland...extending now into the Canary Islands. 1005 mb frontal depression north of the Azores...mentioned in paragraph P4 of the previous discussion...has moved NNW to the waters just SE of Greenland while rounding the west side of deep-layered ridging consisting of Europe upper ridge and Europe fracture of paragraph P6 surface ridge. This surface frontal depression is currently just below 1008 mb and is also deep-layered while aligning with upper vorticity of the upper trough. Eastern divergence of the upper trough supports new 1012 mb frontal depression NW of Spain that has also recently become deep-layered while aligning with the upper vorticity of the upper trough. Finally...western convergence of this upper trough supports 1019 mb surface ridge currently just NE of the Azores.

P4...Lengthy east-west surface troughing in the open central Atlantic...mentioned in paragraph P4 of the previous discussion...currently persists while generally supported by split flow upper divergence between easterlies southeast of the NW Atlantic upper ridge mentioned in paragraph P1 and mainstream mid-latitude westerlies. This surface troughing wraps all the way into 1012 mb frontal depression NW of Spain mentioned in paragraph P3.

P5...North-central Gulf of Mexico upper vortex has moved NW into Lousiana while moving about SE US upper ridge mentioned in paragraph P1.

P6...Surface ridge dominates much of the open Atlantic basin...with a current westward extension onto the US Gulf coast. The open Atlantic portion of this surface ridge is supported by southeastern convergence of paragraph P1 NW Atlantic upper ridge. The Europe portion of this surface ridge has fractured from the main open Atlnatic portion thanks to the digging in of paragraph P3 and P2 upper vorticity and surface frontal depression features.

...TROPICAL BELT DISCUSSION...
P7...Prominent low-latitude upper ridge axis continues covering the eastern tropical Atlantic and eastern Caribbean. Upper vortex previously in the eastern Caribbean has retrograded further west into the central Caribbean as an inverted upper trough while steered around paragraph P1 NW Atlantic upper ridge...and upper vortex previously south of Bermuda is now SW of Bermuda while also steered around paragraph P1 NW Atlantic upper ridge...with both of these upper vortices continuing to seperate the aforementioned low-latitude upper ridge axis from the Caribbean portion of low-latitude upper ridging. The Caribbean portion of low-latitude upper ridging has recently consolidated as a western Cuba upper anticyclone in the widening gap between the paragraph P5 upper vortex and upper vortex SW of Bermuda mentioned earlier in this paragraph. South end of all the low-latitude upper ridging in this paragraph...in conjunction with the south end of the paragraph P6 surface ridge...is also advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Lastly...the north-central Atlantic upper anticyclone mentioned in paragraph P7 of the previous discusison has become absorbed by paragraph P1 NW Atlnatic upper anticyclone...but the new upper vortex in the open central Atlantic due south of the absorbed upper anticyclone is beginning to retrograde south and west about the paragraph P1 NW Atlantic upper anticyclone.

P8...Central Gulf of Mexico surface trough mentioned in paragraph P8 of the previous discussion has recently dissipated...but thunderstorms that have been pulsing up and down in intensity continue to be supported by eastern divergence of paragraph P5 upper vortex currently centered over Louisiana. These thunderstorms were impressive enough yesterday afternoon for the National Hurricane Center to mentioned this area in their tropical weather outlook...but now this area has been removed from their outlook as of this afternoon.

P9...Tropical wave previously moving into Central America is now over SE Mexico and the Bay of Campeche. It is largely inactive while suppressed by westerly shear and lack of upper divergence due south of the Louisiana upper vortex mentioned in paragraph P5.

P10...Tropical wave previously over Haiti developed a northern fracture moving into the Bahamas 36 hrs ago that has just been cancelled as of the 1200Z NHC TAFB surface mapping. Remainder of this tropical wave is currently moving toward Central America and the western Caribbean. Previous prognosis was to watch this tropical wave as it slides below favorable low shear and enhanced upper outflow environment of what is now the western Cuba upper anticyclone mentioned in paragraph P7. Atlhough their are some pop-up thunderstorm clusters supported by this upper outflow environment...they are not impressive enough to suggest tropical cyclone development from this tropical wave...and computer models continue to show no development here.

P11...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles is moving toward the Lesser Antilles. It is entirely suppressed by dry Saharan air mentioned in paragraph P7.

2013 Atlantic Hurricane Season Birdseye Discussion #46

By: NCHurricane2009, 11:13 AM GMT on July 19, 2013

...FRIDAY JULY 19 2013 7:15 AM EDT...
Watching tropical wave currently over Haiti expected to move into favorable upper winds over the next 48 hours. See paragraph P10 for details.

Thunderstorm activity over the Yucatan...southeast Gulf of Mexico...and Florida yesterday afternoon was associated with surface troughing mentioned in paragraph P8 interacting with upper divergence around a north-central Gulf of Mexico upper vortex mentioned in paragraph P5. As these thunderstorms have died down as of this morning...no tropical or subtropical development is expected.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_19_2013_0545Z_zps725e3146.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0720Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_19_2013_0545Z_zps168c4fd9.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough is entering the upper-left corner of the above charts. Western convergence of the shortwave supports 1019 mb surface ridge over eastern Montana...eastern divergence of the shortwave supports broad 998 mb surface frontal depression over south-central Canada.

P2...Upper trough and associated surface 994 mb frontal cyclone continues east from eastern Canada and into the Atlantic high seas between Canada and Greenland (eastern divergence of this upper trough also supports new 1004 mb depression east of Newfoundland). Western convergence of the upper trough supports 1016 mb surface ridge between Nova Scotia and Newfoundland.

P3...Upper trough persists SSE of Greenland...with eastern divergence of the upper trough supporting a surface frontal cyclone that has moved northward and out of the picture while rounding the west side of deep-layered ridging consisting of upper ridge mentioned further down this paragraph and the western Europe portion of paragraph P6 surface ridge. Western convergence of this upper trough supports 1021 mb surface ridge currently just NW of the Azores. Warm air advection ahead of the exited frontal cyclone supports building upper ridge that has moved into the British Isles of western Europe.

P4...Cut-off upper vortex previously over New Mexico continues retrograding westward into NW Mexico and out of the picture while retrograding about the south side of a western US upper ridge. Surface troughing extending from the shores of the US mid-Atlnatic states eastward into the open central Atlantic for several hundred miles...mentioned in paragraph P3 of the previous discussion...currently persists while generally supported by split flow upper divergence between easterlies southeast of the eastern US upper ridge (pumped up by low-level warm air advection on west side of paragraph P6 surface ridge) and mainstream mid-latitude westerlies. This surface troughing wraps all the way into 1005 mb frontal depression north of the Azores supported by eastern divergence of paragraph P3 upper trough.

P5...Cut-off upper vortex previously north of the Azores is now a northeastward moving upper trough west of Portugal and Spain as it moves around the British Isles upper ridge mentioned at the end of paragraph P3. A southwest portion of this upper vorticity several days ago has evolved into what is now the upper vortex moving into the north-central Gulf of Mexico that continues retrograding westward about the eastern US upper ridge mentioned in paragraph P4.

P6...Surface ridge dominates much of the open Atlantic basin...with a current westward extension onto the US Gulf coast. The US Gulf coast and open Atlantic portion of this surface ridge is supported by southeastern convergence of paragraph P4 eastern US upper ridge and north-central Atlantic upper anticyclone mentioned in paragraph P7. This surface ridge continues to have a center that has recently moved into western Europe...supported by eastern convergence of upper ridge mentioned at the end of paragraph P3.

...TROPICAL BELT DISCUSSION...
P7...Low-latitude upper ridge axis previously over the Cape Verde Islands extending into W Africa has recently lifted northward and has expanded westward into the eastern Caribbean in the wake of the weakening and or retrograding upper vorticity features mentioned in paragraph P5. Upper outflow of Caribbean portion of low-latitude upper ridging supports t-storms over much of Central America. Upper vortex east of the Lesser Antilles has retrograded westward into the eastern Caribbean while steered by paragraph P4 eastern US upper ridge...and upper vortex south of Bermuda persists...with both of these upper vortices continuing to seperate the aforementioned low-latitude upper ridge axis from the Caribbean portion of low-latitude upper ridging. South end of all the low-latitude upper ridging in this paragraph...in conjunction with the south end of the paragraph P6 surface ridge...is also advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Lastly...a portion of the low-latitude upper ridging has evolved into new north-central Atlantic upper anticyclone supported by warm air advection ahead of 1004 mb depression mentioned in paragraph P2. Relatively lower pressures south of the new upper anticyclone and north of the low-latitude upper ridging supports new embedded upper vortex in the open central Atlantic.

P8...All the surface troughing mentioned in paragraph P7 of the previous discussion has consolidated into central Gulf of Mexico surface trough supported by eastern divergence of paragraph P5 north-central Gulf upper vortex...as well as a northward-extending surface trough that has moved westward from the SE US and into the Arkansas...Lousiana...Oklahoma...Texas region. This northward-extending surface trough continues to be supported by split flow upper divergence between easterlies on the north side of the paragraph P5 north-central Gulf upper vortex and southerlies on the west side of the paragraph P4 eastern US upper ridge. The central Gulf surface trough had associated t-storms from the Yucatan peninsula northeastward into Florida yesterday afternoon...but no tropical development is expected as these t-storms have recently died down. The northward-extending surface trough produced its own impressive t-storm cluster over the Arkansas yesterday afternoon as well.

P9...Tropical wave previously in the central Caribbean is moving into Central America...where its surface convergence is further agitating the Central America t-storm activity mentioned in paragraph P7 above.

P10...Tropical wave previously crossing the Lesser Antilles into the eastern Caribbean is now over Haiti this morning. In the past 24 hours...its thunderstorm activity has continued to intensify thanks to split flow upper divergence at the boundary between the paragraph P7 eastern Caribbean upper vortex and paragraph P7 upper vortex south of Bermuda. As this tropical wave continues WNW across Cuba...the Bahamas...south Florida...and into the Gulf of Mexico (while steered by SW quad of paragraph P6 surface ridge)...will be watching for development potential as this tropical wave is expected to slide under a favorable upper anticyclone shown in models to develop between the paragraph P5 north-central Gulf upper vortex and paragraph P7 upper vortex south of Bermuda. However...currently their is no computer model showing development of this tropical wave.

P11...Tropical wave previously west of the Cape Verde Islands is now midway between the Cape Verdes and Lesser Antilles. While some t-storms persist in its south half...its north half remains suppressed by dry Saharan air mentioned in paragraph P7.

2013 Atlantic Hurricane Season Birdseye Discussion #45

By: NCHurricane2009, 8:06 AM GMT on July 18, 2013

...THURSDAY JULY 18 2013 4:07 AM EDT...
Atlantic tropics continue to remain quiet...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_17_2013_2345Z_zpsd9faa4be.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_17_2013_2345Z_zps5186b6bc.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper trough and associated surface frontal cyclone continues east across Hudson Bay into eastern Canada. Western convergence of the upper trough supports 1023 mb surface ridge over southern Manitoba.

P2...Upper trough previously over the Atlantic high seas between Canada and Greenland is now SSE of Greenland...with eastern divergence of the upper trough supporting a 994 mb surface frontal cyclone currently SSE of the south tip of Greenland. Western convergence of this upper trough supports 1022 mb surface ridge currently just south of Newfoundland. Warm air advection ahead of 994 mb frontal cyclone supports building upper ridge west of Europe

P3...Cut-off upper vortex previously over Texas has shifted westward into southern New Mexico while retrograding about eastern US upper ridge mentioned further down in this paragraph. Decaying north-central Atlantic front...NW Atlantic surface low south of Nova Scotia...and surface trough just offshore of the US mid-Atlantic states...all mentioned in paragraph P3 of the previous discussion...currently persists as surface troughing from the mid-Atlantic states eastward into the open central Atlantic for several hundred miles all still supported by split flow upper divergence between easterlies southeast of the eastern US upper ridge mentioned further down this paragraph and mainstream mid-latitude westerlies. What is now the 1021 mb surface ridge centered just offshore of the NE US supports eastern US upper ridge with low-level warm air advection on its west side...and in turn SE convergence of the upper ridge supports the surface ridge.

P4...Cut-off upper trough previously west of the Azores is currently the upper vortex just north of the Azores while the associated surface frontal depression has dissipated below it. A southwest portion of this upper vorticity several days ago has evolved into what is now the upper vortex moving into the eastern Gulf of Mexico that continues retrograding westward about the eastern US upper ridge mentioned in paragraph P3.

P5...Surface ridge dominates much of the open Atlantic basin. This surface ridge continues to have a center west of Europe...currently 1030 mb and currently supported by eastern convergence of upper ridge mentioned at the end of paragraph P2.

...TROPICAL BELT DISCUSSION...
P6...Low-latitude upper ridge axis previously over the Cape Verde Islands extending into W Africa has recently lifted northward and has expanded westward into the eastern Caribbean in the wake of the weakening and or retrograding upper vorticity features mentioned in paragraph P4. Upper outflow of Caribbean portion of low-latitude upper ridging supports t-storms that have shifted from Panama and into much of Central America. New upper vortices...one south of Bermuda...one in the Central Caribbean...and one east of the Lesser Antilles...have developed in relatively lower pressures between the low-latitude upper ridging mentioned in this paragraph and eastern US upper ridge mentioned in paragraph P3. South end of the aforementioned low-latitude upper ridging...in conjunction with the south end of the paragraph P5 surface ridge...is also advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Surface trough entering the eastern Gulf of Mexico has undergone a northward expansion into the SE US where a large batch of t-storms developed this past afternoon...this expansion supported by split flow upper divergence between easterlies on the north side of the paragraph P4 eastern Gulf upper vortex and southerlies on the west side of the paragraph P3 eastern US upper ridge. Eastern divergence of the paragraph P4 eastern Gulf upper vortex supports surface trough that has moved from north of Puerto Rico to northeast of the Bahamas in the last 24 hrs...while a divergent upper westerly jet south of the upper vortex and north of the paragraph P6 Caribbean low-latitude upper ridging supports a new surface trough over the western Yucatan. Thunderstorms span the area between the new Yucatan surface trough and surface trough northeast of the Bahamas.

P8...Tropical wave previously in the eastern Caribbean is now in the central Caribbean...and remains inactive while caught in a batch of Saharan dry air accumulated below new upper vortex in the central Caribbean mentioned in paragraph P6.

P9...Tropical wave previously nearing the Lesser Antilles is crossing the islands into the eastern Caribbean this early morning...and although previously suppressed by paragraph P6 Saharan dry now has some cloud and shower actvity supported by split flow upper divergence at the boundary between the paragraph P6 upper vortex east of the Lesser Antilles and paragraph P6 upper vortex south of Bermuda.

P10...Tropical wave previously SE of the Cape Verde Islands is now just west of the islands...with t-storms persisting in its south half while its north half is choking on dry Saharan air mentioned in paragraph P6.

2013 Atlantic Hurricane Season Birdseye Discussion #44

By: NCHurricane2009, 4:56 AM GMT on July 17, 2013

...WEDNESDAY JULY 17 2013 1:00 AM EDT...
Atlantic tropics remain quiet...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_16_2013_2045Z_zps4afbe022.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1921Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_16_2013_2045Z_zps3eaaaae6.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and associated surface frontal cyclone is entering the upper-left corner of the above charts from western Canada and Hudson Bay.

P2...Upper trough previously emerging onto the east Canada coast has entered the Atlantic high seas between Canada and Greenland...with eastern divergence of the upper trough supporting an intensifying 988 mb surface frontal cyclone currently south of Greenland. Western convergence of this upper trough supports 1026 mb surface ridge currently over eastern Canada.

P3...Pair of cut-off upper vortices persists in northern Texas and western Gulf of Mexico. Decaying Texas front is now a surface trough supported by eastern divergence of the north Texas upper vortex. Decyaing north-central Atlantic front with 1014 mb depression...NW Atlantic surface low south of Nova Scotia...and now a new surface trough just offshore of the US mid-Atlantic states...all mentioned in paragraph P2 of the previous discussion...persists while now supported by split flow upper divergence between easterlies southeast of the eastern US upper ridge mentioned further down this paragraph and mainstream mid-latitude westerlies. What is now the 1027 mb NE US surface ridge supported eastern US upper ridge with low-level warm air advection on its west side...and in turn SE convergence of the upper ridge supported the surface ridge. Now that the surface and upper ridge centers have become vertically stacked...we have a deep-layered ridge centered over southern Michigan this early morning.

P4...Cut-off upper trough west of the Azores...mentioned in paragraph P3 of the previous discussion...persists. Surface frontal depression west of the Azores also mentioned in paragraph P3 of the previous discussion has weakened into a surface trough while remaining vertically stacked with the upper trough. In the last nine days...a fragment of this upper vorticity had also split southeastward and is currently the upper trough due north of the Canary Islands heading into western Europe (moreover a southwest portion of this upper vorticity had also evolved into what is now the upper vortex due southwest of Bermuda that is retrograding westward about the eastern US upper ridge mentioned in paragraph P3).

P5...Surface ridge dominates much of the open Atlantic basin. The west end of this surface ridge is getting a westward extension tonight while the southern Michigan 1027 mb center in paragraph P3 merges with it. Remainder of the open Atlantic portion of this surface ridge continues to have a 1026 mb center west of Europe.

...TROPICAL BELT DISCUSSION...
P6...Low-latitude upper ridge axis previously over the Cape Verde Islands extending into W Africa continues lifting northward and has expanded westward toward the Lesser Antilles/E Caribbean in the wake of the weakening and or retrograding upper vorticity features mentioned in paragraph P4. Upper trough vorticity has recently diminished in the central Caribbean such that the low-latitude upper ridge axis is beginning to join the Caribbean portion of low-latitude upper ridging which has recently developed a south-central Caribbean upper anticyclone and associated t-storms near and over Panama. Northern Yucatan and central Gulf of Mexico t-storms mentioned in paragraph P5 of the previous discussion have recently left the domain of the Caribbean low-latitude upper ridging...transfering into the western Gulf of Mexico while becoming associated with a new surface trough supported by split flow upper divergence at the boundary between the two upper vortices mentioned in paragraph P3. South end of the aforementioned low-latitude upper ridge axis...in conjunction with the south end of the paragraph P5 surface ridge...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Surface trough previously just east of Florida (and associated upheaveal in t-storms that has occurred with it in the last 24 hrs) is now entering the eastern Gulf of Mexico while currently supported by split flow upper divergence at the boundary between the west side of the paragraph P4 upper vortex SW of Bermuda and paragraph P3 upper vortex in the western Gulf of Mexico. Eastern divergence of the paragraph P4 upper vortex SW of Bermuda continues supporting relatively new surface trough and associated t-storms north of Puerto Rico.

P8...Tropical wave previously approaching the Lesser Antilles has crossed the islands into the eastern Caribbean...and remains suppressed by dry Saharan air mentioned in paragraph P6. Albeit it has recently begun entering an area of moistening eastern Caribbean air associated with enhanced poleward upper outflow at the west end of the expanding low-latitude upper ridge axis mentioned at the beginning of paragraph P6.

P9...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles is nearing the Lesser Antilles while suppressed by dry Saharan air mentioned in paragraph P6.

P10...Tropical wave with loose t-storm clustering is emerging from western Africa into the Atlantic tropical waters SE of the Cape Verde Islands tonight. No computer model support for this tropical wave's development even though it will traverse below the low shear and enhanced upper outflow enviroment of low-latitude upper ridge axis mentioned in paragraph P6. This is probably because the tropical wave will likely choke on dry Saharan air like its predecessor tropical waves mentioned in paragraphs P8 and P9.

2013 Atlantic Hurricane Season Birdseye Discussion #43

By: NCHurricane2009, 2:00 AM GMT on July 16, 2013

...MONDAY JULY 15 2013 10:00 PM EDT...
Atlantic tropics are currently taking a mid-July snooze...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_15_2013_2045Z_zpse537a5ad.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_15_2013_2045Z_zps0890e084.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper trough previously over the north-central US and eastern Canada is about to emerge onto the east Canada coast...with eastern divergence of the upper trough supporting a 1001 mb frontal depression along the coast. Western convergence of this upper trough supports 1028 mb surface ridge currently over southern Hudson Bay.

P2...Upper trough previously moving by southern Greenland is now southeast of Greenland...while the cut-off upper trough over the Gulf of Mexico and eastern US have split into a pair of cut-off upper vortices (one over northern Texas and the other over the western Gulf) retrograding westward about the eastern US upper ridge mentioned further down in this paragraph. Eastern divergence of these upper vorticity features previously supported a lengthy front which has now decomposed into a southern Texas decaying front supported by split flow upper divergence at the boundary between the two upper vortices...another NW Atlantic front moving into the north-central Atlantic with 1014 mb depression supported by eastern divergence of the upper trough SE of Greenland...and finally another front SE of Greenland also supported by eastern divergence of the upper trough SE of Greenland. Meanwhile westerly flow across the upper trough SE of Greenland splits with northerly flow east of the eastern US upper ridge mentioned further down in this paragraph...this split flow upper divergence resulting in new less-than-1020 mb surface low due south of Nova Scotia in the NW Atlantic. Western convergence of the upper trough SE of Greenland previously supported what is now the 1028 mb NE US surface ridge...but low-level warm air advection on the west side of this ridge has over the last 48 hrs pumped up the upper ridge over the eastern US whose SE convergence now supports this 1028 mb ridge.

P3...Cut-off upper vortices west and north of the Azores...mentioned in paragraph P4 of the previous discussion...are now upper troughs. Surface frontal depression west of the Azores also mentioned in paragraph P4 of the previous discussion has weakened while remaining deep-layered with one of the above-mentioned upper vortices/troughs. In the last eight days...a fragment of this upper vorticity had also split southeastward and is currently the upper trough due north of the Canary Islands (moreover a southwest portion of this upper vorticity had also evolved into what is now the upper vortex due southwest of Bermuda that is retrograding westward about the eastern US upper ridge mentioned in paragraph P2).

P4...Surface ridge dominates much of the open Atlantic basin. The west end of this surface ridge is getting a westward extension tonight while the NE US 1028 mb ridge mentioned in paragraph P2 merges with it. Remainder of the open Atlantic portion of this surface ridge continues to have an eastern greater-than-1024 mb center west of Europe.

...TROPICAL BELT DISCUSSION...
P5...Low-latitude upper ridge axis previously over the Cape Verde Islands extending into W Africa is lifting northward and has expanded westward toward the Lesser Antilles in the wake of the weakening and or retrograding upper vorticity features mentioned in paragraph P3. Upper trough vorticity persists in the central Caribbean such that the low-latitude upper ridge axis remains split from the Caribbean portion. The Caribbean portion of the low-latitude upper ridging extends from Central America northeastward into the W Caribbean waters. Western Caribbean t-storms mentioned in paragraph P8 of the previous discussion have shifted westward into the northern Yucatan and central Gulf of Mexico while becoming associated with the vertical lift instigated by the split southerly upper flow located at the boundary between the paragraph P2 western Gulf upper vortex and the Caribbean portion of the upper ridging mentioned in this paragraph. South end of the aforementioned low-latitude upper ridge axis...in conjunction with the south end of the paragraph P4 surface ridge...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P6...Surface trough previously northeast of the Bahamas is now just east of Florida while currently supported by split flow upper divergence between northerlies west of the paragraph P3 upper vortex SW of Bermuda and easterlies south of the paragraph P2 eastern US upper ridge. Eastern divergence of the upper vortex supports new surface trough north of Puerto Rico.

P7...Tropical wave previously midway between the Lesser Antilles and Cape Verde Islands is now approaching the Lesser Antilles and remains suppressed by dry Saharan air mentioned in paragraph P5.

P8...Tropical wave previously southwest of the Cape Verde Islands is now midway between the Cape Verde Islands and Lesser Antilles while also suppressed by dry Saharan air mentioned in paragraph P5.

2013 Atlantic Hurricane Season Birdseye Discussion #42

By: NCHurricane2009, 11:11 PM GMT on July 14, 2013

...SUNDAY JULY 14 2013 7:09 PM EDT...
Remnants of Chantal diminish and is no longer a special feature on this blog. See paragraph P7 for update statement on the remnants. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_14_2013_1815Z_zps907a3d66.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1927Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_14_2013_1815Z_zps19f0a779.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and surface frontal system has entered the upper-left corner of the above atmo charts from western Canada...with the surface fronts now having arrived into the north-central US and eastern Canada. Western convergence of this upper trough supports 1027 mb surface ridge just NE of Montana.

P2...Upper trough moving by southern Greenland remains in the same general location in the last 24 hrs...cut-off upper trough over the Gulf of Mexico and eastern US from the previous discussion is retrograding westward about the eastern US upper ridge mentioned further down in this paragraph. Eastern divergence of both upper trough fragments previously supported a lengthy front which has now decomposed into a northern Gulf to Texas decaying front (featuring a 1014 mb low pressure in the NE Gulf highlighted in NHC's tropical weather outlook yesterday and now cancelled as it makes landfall in the Florida panhandle)...another NW Atlantic front with 1018 mb depression supported by eastern divergence of the northern upper trough fragment...and finally another front SE of Greenland. Western convergence of the northern upper trough fragment previously supported what is now the 1027 mb ridge that has moved southeastward from the Great Lakes into the NE US...but low-level warm air advection on the west side of this ridge has rapidly pumped up a new upper ridge over the eastern US whose SE convergence now supports this 1027 mb ridge. Upper anticyclone to the SE of Greenland persists ahead of both upper trough fragments...while the upper anticyclone offshore of the NE US has been absorbed by aforementioned eastern US upper ridge.

P3...Central US upper anticyclonic ridge has been pushed southwestward into the SW US due to cool air advection behind front mentioned in paragraph P1.

P4...Upper trough previously in the NE Atlantic high seas has moved into western Europe...but its southwest end leaves behind cut-off upper vortices west and north of the Azores. What is left of the lengthy open Atlantic front supported by this upper trough is a 1017 mb frontal depression west of the Azores that has become deep-layered while becoming stacked with one of the above-mentioned upper vortices. In the last seven days...a fragment of this upper trough had also split southeastward and is currently the upper trough midway between the Azores and Canary Islands (moreover a southwest portion of this upper trough fragment has evolved into what is now the upper vortex due south of Bermuda that is beginning to retrograde westward about the eastern US upper ridge mentioned in paragraph P2).

P6...Surface ridge dominates much of the open Atlantic basin. The west end of this surface ridge is getting a westward extension tonight while the NE US 1027 mb ridge mentioned in paragraph P2 merges with it. Remainder of the open Atlantic portion of this surface ridge has an eastern 1028 mb center west of Europe supported by southeastern convergence of upper anticyclone SE of Greenland mentioned in paragraph P2.

...TROPICAL BELT DISCUSSION...
P7...South end of the remnant tropical wave of Chantal has crossed southeastern Mexico and is exiting the picture while moving into the eastern Pacific. Whatever weather is left of the north end of the tropical wave is a t-storm cluster east of Florida associated with split flow upper divergence between northerlies on west flank of paragraph P4 upper vortex south of Bermuda and southeasterlies on the SW quad of paragraph P2 eastern US upper ridge.

P8...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the the Caribbean. This upper ridging continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa. Upper trough vorticity persists in the central Caribbean such that the above-mentioned low-latitude axis is split from the Caribbean portion. The Caribbean portion of the low-latitude upper ridging extends from Central America northeastward into the W Caribbean waters...with the upper outflow of this portion supporting W Caribbean t-storms (perhaps these t-storms were earlier enhanced by surface convergence associated with the south end of Chantal's remnant wave mentioned in paragraph P7 when that wave fragment earlier went by this area). What's left of what was an embedded SW-NE oriented string of upper vorticity in this upper ridging is now an escaping upper vortex northern Spain. Days ago the south end of all the upper ridging mentioned in this paragraph (in conjunction with the south end of the paragraph P6 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air is mitigated as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart.

P9...Surface trough previously north of Puerto Rico is now north of Hispaniola and northeast of the Bahamas...and remains largely inactive while suppressed below paragraph P4 upper vortex located south of Bermuda with the exception of the north end of the surface trough that has t-storms due to split flow upper divergence between northerlies west of the upper vortex and easterlies south of the paragraph P2 eastern US upper ridge.

P10...Tropical wave southwest of the Cape Verde Islands is now midway between the Lesser Antilles and Cape Verde Islands remains suppressed by dry Saharan air mentioned in paragraph P8 despite being below a favorable environment of low shear and enhanced outflow of low-latitude upper ridge axis also mentioned in that paragraph.

P11...Vigorous tropical wave previously exiting the African coast is already southwest of the Cape Verde Islands and has become less organized while its northwest half ingests dry Saharan air mentioned in paragraph P8.

2013 Atlantic Hurricane Season Birdseye Discussion #41

By: NCHurricane2009, 2:15 PM GMT on July 13, 2013

...SATURDAY JULY 13 2013 10:20 AM EDT...
Still watching the remnants of Chantal currently tracking northwest toward the Carolinas. Visible satellite imagery this morning suggests the system is developing a low-level circulation just to the north of its thunderstorm cluster. Regardless of development...expect heavier weather to move into the Carolinas in the next 24 hours. See Chantal special feature section below for additional details.

Due to apparent choking on dry air...I have cancelled the tropical wave southwest of the Cape Verde Islands as a special feature on this blog. See paragraph P10 for update statement on this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_13_2013_0915Z_zps74f32092.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0726Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_13_2013_0915Z_zps8164ef6f.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...REMNANTS OF CHANTAL (INVEST 96-L)...
South end of the remnant tropical wave of Chantal is heading across the western Caribbean and Central America...and will soon be crossing southeastern Mexico. It is the north end of the remnant tropical wave that is more interesting while maintaining a cluster of thunderstorms currently north of the western Bahamas in the outflow of an upper ridge that exists due to relatively higher upper-level pressures between paragraph P2 southern upper trough fragment and paragraph P4 upper vortex SE of Bermuda. The Naval Research Laboratory site of the US Navy considers this system as Invest 96-L...but a statement on the site also indicates that Chantal and 96-L are the same system.

Visible satellite imagery suggests a low-level circulation is developing on the north side of the thunderstorm cluster. The system is tracking northwestward toward the Carolinas while steered by paragraph P2 1025 mb Great Lakes surface ridge. Once this system makes landfall in the next 24 hours...I will drop it as a special feature on this blog. Regardless of whether or not this system spins up into a tropical cyclone before landfall...expect heavier weather to move into the Carolinas.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and surface frontal system continues entering the upper-left corner of the above atmo charts from western Canada.

P2...Upper trough previously over the northern US and eastern Canada has split into one upper trough moving by southern Greenland and a second cut-off upper trough over the Gulf of Mexico and eastern US. Eastern divergence of both upper trough fragments supports a lengthy front extending from the SE US...north-northeastward to the waters east of Greenland (with a 1016 mb frontal depression developing over Maryland). Western convergence of the northern upper trough fragment supports 1025 mb ridge over the Great Lakes...SE Canada...and eastern US. Upper ridge offshore of eastern North America ahead of both upper trough fragments has also split into two...with one upper anticyclone to the SE of Greenland and another anticyclone offshore of the NE US. The National Hurricane Center (NHC) just highlighted a small area in the northeastern Gulf of Mexico where a surface low could form from the eastern divergence of the southern upper trough fragment. Such a surface low would be close to shore and move northwestward into land quickly while steered by the above-mentioned 1025 mb ridge such that I believe any subtropical or tropical cyclone development from this system is unlikely.

P3...Western US upper anticyclonic ridge has shifted eastward into the central US.

P4...Upper trough previously in the NE Atlantic high seas is moving into western Europe...but its southwest end leaves behind a new cut-off upper vortex just west of the Azores. Eastern divergence of this upper trough supports lengthy front from the open central Atlantic extending NNE into the British Isles (a 1018 mb depression is located west of the Azores...just to the southeast of the new upper vortex...and along this front). In the last six days...a fragment of this upper trough has split southeastward and is currently the upper vortex over the eastern Azores (and a southwest portion of this upper trough fragment has evolved into what is now the upper vortex SE of Bermuda).

P5...Upper vortex over the Florida Straits has become absorbed by southern upper trough fragment mentioned in paragraph P2.

P6...Surface ridge dominates much of the open Atlantic basin. Its northern Gulf of Mexico extension currently with a 1015 mb center was formerly supported by southeast convergence of paragraph P3 central US upper ridge...but this Gulf portion is now dissipating due to incoming paragraph P2 weather system. Remainder of the open Atlantic portion of this surface ridge has split into two due to the front mentioned in paragraph P4. One portion is a 1025 mb center NE of Bermuda supported by eastern convergence of paragraph P2 NE US upper anticyclone. The other portion extends from the vicinity of the Cape Verde Islands northward into western Europe.

...TROPICAL BELT DISCUSSION...
P7...Upper troughing persists previously in the Gulf of Mexico has been absorbed byt southern upper trough fragment mentioned in paragraph P2.

P8...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the the Caribbean. This upper ridging also continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa. Upper trough vorticity persists in the south-central Caribbean (and also midway between the Cape Verdes and Lesser Antilles as mentioned in paragraph P9 of the previous discussion) such that the above-mentioned low-latitude axis is split from the Caribbean portion. The Caribbean portion of the low-latitude upper ridging extends from Central America northeastward towards the remnants of Chantal. What's left of what was an embedded SW-NE oriented string of upper vorticity in this upper ridging is now an escaping upper vortex over NW Spain. Days ago the south end of all the upper ridging mentioned in this paragraph (in conjunction with the south end of the paragraph P6 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air is mitigated as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart.

P9...Surface trough previously northeast of the Lesser Antilles is moving westward while steered by southwest corner of paragraph P6 surface ridge. The surface trough is now currently north of Puerto Rico and remains largely inactive while suppressed below paragraph P4 upper vortex SE of Bermuda with the exception of the north end of the surface trough that has t-storms due to split flow upper divergence between northerlies west of the upper vortex and easterlies south of the paragraph P2 upper anticyclone offshore of the NE US.

P10...Tropical wave southwest of the Cape Verde Islands...previously a special feature on this blog...has lost t-storm activity due to ingestion of dry Saharan air mentioned in paragraph P8. It is below a favorable environment of low shear and enhanced outflow of low-latitude upper ridge axis also mentioned in paragraph P8...but until this environment assists the tropical wave against the dry air...tropical cyclone development is not expected from this tropical wave.

P11...Vigorous tropical wave with curved t-storm bands west of its axis is entering the favorable low shear and enhanced outflow environment below paragraph P8 low-latitude upper ridge axis as it exits the African coast into the Atlantic tropics. Even though this tropical wave is showing early signs of impressiveness...it may not develop due to possible later ingestion of dry air as we have recently seen with the tropical wave in paragraph P10.

2013 Atlantic Hurricane Season Birdseye Discussion #40

By: NCHurricane2009, 3:56 PM GMT on July 12, 2013

...FRIDAY JULY 12 2013 11:55 AM EDT...
This discussion has taken longer to release than previously anticipated. This is because of my current vacationing with limited computer access...

As special update #39A stated...still watching the remnants of Chantal currently over the Bahamas. See Chantal special feature section for additional details.

Although the tropical wave southwest of the Cape Verde Islands has lost t-storm activity...still maintaining it as a special feature section on this blog for now due to forecast favorable upper winds over the next few days. See second special feature section below for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_12_2013_1215Z_zps0ba1c4d1.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1326Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_12_2013_1315Z_zpsd0be6297.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...REMNANTS OF CHANTAL (INVEST 96-L)...
South end of the remnant tropical wave of Chantal is heading across the Caribbean and into Central America. It is the north end of the remnant tropical wave that is more interesting while developing a cluster of thunderstorms over the Bahamas in the outflow of an upper ridge that exists due to relatively higher upper-level pressures between paragraph P5 Florida Straits upper vortex and paragraph P4 upper vortex SE of Bermuda. The Naval Research Laboratory site of the US Navy considered this system as Invest 96-L...but a statement on the site also indicates that Chantal and 96-L are the same system.

Technically the north end of the remnat tropical wave is now moving below the less favorable enivronment beneath the Florida straits upper vortex...perhaps which is why the NHC (National Hurricane Center) recently downgraded the potential for this system to regenerate into a tropical cyclone. However I am still keeping this a special feature on this blog in case the system redevelops a new surface trough direclty below the outflow of the nearby upper ridge and below the thunderstorms over the Bahamas. If this system indeed regenerates over the Bahamas...it will track northwest about the west side of low-level Atlantic subtropical ridge mentioned in paragraph P6...then curve westward into the southeastern United States due to the Great Lakes-to-SE Canada surface ridge mentioned in paragraph P2. The only computer model that suggests the redevelopment of Chantal is the CMC...but admittedly the CMC tends to overdo tropical cyclones. Interests in the Bahamas....and anywhere from Florida and into the Carolinas should continue to monitor this situation carefully over the next couple of days...

...SPECIAL FEATURE...TROPICAL WAVE SOUTHWEST OF THE CAPE VERDE ISLANDS...
Tropical wave southwest of the Cape Verde Islands has lost t-storm activity even though it is below a favorable environment of low shear...enhanced outflow...and moisture re-surgence toward Africa (all associated with low-latitude upper ridge axis mentioned in paragraph P8). However their is still decent cyclonic turning in the remaining cloudiness. Perhaps this tropical wave coughed on some of the Saharan dry air to the northwest. However the position of the tropical wave in NHC TAFB maps...coupled with the above thermo chart...suggests this tropical wave is still largely embedded in the moisture resurgence toward Africa (both the dry air and moisture re-surgence regions are discussed in paragraph P8). As the paragraph P4 upper vortex currently east of Bermuda retrogrades westward...models show the favorable low-latitude upper ridge axis expanding westward in its wake. Therefore favorable upper winds are likely to last as the tropical wave continues westward while steered by the south side of the paragraph P6 surface ridge. Therefore I am still gambling that this system has a high probability of eventually becoming a tropical cyclone and continue to hold it as a special feature on this blog.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and surface frontal system is entering the upper-left corner of the above atmo charts from western Canada.

P2...Upper trough previously over the northern US and eastern Canada is undergoing a long anticipated northern and southern split. Eastern divergence of the upper trough supports 984 mb surface frontal cyclone currently centered between Canada and Greenland...and western convergence of the upper trough supports 1024 mb ridge over the Great Lakes and SE Canada. Warm air advection ahead of the 984 mb cyclone and its lengthy front supports upper ridge just offshore of the east North American coast.

P3...Western US upper ridge persists.

P4...Upper trough previously in the Atlantic high seas over and south of Greenland is now in the NE Atlantic high seas. Eastern divergence of this upper trough supports lengthy front from the open central Atlantic extending NNE into the waters offshore of the British Isles (a new 1016 mb depression is located west of the Azores and along this front). Western convergence of this upper trough system supports 1026 mb surface ridge currently due south of Greenland. In the last 120 hrs a fragment of this upper trough has split southeastward and is currently located over the Azores (and a southwest portion of this upper trough fragment has evolved into what is now the upper vortex SE of Bermuda).

P5...Upper vortex persists over the Florida Straits.

P6...Surface ridge dominates much of the open Atlantic basin. Its northern Gulf of Mexico extension currently with a 1015 mb center was formerly supported by southeast convergence of paragraph P3 western US upper ridge...but this Gulf portion is now dissipating due to incoming paragraph P2 weather system. Remainder of the open Atlantic portion of this surface ridge has split into two due to the front mentioned in paragraph P4. One portion is a 1023 mb center NE of Bermuda supported by eastern convergence of upper ridge just offshore of North America mentioned in paragraph P2. The other portion extends from the vicinity of the Cape Verde Islands northward into western Europe.

...TROPICAL BELT DISCUSSION...
P7...Upper troughing persists over parts of the Gulf of Mexico in relatively lower pressures south of the western US upper ridge in paragraph P3.

P8...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the the Caribbean. This upper ridging also continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa. Inverted upper trough vorticity persists in the south-central Caribbean such that the Caribbean upper anticyclonicity remains split into an eastern Caribbean upper ridge axis and another upper ridge axis extending from Central America northeast toward the remnants of Chantal. What's left of what was an embedded SW-NE oriented string of upper vorticity in this upper ridge is now an escaping upper trough northeast of the Canary Islands. Days ago the south end of all the upper ridging mentioned in this paragraph (in conjunction with the south end of the paragraph P6 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air is mitigated as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart.

P9...As mentioned in paragraph P8...east Caribbean upper ridge axis persists. Tropical wave previously midway between the Cape Verdes and Lesser Antilles is fully suppressed by dry Saharan air also midway between the Cape Verdes and Lesser Antilles re-enforced by convergent east side of the east Caribbean upper ridge axis. The tropical wave is also suppressed by low-latitude upper trough that exists due to relatively lower pressures east of this upper ridge axis. In the last 24 hrs...this tropical wave has merged with a surface trough northeast of the Lesser Antilles. This surface trough appears supported by eastern divergence of paragraph P4 upper vortex SE of Bermuda...and perhaps this surface trough originated as a southwest fracture of lengthy surface front also mentioned in paragraph P4.

2013 Atlantic Hurricane Season Birdseye Discussion #39A (Special Update)

By: NCHurricane2009, 10:19 PM GMT on July 11, 2013

...THURSDAY JULY 11 2013 6:17 PM EDT...
The north end of the remnant tropical wave of Chantal is becoming better organized over the Bahamas beneath a developing favorable upper ridge in relatively higher pressures between Florida Straits upper vortex and upper vortex coming in from the east from Bermuda. Therefore I will be re-upgrading it to a special feature in my next full blog post tonight/early tomorrow morning.

From this location....the remnant will track northwest about the west side of low-level Atlantic subtropical ridge...then curve westward into the southeastern United States due to another ridge building to the north associated with the western convergent side of United States upper trough. Therefore interests in the Bahamas....and anywhere from Florida and into the Carolinas should monitor this situation carefully over the next couple of days...

2013 Atlantic Hurricane Season Birdseye Discussion #39

By: NCHurricane2009, 8:37 AM GMT on July 11, 2013

...THURSDAY JULY 11 2013 4:37 AM EDT...
Chantal degenerates into a tropical wave currently affecting Haiti...the Dominican Repbulic...and the eastern Bahamas with thunderstorm activity. See paragraph P9 for update statement on the remnants of Chantal.

The eastern of the two tropical waves behind Chantal has become better organized southwest of the Cape Verde Islands. Due to the forecast favorable upper winds for the next few days...I have upgraded this tropical wave to a special feature on this blog. See special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_10_2013_2345Z_zps67025f01.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_10_2013_2345Z_zps86a11351.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE SOUTHWEST OF THE CAPE VERDE ISLANDS...
Tropical wave previously southeast of the Cape Verde Islands is now southwest of the islands. While taking advantage of low shear...enhanced outflow...and moisture re-surgence toward Africa (all associated with low-latitude upper ridge axis mentioned in paragraph P7)...thunderstorms in the western vicinity of the tropical wave appear to be organizing into a low pressure area with some spiral banding. As the paragraph P3 upper vortex currenlty east of Bermuda retrogrades westward...models show the favorable low-latitude upper ridge axis expanding westward in its wake. Therefore these favorable conditions are likely to last as the tropical wave continues westward while steered by the south side of the paragraph P5 surface ridge. With the early signs of organization beginning and the favorable conditions that lie ahead...I am gambling that this system has a high probability of eventually becoming a tropical cyclone and have upgraded it to a special feature this early morning.

...MID-LATITUDES DISCUSSION...
P1...Upper trough from western Canada has entered the northern US and eastern Canada. Eastern divergence of the upper trough supports 993 mb surface frontal cyclone centered over NE Hudson Bay...and western convergence of the upper trough supports 1017 mb ridge over the north-central US. Warm air advection ahead of the 993 mb cyclone supports upper ridge over the NE US and eastern tip of Canada.

P2...Western US upper ridge...mentioned in paragraph P2 of the previous discussion...persists.

P3...Upper trough...with attendant surface frontal cyclone featuring a 1005 mb center over southern Greenland...is located in the Atlnatic high seas over and south of Greenland. Western convergence of this upper trough system supports 1024 mb surface ridge between Newfoundland and Greenland. In the last 96 hrs a fragment of this upper trough has split southeastward and is currently located over the Azores (and a southwest portion of this upper trough fragment has evolved into relatively new upper vortex east of Bermuda). Low-level warm air advection ahead of the 1005 mb center is supporting an amplifying upper ridge east of Greenland just outside of the above charts.

P4...Upper vortex has moved southwest from the W Bahamas and into the Florida straits while steered by paragraph P2 western US upper ridge.

P5...Surface ridge dominates much of the open Atlantic basin. Its northern Gulf of Mexico extension currently with a 1018 mb center is supported by southeast convergence of western US upper ridge...but this Gulf portion is expected to erode due to eastern divergence of paragraph P1 upper trough. A 1022 mb center over Bermuda is supported by eastern convergence of NE US upper ridge mentioned in paragraph P1. This surface ridge continues to have a northeastern lobe extending into western Europe supported by eastern convergence of upper ridge east of Greenland mentioned at the end of paragraph P3.

...TROPICAL BELT DISCUSSION...
P6...Upper troughing persists over parts of the Gulf of Mexico in relatively lower pressures south of the western US upper ridge in paragraph P2.

P7...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the the Caribbean. This upper ridging still has upper anticyclonicity SE of the Azores...and also a new upper anticyclone SW of the Azores located between upper vortex E of Bermuda and upper trough fragment over the Azores both mentioned in paragraph P3. This upper ridging also continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa...with the west end of this upper ridge axis splitting off over the eastern Caribbean while becoming associated with the latent heat release of Chantal's t-storms (eastern convergence of this eastern Caribbean upper ridge axis is supporting sinking motion that re-enforces Saharan dry air midway between the Cape Verde Islands and Lesser Antilles). Inverted upper trough vorticity persists in the south-central Caribbean such that the Caribbean upper anticyclonicity is split into the aformentioned eastern Caribbean upper ridge axis and upper anticyclone over Costa Rica. Embedded SW-NE oriented string of upper vorticity persists over the Canary Islands...and into the waters NW of the Cape Verde Islands. Days ago the south end of all the upper ridging mentioned in this paragraph (in conjunction with the south end of the paragraph P5 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air has ended as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart (see paragraph P7 of discussion #32 for development of low-latitude upper ridging over the Cape Verde Islands).

P8...Tropical wave previously over the Yucatan has exited the picture while sliding over southeastern Mexico and the eastern Pacific.

P9...Remnant tropical wave of Chantal was looking to be headed into Jamaica overnight and into this early morning...but instead has slowed significantly over Haiti perhaps while becoming associated with the outflow of the paragraph P7 eastern Caribbean upper ridge axis pumped up by the latent heat release of the associated t-storm mass. As the Gulf of Mexico portion of the paragraph P5 ridge erodes...expect the tropical wave to round the west side of the remainder of the ridge...which should take it across Cuba...the Bahamas...Florida...and into the southeastern US region within the next 72 hours. Unfavorable factors going against Chantal's regenesis include land interaction...paragraph P4 upper vortex...paragraph P3 upper vortex east of Bermuda expected to retrograde westward toward Chantal's area...as well as the paragraph P1 and P6 upper troughs. The only favorable factors for Chantal's regenesis include any exposure to warm waters in the region...the aformentioed eastern Caribbean upper ridge axis...and any new upper ridging that could develop in between all aforementioned upper voritces. Will not be re-upgrading Chantal to a special feature on this blog until it is clear the favorable factors are winning against the numerous unfavorable factors.

P10...As mentioned in paragraph P7...west end of low-latitude upper ridge axis has broke off into east Caribbean upper ridge axis associated with Chantal's t-storm latent heat release. Tropical wave previously souhtwest of the Cape Verde Islands is now midway between the Cape Verdes and Lesser Antilles...and has become inactive while suppressed by dry Saharan air also midway between the Cape Verdes and Lesser Antilles re-enforced by convergent east side of the east Caribbean upper ridge axis. The tropical wave is also suppressed inverted upper trough that exists due to relatively lower pressures southeast of this upper ridge axis.

2013 Atlantic Hurricane Season Birdseye Discussion #38A (Special Update)

By: NCHurricane2009, 6:39 PM GMT on July 10, 2013

...WEDNESDAY JULY 10 2013 2:38 PM EDT...
Chantal refuses to open into a tropical wave...and has maintained a more westerly course and is likely to strike Jamaica instead of Haiti tonight as a result. My updated forecast versus the NHC's 11 AM EDT forecast is shown in Figure 2 below...and visit www.nhc.noaa.gov for latest NHC forecasts. Tropical storm watches and warnings are in effect for the Dominican Repbulic...Haiti...some of the Bahamian islands...and now Jamaica. The latest status of these advisories can also be found at www.nhc.noaa.gov.

Previous forecasts had indicated Chantal would make an initial northward bend in track toward Haiti while feeling the low to mid-levels of a western Bahamas upper vortex. The surface trough of the upper vortex has recenty been cancelled in NHC TAFB maps...and as Figure 1 shows the GFS (and perhaps other models) have actually been predicting the low to mid-levels of the upper vortex to weaken all along...so in hindsight I should have predicted a more westerly track toward Jamaica as we are currenlty seeing. My updated forecast track in Figure 2 is on the basis of Chantal continuing to be a shallow/weak feature steered around the low-level Atlantic ridge. I extrapolated the current and fast forward motion of Chantal for another 12 hours on the basis of the storm still being influenced by the firm western Atlantic portion of the ridge. Meanwhile the Gulf portion of the ridge (currently supported by SE convergence of western US upper ridge) is shown in models to continuously erode thru the forecast period thanks to eastern divergence of south fracture of US upper trough. So after Chantal passes by Jamaica...I predict a slowing track that curves northward toward the western Cayman Islands while the storm reaches the weakening Gulf portion of the ridge.

Intensity-wise...after weakening to 45 mph winds as I previosuly predicted...Chantal has had an upheavel in t-storms since last night which I assess to be from southeastern divergence of the western Bahamas upper vortex. Based on my forecast 12 hr position and 12 hr upper wind forecast of this afternoon's 12Z GFS model run...Chantal will still be below this upper divergence...and so I maintain her current strength for my 12 hour forecast. By 24 hrs...Chantal should be due south of the upper vortex...a region of hostile westerly shear and zero upper divergence that should rip off her current t-storms while simultaneously not supporting the flare up of new storms. This is when I forecast Chantal will have definetly opened into a remnant tropical wave with winds dying down further as the forecast loss in t-storms should reduce the mixing down of flight-level winds.

 photo Jul_10_2013_850mb_GFS_for_Chantal_zpsfff5d36d.png
Figure 1: GFS 850 mb model run from yesterday July 9 1800Z. Black arrow in each frame shows steering tendency...with a northward bend toward Haiti possible as of 18Z yesterday due to mid-levels of Bahamas vortex. With the mid-level vorticity weakening as of 12Z today...the steering tendency is now more westward to Jamaica.

 photo Jul_10_2013_TS_Chantal_Forecast2_zpsc4212fd0.png
Figure 2: Updated Forecast for Tropical Storm Chantal

Impact swath in Figure 2 is extrapolation of NHC's current tropical storm wind radius along my forecast track while slowly diminishing it thru the next 24 hrs when I think the system will have lost t-storms such that the mixing down of flight-level winds stops. Cannot rule out heavy rain with possible flash flooding over Haiti...the Dominican Republic...or Jamaica...that could occur outside the impact swath and within Chantal's current t-storm mass.

2013 Atlantic Hurricane Season Birdseye Discussion #38

By: NCHurricane2009, 6:17 AM GMT on July 10, 2013

...WEDNESDAY JULY 10 2013 2:20 AM EDT...
Speeding bullet Chantal has crossed the Lesser Antilles into the eastern Caribbean after delivering tropical storm conditions...and this early morning is showing signs of opening into a tropical wave due to her fast foward pace. See Chantal special feature section below for details. In addition...pair of vigorous tropical waves behind Chantal have become less organized and the computer model support has pulled back some...see paragraphs P9 and P10 for updates on these waves.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_9_2013_2045Z_zpsb1540ce7.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1925Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_9_2013_2045Z_zps15b00789.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM CHANTAL...
My updated forecast versus the NHC's 11 PM EDT forecast is shown in Figure 1 below...and visit www.nhc.noaa.gov for latest NHC forecasts. Tropical storm watches and warnings are in effect for the Virgin Islands...Puerto Rico...the Dominican Repbulic...Haiti...and some of the Bahamian islands. The latest status of these advisories can also be found at www.nhc.noaa.gov.

Based on the shape of the of the NHC recorded storm track in Figure 1...it appears my previous forecast accurately predicted a westward bend in track as Chantal crested the axis of inverted upper trough near the Lesser Antilles. Now this inverted upper trough has weakened as mentioned in paragraph P7...Chantal is on a more westerly course parallel to the isboars of low-level paragraph P5 ridge as a shallower/weaker tropical cyclone should be doing. Some other important observations to make are that Chantal has increased in forward speed from about 25 to 30 mph in the last 24 hrs...which appeared to have caused winds in her north half to increase to 60 to 65 mph maximum sustained within the last 24 hrs while simulatenously causing her south half to lose wind speed and even open up such that Chantal may now instead be a tropical wave. The t-storm activity in the circulation has become weaker (resulting in max winds dropping to 50 mph as of 2 AM EDT) and disheveled looking...a symptom of a system that no longer has a precise center of surface convergence where t-storms can maintain their strength and organize about. Last reconnaissance plane mission from NHC struggled to find such a precise surface center as noted in the NHC 11 PM EDT advisory. Furthermore...hot-off-the-press CMC and GFS models suggest Chantal opening into a tropical wave (although CMC later suggests a strong tropical cyclone after the wave passes Haiti...but I am skeptical as the CMC has a tendency to overdo tropical cyclones).

With these observations...my forecast in Figure 1 now suggests Chantal will dissipate into a tropical wave later this morning. I also forecast the winds coming further down to 45 mph maximum later this morning as the weakening state of the t-storms means the flight-level winds will not be as effectively mixed down to the surface. My updated track forecast is a leftward shift from my previous to account for the fact that tonight's 11 PM EDT position was a bit southwest of where I previously predicted. My updated track is also left of the current NHC as the NHC recorded storm track clearly has a leftward angle with respect to their forecast track. My updated track still agrees with a northward curve into Hispaniola (but moreso into Haiti with my leftward adjustment) as the deep-layered nature of the paragraph P4 upper vortex & surface trough pair should be able to leverage some northward pull on Chantal regradless of whether or not she is tall/strong or shallow/weak. My forecast suggests Chantal will not later re-generate into a tropical cyclone while the system gets heavily disrupted by one-two punch of land interaction with Haiti's rough terrain and southwest vertical shear ahead of paragraph P4 upper vortex.

In the small chance Chantal does not degenerate into a tropical wave later this morning...I will issue a special update with a new forecast on Chantal.

 photo Jul_10_2013_TS_Chantal_Forecast_zpsd6972424.png
Figure 1: Forecast for Tropical Storm Chantal

Impact swath in Figure 1 is initialized with the tropical storm wind radius shwown at the 11 PM EDT NHC advisory...which is biased to the right side of the storm track due to Chantal's current rapid WNW motion. I keep the swath the same size thru the forecast with the assumption Chantal remains the same size. I also keep the swath biased to the right of my forecast track thru the forecast period because of her expected fast track within my short forecast period. I dissipate the swath after 24 hours with the assumption the remnant wave of Chantal becomes so disrupted that it degenerates into an ordinary tropical wave rather than staying a vigorous one.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and attendant surface 1003 mb frontal depression centered over southern Hudson Bay is entering the upper-left corner of the above charts from western Canada and northwestern US.

P2...Cut-off upper trough that previously moved into the Azores has been absorbed by NW Atlantic upper trough fragment coming in from the west and mentioned in paragraph P3 below. Remainder of upper troughing from this system is beginning to move offshore from the NE US in between NW Atlantic upper ridge and western US upper ridge...as well as over the Texas/Mexico area as a weakening inverted upper trough to the south of the western US upper ridge.

P3...Upper trough and surface frontal system with a 1009 mb surface center is moving eastward across the high seas between Canada and Greenland (western convergence of this upper trough system supports 1023 mb surface ridge between Nova Scotia and Newfoundland...and in the last 72 hrs a fragment of this upper trough has split southeastward while moving across the NW Atlantic and now into the north-central Atlantic approaching the Azores...with its eastern divergence supporting a surface trough attached to a 1016 mb low ESE of Newfoundland as well as a southwest fragment of it becoming a small upper vortex SE of the paragraph P2 NW Atlantic upper ridge). Low-level warm air advection ahead of the 1009 mb center is supporting an amplifying upper ridge east of Greenland just outside of the above charts. Upper trough in the NE Atlantic high seas in paragraph P3 of the previous discussion as a result remains a weakened NW-SE tilted upper trough within this upper ridge and due north of the Azores. Along the lengthy front extending south and west of the 1009 mb center is a 1013 mb frontal depression that has moved from Lake Michigan and into Lake Superior in the last 24 hrs...and this depression is supported by split flow upper divergence between northerlies on the east side of the paragraph P2 western US upper ridge and mainstream mid-latitude westerlies.

P4...Upper vortex persists over the western Bahamas. Its eastern upper divergence...as well as divergence between northerlies on its west side and easterlies on the south side of the western US upper ridge...are generating showers and t-storms in the western Bahamas and Florida. This divergence during the previous discusison appeared to at least trigger mid-level pressure falls...and now it appears the pressure falls have made it to the surface with NHC TAFB declaring a surface trough moving into Florida in its recent surface maps (this surface trough may also be associated with fracture of north end of paragraph P8 tropical wave). Despite these developments...the CMC computer model has stopped showing subtropical or tropical cyclone development from this system...and other computer models continue to not support development of this system.

P5...Surface ridge dominates much of the open Atlantic basin. A western 1026 mb center over Bermuda is supported by convergence between easterlies south of the paragraph P2 NW Atlantic upper ridge and southwesterlies ahead of the paragraph P4 upper vortex. This surface ridge continues to have a northeastern lobe extending into western Europe supported by eastern convergence of upper ridge east of Greenland mentioned in paragraph P3.

...TROPICAL BELT DISCUSSION...
P6...Inverted upper trough persists over SE Mexico...as well as parts of the Gulf of Mexico...while persisting in relatively lower pressures south of the western US upper ridge mentioned in paragraph P2.

P7...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the eastern two-thirds of the Caribbean (the enhanced poleward outflow at the west lobe of the Caribbean portion supports t-storms in the south-central Caribbean and Central America area). This upper ridging still has an upper anticyclone SE of the Azores. This upper ridging also continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa...with the west end of this upper ridge axis inflated into an anticyclone due to recent latent heat release of Chantal's t-storms (eastern convergence of this upper anticyclone is supporting sinking motion that re-enforces Saharan dry air midway between the Cape Verde Islands and Lesser Antilles). Chantal's recent latent heat release has also weakened inverted upper trough near the Lesser Antilles...and pushed some of the vorticity of this inverted upper trough westward into the south-central Caribbean such that the Caribbean upper anticyclonicity has split into one anticyclone E of Nicaragua and another anticyclone north of Puerto Rico. Embedded SW-NE oriented string of upper vorticity persists over W Europe's Iberia peninsula...through the Canary Islands...and into the waters NW of the Cape Verde Islands. Days ago the south end of all the upper ridging mentioned in this paragraph (in conjunction with the south end of the paragraph P5 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air has ended as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart (see paragraph P7 of discussion #32 for development of low-latitude upper ridging over the Cape Verde Islands).

P8...Tropical wave previously over the western Caribbean has moved into the Yucatan peninsula and is becoming suppressed by paragraph P6 upper vorticity.

P9...As mentioned in paragraph P7...west end of low-latitude upper ridge axis has inflated into an upper anticyclone. Tropical wave souhtwest of the Cape Verde Islands has become less organized while suppressed by dry Saharan air midway between the Cape Verdes and Lesser Antilles re-enforced by convergent east side of the anticyclone also mentioned in paragraph P7. The tropical wave is also becoming suppressed by new inverted upper trough forming in relatively lower pressures southeast of this anticyclone.

P10...Tropical wave rolling off Africa in the previous discusison has been added to NHC TAFB maps in last 24 hrs at a location SE of the Cape Verde Islands. Its t-storm mass has become less organized and sheared southwestward from the wave axis by the easterlies on the south side of the low-latitude upper ridge axis over the Cape Verde Islands mentioned in paragraph P7...but should the latent heat release of the t-storms locally inflate the upper ridging the upper flow directly over the tropical wave could gradually become more anticyclonic and less shearing. In the event this tropical wave shows any signs of becoming better organized under less shearing...further development could become possible.

2013 Atlantic Hurricane Season Birdseye Discussion #37

By: NCHurricane2009, 7:55 AM GMT on July 09, 2013

...TUESDAY JULY 9 2013 3:55 AM EDT...
The Atlantic tropics are escalating with Tropical Storm Chantal to strike the Lesser Antilles later this morning...afterwards threatening Hispaniola (Haiti and the Dominican Republic) for a Wednesday strike. Chantal is likely to affect the Bahamas Thursday and Friday...and the southeastern United States coast by early next week. See Chantal special feature section for additional details on the tropical storm. In addition...watching a pair of vigorous tropical waves behind Chantal which are in the same favorable enviornment from which Chantal emerged and which are gaining computer model support...see paragraphs P10 and P11 for details. Should any of these waves become organized...I will be quickly upgrading them to special features on this blog.

Of note...it is unusual to have tropical cyclone activity east of the Lesser Antilles in early July. This indicates the potential for an active hurricane season ahead come August and September where a series of strong tropical waves emerging from Africa develop in the eastern open waters into potentially strong tropical cyclones.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_8_2013_2045Z_zpsd45f5309.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1917Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_8_2013_2045Z_zps7f57d1dd.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM CHANTAL...
My updated forecast versus the NHC's 11 PM EDT forecast is shown in Figure 1 below...and visit www.nhc.noaa.gov for latest NHC forecasts. Tropical storm watches and warnings have been raised for various islands in the Lesser Antilles...Virgin Islands...Puerto Rico...the Dominican Repbulic...and Haiti. The latest status of these advisories can also be found at www.nhc.noaa.gov.

My short-term outlook continues to be focused on inverted upper trough just west of Chantal located between Caribbean upper anticyclone and low-latitude upper ridge axis mentioned in paragraph P8. Rather than tracking parallel to the isobars of low-level paragraph P5 ridge (as convetional wisdom for shallow/weak tropical storm dictates)...Chantal has tracked more northward than I thought at an angle against the isobars...perhaps while also steered by east side of the inverted upper trough (even though the inverted upper trough does not go below 500 mb as shwon in GFS model initialization). It appears Chantal's strengthening and t-storms have been supported by split flow upper divergence between southerlies west of the low-latitude upper ridge axis and eaterlies flowing across the inverted upper trough...with the t-storm latent heat release expanding the west extent of the low-latitude upper ridge and pushing off the inverted upper trough to the west. I expect that the inverted upper trough will stop moving west while jamming against the Caribbean upper anticyclone...forcing Chantal to pass below the inverted upper trough later today. As such...I forecast the track to remain WNW for the first 12 hrs...then bend more westward parallel to the forecast isboars of the paragraph P5 low-level ridge between 12 and 24 hrs after Chantal crests the axis of the stalling inverted upper trough. I keep the forward speed the same thru 24 hrs with the low-level ridge maintaining current strength. Chantal shows recent signs of struggling with a lack of t-storms in her NW half as she begins passing below the inverted uper trough and whatever Sahran dry air has collected belwo the upper trough. Therefore I show no additional strengthening for first 24 hrs...then show some brisk strengthening below favorable low shear and enhanced outflow of Caribbean upper anticyclone afterwards.

As we approach 48 hrs...I agree with a gradual bend toward the north into Hispaniola (Haiti and the D.R.) initiated by east side of paragraph P4 upper vortex which has vorticity down to the mid-levels capable of grabbing Chantal even if she never becomes stronger/taller (I also show a slight slowdown by 48 hrs with the paragraph P5 ridge weakening in advance of paragraph P1 weather system). Between 48 and 96 hrs...I generally agree with the NHC curving track into the Bahamas based on the GFS model's shape of the paragraph P5 ridge's western isobars as it continues eroding in advance of the paragraph P1 weather system. I also agree with a slowing track by 96 hrs due to blocking effect of a surface ridge due north forecast to develop below western convergent side of the north split of the paragraph P1 upper trough...but my Friday night position is a bit north of the NHC's based on the GFS's position of the blocking ridge which still shows enough room in my opinion for Chantal to still advance more northward. By Saturday...the southern split of the paragraph P1 upper trough looks to have evolved into a deep-layered vortex that tries to push Chantal north against the blocking surface ridge...but I think some westerly component in the track will develop on Saturday as the blocking ridge is shown in GFS to also intensify during that time.

Intensity forecast after Chantal moves into Hispaniola (Haiti and the D.R) is uncertain. My best guess is Chantal will weaken rapidly on Wed/Thu due to the combo of mountainous terrain and westerly vertical shear southeast of the paragraph P4 upper vortex. I show no additional weakening on Friday...modeling Chantal as a storm below the east side of the upper vortex where upper southerlies are more aligned & less shearing with respect to the forecast NNW track. By Saturday...I suggest some re-strengthening as Chantal could end up on the south reaches of an outflow enhancing/shear reducing upper anticyclone located in relatively higher pressures between the paragraph P4 upper vortex....forecast southern fracture of paragraph P1 upper trough...and another forecast cut-off upper vortex coming in from the east (associated with paragraph P3 NW Atlatnic upper trough fragment).

 photo Jul_09_2013_TS_Chantal_Forecast_zps49d344c1.png
Figure 1: Forecast for Tropical Storm Chantal

Impact swath in Figure 1 is initialized with the tropical storm wind radius shwown at the 11 PM EDT NHC advisory...which is biased to the right side of the storm track due to Chantal's current rapid WNW motion. I keep the swath the same size thru the forecast with the assumption Chantal remains the same size (albeit I grow the swath a tad based on when I think she will reach max intensity). I also keep the swath biased to the right of my forecast track thru the forecast period because of her continued fast track early on...followed by the paragraph P4 upper vortex suppressing t-storms in her west half after she slows down later on. Note that at the end of my forecast (Saturday night)...my impact swath suggests Chantal will wrap in t-storms biased to the east as she escapes the paragraph P4 upper vortex and moves into southern reaches of more favorable upper anticyclone.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and attendant surface 1006 mb frontal depression is entering the upper-left corner of the above charts from western Canada and Montana.

P2...Cut-off upper trough continues slowly east and has finally moved into the Azores and the waters southwest. Mid-ocean surface trough formerly supported by eastern divergence of this cut-off has been absorbed into 1012 mb surface low's trough mentioned in paragraph P3. Remainder of upper troughing from this system is over the NE US in between NW Atlantic upper ridge and western US upper ridge...as well as over the Texas/Mexico area as an upper vortex due south of the western US upper ridge.

P3...Upper trough and surface frontal system over NE Canada with a 1004 mb surface center is moving into the high seas between Canada and Greenland (western convergence of this upper trough system supports 1023 mb surface ridge centered over southern Hudson Bay...and in the last 48 hrs a fragment of this upper trough has split southeastward about the northeast side of the paragraph P2 NW Atlantic upper ridge and into the NW Atlantic where its eastern divergence supports a surface trough attached to a 1012 mb low SE of Newfoundland). Low-level warm air advection ahead of the 1004 mb center is supporting an amplifying upper ridge east of Greenland just outside of the above charts. Upper trough moving into the NE Atlantic high seas in paragraph P2 of the previous discussion as a result has weakened into an NW-SE tilted upper trough within this upper ridge and due north of the Azores. Along the lengthy front extending south and west of the 1004 mb center is a 1010 mb frontal depression that has moved from Minnesota and into Lake Michigan in the last 24 hrs...and this depression is supported by split flow upper divergence between northerlies on the east side of the paragraph P2 western US upper ridge and mainstream mid-latitude westerlies.

P4...Upper vortex previously over the eastern Bahamas has retrograded westward into the western Bahamas while steered around the paragraph P2 NW Atlnatic upper ridge. As paragraph P9 highlights...upper divergence on the east side of this upper vortex is interacting with the north end of a surface tropical wave to produce storm activity in the vicinity of the Bahamas...the immensity of which caused this upper vortex to be breifly an area of interest in the NHC tropical weather outlook this past afternoon. This eastern upper divergence has atleast allowed for mid-level pressure falls with the current GFS model initialization showing vorticity as low as the 700 mb layer. The CMC computer model continues to develop a subtropical or tropical cyclone from this upper vortex as it retrogrades into the eastern Gulf of Mexico by 72 hrs. Still taking this CMC solution superficially at this time with no other models on board and with no signs of surface pressure falls.

P5...Surface ridge dominates much of the open Atlantic basin. A western 1025 mb center over Bermuda is supported by convergence between easterlies south of the paragraph P2 NW Atlantic upper ridge and southerlies on the east side of the paragraph P4 upper vortex. An eastern 1025 mb center SW of the Azores is supported by western convergence of paragraph P2 Azores cut-off upper trough. This surface ridge continues to have a northeastern lobe extending into western Europe supported by eastern convergence of upper ridge east of Greenland mentioned in paragraph P3.

...TROPICAL BELT DISCUSSION...
P6...T-storm activity below Gulf of Mexico upper ridging has considerably diminished in the last 24 hrs. Expect the upper ridging will become squaushed out by paragraph P4 upper vortex coming in from the east.

P7...Inverted upper trough previously in the western Caribbean is now over SE Mexico while persisting in relatively lower pressures south of the upper ridging mentioned in paragraph P6.

P8...Anticyclonic upper ridging in the eastern half of the Atlantic persists and remains expanded into the eastern two-thirds of the Caribbean (the enhanced poleward outflow at the west lobe of the Caribbean portion supports an increase in south-central Caribbean t-storms in the last 72 hrs). This upper ridging still has an upper anticyclone that has shifted east to a location SE of the Azores. This upper ridging also continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa. Embedded SW-NE oriented string of upper vorticity persists over W Europe's Iberia peninsula...through the Canary Islands...and into the waters NW of the Cape Verde Islands. Days ago the south end of this upper ridging (in conjunction with the south end of the paragraph P5 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air has ended as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart (see paragraph P7 of discussion #32 for development of low-latitude upper ridging over the Cape Verde Islands).

P9...Tropical wave previously over the north-central Caribbean is now moving into the western Caribbean. North end of this wave is interacting with eastern divergence of paragraph P4 upper vortex to produce activity in the vicinity of the Bahamas.

P10...Tropical wave previously south of the Cape Verde Islands is now southwest of the islands. It continues to have impressive storm activity while taking advantage of enhanced outflow of paragraph P8 low-latitude upper ridge axis over the Cape Verde Islands...as well as the moisture resurgence mentioned in the the latter part of paragraph P8. The storm activity appears to be sheared westward by the easterlies on the south side of the low-latitude upper ridge...but should the latent heat release of the t-storms locally inflate the upper ridging the upper flow directly over the tropical wave could become more anticyclonic and less shearing. If this tropical wave shows any signs of becoming better organized under less shearing...I will be upgrading it to a special feature on this blog.

P11...Satellite imagery suggests yet another impressive tropical wave is about to roll off Africa as marked in the lower-right of the above atmo chart. The storm activity appears to be sheared westward by the easterlies on the south side of the low-latitude upper ridge axis over the Cape Verde Islands mentioned in paragraph P8...but should the latent heat release of the t-storms locally inflate the upper ridging the upper flow directly over the tropical wave could become more anticyclonic and less shearing. If this tropical wave shows any signs of becoming better organized under less shearing...I will be upgrading it to a special feature on this blog.

2013 Atlantic Hurricane Season Birdseye Discussion #36

By: NCHurricane2009, 7:02 AM GMT on July 08, 2013

...MONDAY JULY 8 2013 3:00 AM EDT...
The south end of tropical wave Invest 95-L has developed into Tropical Storm Chantal while threatening the Lesser Antilles. Also monitoring another tropical wave currently south of the Cape Verde Islands...mentioned in paragraph P10...which is currently in the same favorable enviornment from which Chantal emerged.

Of note...it is unusual to have tropical cyclone activity east of the Lesser Antilles in early July. This indicates the potential for an active hurricane season ahead come August and September where a series of strong tropical waves emerging from Africa develop in the eastern open waters into potentially strong tropical cyclones.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_7_2013_2045Z_zpsdde56002.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1935Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_7_2013_2045Z_zpsc7b4b9de.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM CHANTAL...
South end of tropical wave Invest 95-L has evolved into Tropical Storm Chantal...while the status of the remainder of the wave is found in paragraph P9 in the tropical belt section below. My forecast versus the NHC's 11 PM EDT forecast is shown in Figure 1 below...and visit www.nhc.noaa.gov for latest NHC forecasts. Tropical storm watches and warnings have been raised for various islands in the Lesser Antilles...and latest status of these advisories can also be found at www.nhc.noaa.gov.

The NHC forecast track for the first 72 hrs agrees with the current and rapid forward motion of the storm of about 2.2 degrees latitude per 6 hrs (for instance using satellite imagery Chantal was centered around 45W at 5 PM EDT yesterday and was at 47.2W at the 11 PM EDT NHC advisory). Extrapolating the NHC recorded storm track in Figure 1 suggests the center of Chantal should land at 50W-10N (south of the NHC forecast) later today. Seeing that the steering surface ridge (paragraph P4) should remain in the same state for the first 72 hrs I see no reason to disagree with such an extrapolation thru 72 hrs. In all...this is why my forecast track develops a south bias relative to NHC but is at the same forward pace as the NHC's.

Chantal's future survival appears uncertain to me at this hour...reminding me of the early phases of Ernesto 2012 during last year's discussion #72. Like Ernesto...Chantal is moving rapidly westward...which makes the cyclonic circulation suscpetible to re-opening on her south side such that she quickly could lose her tropical cyclone status. Rapid westward motion may also indicate a strong trade wind flow into the ITCZ to her south...which could mean her low-level circulation competing with the ITCZ inflow. And also like Ernesto...the very recent 2 AM EDT NHC center fix suggests Chantal showing signs of her low-level center outrunning her favorable t-storm canopy and instead moving into Saharan dry air and an unfavorable inverted upper trough part of a SW-NE string of upper vorticity (both the dry air and SW-NE upper vorticity discussed further in paragraph P7). In fact using the GFS upper wind forecast and my track forecast position at 24 hrs...Chantal should be directly below the unfavorable inverted upper trough at 24 hrs. My forecast in Figure 1 shows Chantal crossing the southern Lesser Antilles as a 35 mph max wind tropical depression...but it is possible Chantal is a remnant tropical wave by that time.

My forecast in Figure 1 for now assumes Chantal survives the short-term unfavorable conditions...and instead has her recovering in the southern Caribbean by 48 and 72 hrs while forecast to be below the favorable Caribbean portion of the shear-reducing outflow-enhancing paragraph P7 upper ridging. Just after 72 hrs...I assume Chantal gets strong and vertically coupled enough to feel an initial northward pull from the paragraph P3 upper vortex. Models agree that the southern portion of a mid-latitude upper trough (not yet in the scope of the above birdseye charts) will dig far to the south and even cut-off such that the eastern divergence of the cut-off erodes the west side of the paragraph P4 low-level ridge such that even if Chantal stays a weak/shallow system that it will slow down and curve north anyway. I weaken Chantal at the end of my 5-day (120 hr) forecast as my position places Chantal in the midst of what models show to be a shearing upper westerly jet north of the Caribbean upper ridging and southeast of the paragraph P3 upper vortex.

 photo Jul_08_2013_TS_Chantal_Forecast_zpsb20cf86a.png
Figure 1: Forecast for Tropical Storm Chantal

Impact swath in Figure 1 is initialized with the tropical storm wind radius shwown at the 11 PM EDT NHC advisory...which also compliments the size of the compact t-storm canopy near Chantal's center. I actually dissipate the swath based on my forecast of weakening Chantal to a tropical depression...then re-generate another swath in the Caribbean assuming Chantal remains a compact but strengthening storm in the southern Caribbean (my swath size is maximum where I think Chantal has the potential to reach her max strength). I lean the swath to the right of my forecast track toward the end to reflect a system under westerly vertical shear.

...MID-LATITUDES DISCUSSION...
P1...Cut-off upper trough continues slowly east toward the Azores...and associated surface frontal cyclone has de-generated into a lenghty mid-ocean surface trough but is still supported by eastern divergence of the upper trough. Remainder of upper troughing from this system remains cut-off over the central US in between NW Atlantic upper ridge and western US upper ridge. This cut-off central US upper trough is undergoing a split...with the northern part of the split progressing across the Great Lakes and toward the NE US...and with the southern part of the split stationary over the Texas/Mexico area as an inverted upper trough.

P2...Upper trough over Greenland and far north Atlantic is scooting eastward into the NE Atlantic high seas...with eastern divergence of this upper trough supporting a 1004 mb frontal depression that has moved NE from the waters S of Greenland and into the waters E of Greenland in the last 24 hrs. Another upper trough and surface frontal system from northern Canada has crossed Hudson Bay and is currently in NE Canada with a 990 mb surface center (western convergence of this upper trough system supports 1022 mb surface ridge centered over southern Hudson Bay...and a fragment of this upper trough has split southeastward about the northeast side of the paragrahp P1 NW Atlantic upper ridge and into the NW Atlantic where its eastern divergence supports a new surface trough SE of Newfoundland). Along the lengthy front extending south and west of the 990 mb center is a developing frontal depression currently at 1010 mb over Minnesota supported by split flow upper divergence between northerlies on the east side of the paragraph P1 western US upper ridge and mainstream mid-latitude westerlies.

P3...Upper vortex previously north of Puerto Rico has retrograded westward into the eastern Bahamas while steered around the paragraph P1 NW Atlnatic upper ridge. As paragraph P8 highlights...upper divergence on the east side of this upper vortex is interacting with surface tropical wave to produce some activity east of the Bahamas. It appears the CMC computer model develops a subtropical or tropical cyclone from this tropical wave/upper vortex interaction when the system retrogrades into the eastern Gulf of Mexico by 72 hrs. Still taking this CMC solution superficially at this time with no other models on board.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1024 mb center midway between North Carolina and Bermuda remains stacked beneath the center of the paragraph P1 NW Atlantic upper ridge...which effectively makes this a deep-layered ridge center at this time. An eastern center over western Europe has become stacked beneath the center of western Europe upper anticyclone mentioned in paragraph P7.

...TROPICAL BELT DISCUSSION...
P5...The outflow of upper ridging continues to support t-storm activity across the western Gulf of Mexico. Associated surface trouhing...formerly supported byeastern divergence of the paragraph P1 central US upper trough...has dissipated as the central US upper trough is fracturing and weakening. With no more surface troughing...this activity can no longer organize into a tropical cyclone...and therefore this system has been removed from the NHC tropical weather outlook and is no longer classified as Invest 94-L on the Naval Reasearch Laboratory site. After 24 hrs...expect the upper ridging will become squaushed out by paragraph P3 upper vortex coming in from the east...finally bringing an end to the western Gulf t-storm activity.

P6...Inverted upper trough previously over the Florida peninsula has dissipated. Inverted upper trough previously in the central Caribbean is now in the western Caribbean while persisting in relatively lower pressures southeast of the upper ridging mentioned in paragraph P5.

P7...Anticyclonic upper ridging in the eastern half of the Atlantic persists and has expanded into the eastern two-thirds of the Caribbean (the enhanced poleward outflow at the west lobe of the Caribbean portion supports an increase in south-central Caribbean t-storms in the last 48 hrs). This upper ridging still has an upper anticyclone that recently moved into western Europe and out of the above charts...with relatively new anticyclonic upper ridging over and south of the Azores flaring up due to warm air advection ahead of what is now the paragraph P1 mid-ocean surface trough. Finally...this upper ridging continues to have a low-latitude axis present over the Cape Verde Islands extending into W Africa. Embedded SW-NE oriented string of upper vorticity persists from waters offshore of W Europe...through the Canary Islands...and into the waters W of the Cape Verde Islands and W of newly-formed tropical storm Chantal. Days ago the south end of this upper ridging (in conjunction with the south end of the paragraph P4 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude axis over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air has ended as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart (see paragraph P7 of discussion #32 for development of low-latitude upper ridging over the Cape Verde Islands).

P8...Tropical wave previously over the northeastern Caribbean is now in the north-central Caribbean interacting with eastern divergence of paragraph P3 upper vortex to produce an area of cloudiness east of the Bahamas.

P9...South end of tropical wave has become tropical storm Chantal while the remaining north end of this tropical wave is approaching the Lesser Antilles tonight with no activity as it is suppressed by paragraph P7 Saharan dry air and also by the SW-NE axis of upper vorticity also mentioned in paragraph P7.

P10...During discussion #33...Meteosat-9 satellite animation appeared to suggest the most impressive tropical wave of the season thus far was rolling off of Africa...with dominance later shifting to what is now tropical storm Chantal while this suspect tropical wave became inactive during discussions #34 and #35. NHC TAFB has added a tropical wave on their maps and due south of the Cape Verde Islands within the last 24 hrs...and for the sake of continuity from my previous discussions I will assume this is my suspect wave even though I am not 100% certain this is the case. This tropical wave has developed an impressive t-storm cluster this past afternoon which reveals a low-level cloud swirl as the t-storms have died off a bit this evening. Given that this tropical wave is taking advantage of the low shear and enhanced outflow of paragraph P7 upper ridging...in addition to the moisture resurgence toward Africa also mentioned in the latter part of paragraph P7...it is worth watching this tropical wave in addition to tropical storm Chantal.

2013 Atlantic Hurricane Season Birdseye Discussion #35

By: NCHurricane2009, 3:11 AM GMT on July 07, 2013

...SATURDAY JULY 6 2013 11:11 PM EDT...
Disturbance Invest 94-L in the western Gulf of Mexico continues to lack organization. See paragraph P5 for update statement on this system.

The south end of the tropical wave west of the Cape Verde Islands continues to stay organized and has been upgraded to disturbance Invest 95-L. With upper winds forecast to remain favorable for additional development....I have upgraded this tropical wave to a special feature on this blog due to high risk of tropical cyclone development at anytime within the next few days. See special feature section below for additional details on this situation.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_6_2013_1815Z_zps5c1d72c1.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1915Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_6_2013_1815Z_zpsac4eb5c7.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE INVEST 95-L...
Tropical wave west of the Cape Verde Islands continues west into the waters midway between the Cape Verdes and Lesser Antilles. In the last two days...the south end of the tropical wave has organized into an active 1009 mb surface low pressure spin perhaps while taking advantage of the low shear and enhanced outflow of the paragraph P7 upper ridging. This has caused the NHC to introduce the tropical wave into its outlook since yesterday evening and has caused the Naval Research Laboratory of the United States Navy to designate the tropical wave as disturbance Invest 95-L.

I will continue to assume that the tropical wave will not choke on Saharan dry air while embedded in the moisture resurgence toward Africa mentioned in the latter part of paragraph P7. Therefore it will be upper winds that will control the fate of the tropical wave...and based on the latest GFS model run this tropical wave will be below the favorable paragraph P7 tropical upper ridging for the next few days...especially as the embedded upper vorticity features also mentioned in paragraph P7 are shown to dissipate and as the upper ridging expands into the Caribbean in the wake of the retrograding paragraph P3 upper vortex. No computer models currently develop this tropical wave except the CMC which develops it into a tropical cyclone when it reaches the Caribbean/Gulf of Mexico region by 180 hrs (of course such long range solutions cannot be fully trusted). Expect the tropical wave to continue westward while steered by solid paragraph P4 surface ridge...and with the organization of the low pressure spin suggesting possible tropical cyclone formation at anytime within the next days...the Lesser Antilles should monitor the progress of this tropical wave.

...MID-LATITUDES DISCUSSION...
P1...Cut-off upper trough and surface frontal cyclone (currently 1013 mb) SE of Newfoundland is moving eastward toward the Azores. Remainder of upper troughing from this system remains cut-off over the central US in between NW Atlantic upper ridge and western US upper ridge.

P2...Upper trough and strong surface frontal cyclone previously SE of Greenland has mostly exited the picture from the upper-right of the above charts. Part of this upper trough remains over Greenland and far north Atlantic...with eastern divergence of this upper trough portion supporting a new 1000 mb depression south of Greenland along the front extending from the exited strong cyclone. Another upper trough and surface frontal system from northern Canada is currently crossing Hudson Bay with a 998 mb surface center over the northeast part of the bay.

P3...Upper vortex previously NE of the Lesser Antilles has retrograded westward to a position north of Puerto Rico while steered around the paragraph P1 NW Atlnatic upper ridge. Split easterly flow between the NW quad of this upper vortex and south half of the NW Atlantic paragraph P1 upper ridge supports a new surface trough near the eastern Bahamas with some cloud activity. CMC computer model suggests development of a subtropical or tropical cyclone from this surface trough/upper vortex when the system retrogrades into the eastern Gulf of Mexico by 96 hrs. This is the second time the CMC suggests development from this system (the first time was mentioned in paragraph P3 of discussion #30 on the morning of July 1). Taking this CMC solution superficially at this time with no other models on board.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1026 mb center midway between North Carolina and Bermuda remains stacked beneath the center of the paragraph P1 NW Atlantic upper ridge...which effectively makes this a deep-layered ridge center at this time. An eastern 1032 mb center near western Europe is supported by northeastern convergence of the western Europe upper anticyclone mentioned in paragraph P7.

...TROPICAL BELT DISCUSSION...
P5...As the statements in paragraph P1 above confirm...in the last days the south half of what was a large eastern North America upper trough has fractured into central US upper trough...and this upper trough has been weakening which has allowed the favorable tropical upper ridging to the south to expand northward and support active tropical weather in the western Gulf of Mexico. The favorable tropical upper ridging was becoming squeezed between paragraph P6 upper vorticity retrograding into Florida from the east and the central US upper trough to the northwest...but upper winds between now and 48 hrs are becoming more favorable again with the paragraph P6 upper vorticity dissipating and the central US upper trough evolving into a weakened TX/MX upper vortex. Despite the continued designation as Invest 94-L and continued mention of this disturbed weather in the NHC Tropical Weather Outlook...their are no signs of organization as the surface troughing is to the northwest of the thunderstorms. This is because the surface troughing like a non-tropical or subtropical system continues to be supported by eastern divergence of the central US upper trough. This places the surface trouhging in less favorable southwesterly shear ahead of the upper trough in addition to land interaction with the Texas and Mexico coasts. Perhaps the latent heat release of the thunderstorms could inflate the tropical upper ridging...with the strengthening outflow of the upper ridging supporting surface pressure falls that might allow new surface troughing to develop over open water. In the event the storms organize around any open water surface trough...I will upgrade this to a special feature. After 48 hrs...the favorable tropical upper ridging will become squaushed out by paragraph P3 upper vortex coming in from the east...finally bringing an end to this disturbance.

P6...Inverted upper trough previously over the east Florida coast and Cuba is now over the Florida peninsula and continues to weaken. Inverted upper trough in the central Caribbean persists in relatively lower pressures southeast of the tropical upper ridging mentioned in paragraph P5.

P7...Anticyclonic upper ridging in the eastern half of the Atlantic persists. Its upper anticyclone west of Portugal has moved into western Europe and out of the above charts...with a new upper ridge axis flaring up over the Azores due to warm air advection ahead of the 1013 mb low mentioned in paragraph P1. This upper ridging continues to extend southwest into the Lesser Antilles and now into the east half of the Caribbean...with low-latitude upper ridging also present over the Cape Verde Islands extending into W Africa. Embedded SW-NE oriented series of upper vorticity features persists from the Canary Islands to the waters W of the Cape Verde Islands. Days ago the south end of this upper ridging (in conjunction with the south end of the paragraph P4 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude structure over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air has ended as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart (see paragraph P7 of discussion #32 for development of low-latitude upper ridging over the Cape Verde Islands).

P8...Tropical wave previously heading into Central America was dropped from NHC TAFB maps within the last 24 hours...perhaps dissipating in the unfavorable southeastern convergnce of the paragraph P5 tropical upper ridging.

P9...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles has crossed the Lesser Antilles into the northeastern Caribbean. Currently the wave appears suppressed by swaths of dry Saharan air mentioned in paragraph P7.

P10...During discussion #33...Meteosat-9 satellite animation appeared to suggest the most impressive tropical wave of the season thus far was rolling off of Africa. In the last two days...it appears the dominance in this region now goes to the tropical wave Invest 95-L mentioned in the above special feature section while this suspect tropical wave has rapidly lost most of its activity. However I have marked this suspect tropical wave at a location over the Cape Verde Islands for the sake of continuity from my previous discussions...but if this suspect wave is not added in future NHC TAFB surface maps I will drop it from this blog.

2013 Atlantic Hurricane Season Birdseye Discussion #34

By: NCHurricane2009, 5:26 AM GMT on July 06, 2013

...SATURDAY JULY 6 2013 1:26 AM EDT...
Although computer model support for western Gulf of Mexico development has diminshed...the area of disturbed weather in this region has been upgraded to Invest 94-L by the Naval Research Laboratory of the United States Navy. See paragraph P5 for update statement on this situation.

Elsewhere...the south end of a tropical wave west of the Cape Verde Islands has quickly become organized in the last 24 hours. Although their is no computer model support for development...upper winds could be favorable for much of the next five days. Therefore I will upgrade this tropical wave to a special feature if it continues to stay organized in the next 24 hours. See paragraph P10 for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_5_2013_1745Z_zps44d1f6b5.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1919Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_5_2013_1745Z_zps6185c420.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Frontal cyclone and attendant upper trough SE of Greenland had exited the picture from the upper right of the above charts...but the upper trough leaves behind a cut-off SE of Newfoundland. 1010 mb frontal depression forming SE of Newfoundland in the previous discussion has moved NE and is currently 1012 mb while supported by eastern divergence of the cut-off upper trough. A new 1013 mb non-frontal surface depression has also developed well ENE of Bermuda while supported by split flow upper divergence at the boundary between the cut-off upper trough and NW Atlantic upper ridge mentioned later in this paragraph. Remainder of upper troughing from this system remains cut-off over the central US...with eastern divergence of this cut-off formerly supporting an eastern US frontal system that is now dissipating. NW Atlantic upper ridge was formerly supported by warm air advection ahead of what is now this dissipating surface front...but is now supported by warm air advection on the west side of the low-level ridge mentioned in paragraph P4.

P2...Upper trough and surface frontal cyclone previously in the high seas between Canada and Greenland is now SE of Greenland while its surface center has rapidly deepened to 978 mb in the last 36 hrs (this upper trough has temporarily merged with cut-off upper trough SE of Newfoundland mentioned in paragraph P1). Another upper trough and surface frontal system from northern Canada is currently crossing Hudson Bay with a 996 mb surface center over the northeast part of the bay.

P3...Upper vortex NE of the Lesser Antilles is beginning to retrograde westward around the paragraph P1 NW Atlantic upper ridge. Split northeasterly flow between the NW quad of this upper vortex ans SE quad of the NW Atlantic paragraph P1 upper ridge supported a flare up of t-storms last afternoon which has since wrapped cyclonically beneath the upper vortex and is now weakened this evening.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1028 mb center now midway between North Carolina and Bermuda has whirled anticylonically into a position beneath the center of the paragraph P1 NW Atlantic upper ridge...which effectively makes this a deep-layered ridge center at this time. An eastern greater-than-1028 mb center near western Europe is supported by northeastern convergence of the eastern Atlantic upper ridge mentioned in paragraph P7.

...TROPICAL BELT DISCUSSION...
P5...As the statements in paragraph P1 above confirm...in the last days the south half of what was a large eastern North America upper trough has fractured into a central US upper trough...and this upper trough has begun weakening which has allowed the favorable tropical upper ridging to the south to expand northward and support active tropical weather in the western Gulf of Mexico. However...paragraph P6 upper vorticity has retrograded westward toward the eastern Gulf...squeezing the favorable tropical upper ridging between that upper vorticity and the central US upper trough. Moreover...the surface troughing (which has recently developed a 1011 mb low) remains supported by by eastern divergence of the central US upper trough...which places the lowest surface pressures in unfavorable southwesterly vertical shear ahead of the upper trough. After 36 hrs from now...models show upper winds becoming more favorable with the paragraph P6 upper vorticity dissipated and the remainder of the paragraph P1 central US upper trough a weakened TX/MX upper vortex that perhaps could make a more subtropical rather than a fully tropical situation. Despite the recent upgrade to Invest 94-L and continued mention of this disturbed weather in the NHC Tropical Weather Outlook...Will not consider this a special feature on this blog until the system shows some signs of organization. As previously stated in paragraph P5 discussion #33...any tropical system that develops out of this would track NNW around the west side of the paragraph P4 ridge and into the Texas or east-facing Mexico coast as the eastern divergence of the paragraph P1 central US upper trough prevents the paragraph P4 ridge from re-building in the Gulf region.

P6...Upper vortex previously over the central Bahamas has retrograded westward about the paragraph P1 NW Atlantic upper ridge...and is currently over the east Florida coast and Cuba while weakening into an inverted upper trough. Another inverted upper trough has formed in the central Caribbean in relatively lower pressures southeast of the tropical upper ridging mentioned in paragraph P5.

P7...Anticyclonic upper ridging in the eastern half of the Atlantic persists. It still has an upper anticyclone west of Portugal/Europe now supported by warm air advection ahead of the 978 mb cyclone mentioned in paragraph P2 (and this upper anticyclonicity has a long...albeit somewhat broken...extension hundreds of miles southwestward toward the Lesser Antilles)...with relatively lower pressures south of the Portugal anticyclone supporting a SW-NE oriented series of upper vorticity features from the Canary Islands to the waters NW of the Cape Verde Islands. To the southeast of the upper vorticity is a low-latitude upper ridge over the Cape Verde Islands extending into W Africa.

P8...Tropical wave previously in the Mona Passage (midway between Puerto Rico and the Dominican Republic) is now in the south-central Caribbean heading into Central America. It is currently suppressed by dry Saharan air (seen by brown shading in lower part of above thermo chart) earlier advected from Saharan Africa by deep-layered easterly wind current on the south side of the paragraph P7 upper ridge and paragraph P4 surface ridge. The patch of dry air in the vicinity of this tropical wave in particular is currently supported by southeastern convergnce of the paragraph P5 tropical upper ridging.

P9...Tropical wave midway between the Cape Verde Islands and Lesser Antilles has made a defenite re-surgence in moisture against the dry air mentioned in paragraph P8 thanks to enhanced upper outflow of the paragraph P7 upper ridging supporting lift over the ocean surface.

P10...Tropical wave previously over the Cape Verde Islands is now west of the islands. It appears the south end of the tropical wave has rapidly organized into an active 1011 mb surface low pressure spin perhaps while taking advantage of the low shear and enhanced outflow of the paragraph P7 upper ridging. This has caused the NHC to introduce the tropical wave into its outlook this evening. I will assume the enhanced outflow of the paragraph P7 upper ridging will continue to trigger enough moistening lift over the ocean surface as to ward off the dry air mentioned in paragraph P8. Therefore it will be upper winds that will control the fate of the tropical wave...and based on the latest GFS model run this tropical wave will be below the favorable paragraph P7 tropical upper riding for the next 5 days (120 hrs) as it moves toward the Lesser Antilles (albeit the wave may encounter some of the less favorable paragraph P7 upper vorticity in the 24 to 48 hr timeframe after which time this upper vorticity diminshes). Therefore if this tropical wave conitnues to display an organized low pressure spin...I will be upgrading it to a special feature on my next blog post.

P11...During the previous discussion...Meteosat-9 satellite animation appeared to suggest the most impressive tropical wave of the season thus far was rolling off of Africa. This evening...it appears the dominance in this region now goes to the tropical wave mentioned in paragraph P10 while this suspect tropical wave has rapidly lost most of its activity. However I have marked this suspect tropical wave at a location SE of the Cape Verde Islands for the sake of continuity from my previous discussion...but if this suspect wave is not added in future NHC TAFB surface maps I will drop it from this blog.

2013 Atlantic Hurricane Season Birdseye Discussion #33

By: NCHurricane2009, 1:42 PM GMT on July 04, 2013

...THURSDAY JULY 4 2013 9:40 AM EDT...
Computer model support for western Gulf of Mexico development from tropical wave activity is once again reducing...see paragraph P5 for update statement on this situation. Elsewhere...a large swath of Saharan dry air in the tropical latitudes is likely to keep any additional tropical wave development suppressed in the short term.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_4_2013_0645Z_zps20c9a2c8.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0742Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_4_2013_0645Z_zps0c023154.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Frontal cyclone and attendant upper trough SE of Greenland continues eastward across the northeast Atlantic high seas...with a new 1010 mb frontal depression forming SE of Newfoundland while supported by split flow upper divergence at the boundary between the upper trough and NW Atlantic upper ridge mentioned later in this paragraph. Remainder of upper troughing from this system remains cut-off over the central US as a large-scale upper vortex...with eastern divergence of the upper vortex supporting 1019 mb surface frontal depression that has tracked northward from Indiana and into Michigan in the last 24 hrs. Western convergence of this upper vortex meanwhile supports surface ridging extending from the west side of the paragraph P4 Atlantic ridge and into the eastern half of the US. NW Atlantic upper ridge is currently supported by warm air adevction ahead of the aforementioned Michigan 1019 mb depression.

P2...Upper trough and surface frontal cyclone previously moving into NE Canada from Hudson Bay is now in the high seas between Canada and Greenland with a 993 mb surface center. Another upper trough and surface frontal system from northern Canada...new to this discusison...is currenlty over western Canada and is about to enter the upper-left corner of the above charts.

P3...Large upper trough in the open central Atlantic has re-closed into an upper vortex centered NE of the Lesser Antilles...and will soon begin retrograding westward around the building paragraph P1 NW Atlantic upper ridge.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1029 mb center near Bermuda is supported by SE convergence of paragraph P1 NW Atlantic upper ridge. An eastern 1025 mb center near the Azores is supported by western convergence of Canary Islands upper trough mentioned in paragraph P7.

...TROPICAL BELT DISCUSSION...
P5...As the statements in paragraph P1 above confirm...south half of large eastern North America upper trough has fractured into a central US upper vortex...and this upper vortex will begin weakening...which will allow the favorable upper ridging in the western Caribbean area to expand northward in its wake and perhaps support western Gulf of Mexico tropical development from the tropical wave activity previously mentioned in discussion #32 paragraph P5. All tropical waves in this area have transitioned into Gulf of Mexico surface troughs supported by eastern divergence of the paragraph P1 central US upper vortex...with the surface troughs and associated t-storms continuing to be mentioned in the NHC Tropical Weather Outlook. NAVGEM and GFS models have backed off their support...with the CMC no longer showing development. In the next 24 hrs...the paragraph P6 upper vortex will retrograde westward into the region and the favorable upper winds. After 72 hrs...models shows upper winds becoming favorable again with the paragraph P6 upper vortex dissipated and the remainder of the paragraph P1 upper vortex a weakened TX/MX upper vortex that perhaps could make a more subtropical rather than a fully tropical situation. Due to the forecast pause in favorable upper winds between 24 and 72 hrs...still am skeptical of development potential....and therefore I will not upgrade this to a special feature until their are signs of organization when this system moves over the western Gulf waters. As previously stated in paragraph P5 discussion #32...any tropical system that develops out of this would track NNW around the west side of the paragraph P4 ridge and into the Texas or east-facing Mexico coast as the forecast eastern divergence of the south fracture of the paragraph P1 upper vortex keeps the paragraph P4 ridge from re-building in the Gulf region.

P6...Upper vortex north of Hispaniola has moved westward into the central BAhamas...and over the next 24 hrs will continue westward while steered by south side of paragraph P1 NW Atlantic upper ridge.

P7...Anticyclonic upper ridge in the eastern half of the Atlantic persits. It still has a building upper anticyclone west of Portugal supported by warm air advection ahead of the paragraph P1 cyclone SE of Greenland (and this anticyclone has a long extension hundreds of miles southwestward toward the Lesser Antilles)...with relatively lower pressures south of the building Portugal anticyclone triggering a new SW-NE oriented upper trough from the Canary Islands to the waters W of the Cape Verde Islands. To the southeast of the upper trough is a new low-latitude upper ridge over the Cape Verde Islands extending into W Africa.

P8...Tropical wave previously crossing the Lesser Antilles is now in the Mona Passage midway between Puerto Rico and the Dominican Republic. It is leaving behind unfavorable dry Saharan air (seen by brown shading in lower part of above thermo chart) earlier advected from Saharan Africa by deep-layered easterly wind current on the south side of the paragraph P7 upper ridge and paragraph P4 surface ridge. Instead it is now entering moistened air supported by eastern divergence of paragraph P6 upper vortex.

P9...Tropical wave previously SW of the Cape Verde Islands is now midway between the Cape Verdes and Lesser Antilles and was earlier becoming suppressed by dry Saharan air mentioned in paragraph P8 above. However it seems to have made a re-surgence in moisture...mainly in its east half...due to enhanced poleward upper outflow of the paragraph P7 Cape Verde Islands low-latitude upper ridge supporting lift over the ocean surface.

P10...Tropical wave previously east of the Cape Verde Islands is now over the islands. Despite being embedded in the moisture re-surgence described in paragraph P9 above...it continues to be inactive...perhaps as it is competing with the low-level inflow of the impressive paragraph P11 tropical wave to its east.

P11...Most impressive tropical wave of the season thus far is beginning to roll off of Africa this morning with a large curved band of t-storms. Even though it is moving into the favorable and moistened enviornment described in paragraph P9 above...their is no current computer model support for development. Unfavorable factors that lie ahead include the upper vorticity of the SW-NE paragraph P7 upper trough and potentially the dry Sahran air mentioned in paragraph P9.

2013 Atlantic Hurricane Season Birdseye Discussion #32

By: NCHurricane2009, 2:20 PM GMT on July 03, 2013

...WEDNESDAY JULY 3 2013 10:20 AM EDT...
Computer model support for western Gulf of Mexico development from tropical wave activity is returning...see paragraph P5 for update statement on this situation. Elsewhere...a large swath of Saharan dry air in the tropical latitudes is likely to keep any additional tropical wave development suppressed.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_3_2013_0645Z_zpsafebbf18.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0730Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_3_2013_0645Z_zps048d68c4.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Frontal cyclone and attendant shortwave upper trough SSW of Greenland in the previous discussion is now SE of Greenland while it has deepened further to 984 mb (western convergence of the shortwave upper trough supports surface 1022 mb ridge over eastern Newfoundland). Remainder of upper troughing from this system remains cut-off over the eastern US and Gulf of Mexico as a large-scale upper vortex...with eastern divergence of the upper vortex supporting 1015 mb surface frontal depression that has tracked northward from Tennessee and into Indiana in the last 24 hrs. Western convergence of this upper vortex meanwhile supports central US surface ridge that has a 1021 mb northeastward extension across the Great Lakes area (this extension is supported by western convergence of paragraph P2 upper trough). NW Atlantic upper ridge is currently supported by warm air adevction ahead of the aforementioned Indiana 1015 mb depression.

P2...Upper trough and surface frontal cyclone from northern Canada...new to this discussion...has recently crossed Hudson Bay and into NE Canada.

P3...Large upper vortex that has persisted in the open central Atlantic for the last several days has opened into an upper trough while temporarily linking with paragraph P1 upper trough SE of Greenland. Associated nearby surface troughing mentioned in the previous discussion has dissipated. Expect this system to re-close into an upper vortex that subsequently retrogrades westward around the building paragraph P1 NW Atlantic upper ridge.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1028 mb center just east of Bermuda is supported by SE convergence of paragraph P1 NW Atlantic upper ridge. An eastern 1028 mb center near the Azores is supported by northeastern convergence of east Atlnatic upper ridge mentioned in paragraph P7.

...TROPICAL BELT DISCUSSION...
P5...As the statements in paragraph P1 above confirm...south half of large eastern North America upper trough has fractured and will begin weakening...which will allow the favorable upper ridging in the area to expand northward in its wake and perhaps support western Gulf of Mexico tropical development from the tropical wave previously mentioned in discussion #31 paragraph P4 and discussion #30 paragraph P5 (this tropical wave is currently over SE Mexico). In addition... the tropical wave in discussion #31 paragraph P6 has joined this area from the western Caribbean...with both tropical waves and associated t-storms becoming introduced into the NHC Tropical Weather Outlook in the last 24 hrs. NAVGEM and GFS models have been weakly suggestive of western Gulf development since discussion #30 paragraph P5...with the CMC now onboard (the CMC in its last several runs also has been showing another seperate north-central Gulf surface low spinning up...but I consider this non-tropical and not associated with this situation while supported by eastern divergence of south fracture of paragraph P1 upper trough). Since discussion #30 paragraph P5...GFS has been consistent with the upper winds being favorable in the timeframe that is between now and 48 hrs...after which time the paragraph P6 upper vortex retrogrades westward into the region to suppress the favorable upper winds. After 96 hrs...GFS shows upper winds becoming favorable again with the paragraph P6 upper vortex dissipated and the remainder of the paragraph P1 upper trough a TX/MX upper vortex that perhaps could make a more subtropical rather than a fully tropical situation. Due to the forecast pause in favorable upper winds between 48 and 96 hrs...still am skeptical of development potential....and therefore I will not upgrade this to a special feature until their are signs of organization when this system moves over the western Gulf waters. As previously stated in paragraph P5 discussion #30...any tropical system that develops out of this would track NNW around the west side of the paragraph P4 ridge and into the Texas coast as the forecast eastern divergence of the south fracture of the paragraph P1 upper trough keeps the paragraph P4 ridge from re-building in the Gulf region.

P6...Upper vortex persists north of Hispaniola...and over the next 48 hrs will retrograde westward while steered by south side of paragraph P1 NW Atlantic upper ridge.

P7...Anticyclonic upper ridge in the eastern half of the Atlantic...mentioned in paragraph P7 of the previous discussion...has undergone a few changes. It now features a building upper anticyclone west of Portugal supported by warm air advection ahead of the paragraph P1 984 mb cyclone...with relatively lower pressures south of the building anticyclone triggering a new SW-NE oriented inverted upper trough from the Canary Islands to the waters W of the Cape Verde Islands. To the southeast of the inverted upper trough is a new low-latitude upper ridge over the Cape Verde Islands extending into W Africa.

P8...Tropical wave previously en route to the Lesser Antilles will be crossing the islands and into the eastern Caribbean later today. It is currently below a favorable SW extension of anticyclonic eastern Atlantic upper ridge mentioned in paragraph P7 above...but is suppressed by unfavorable dry Saharan air (seen by brown shading in lower part of above thermo chart) earlier advected from Saharan Africa by deep-layered easterly wind current on the south side of the upper ridge and south side of the paragraph P4 surface ridge.

P9...Tropical wave SW of the Cape Verde Islands was becoming suppressed by dry Saharan air mentioned in paragraph P8 above...but it seems to have made a re-surgence in moisture due to enhanced poleward upper outflow of the paragraph P7 Cape Verde Islands low-latitude upper ridge supporting lift over the ocean surface.

P10...Tropical wave previously rolling off the west African coast has been added to NHC TAFB maps in the last 24 hrs to the east of the Cape Verde Islands. Despite being embedded in the moisture re-surgence described in paragraph P9 above...it has seen a recent decrease in its cloudiness.

2013 Atlantic Hurricane Season Birdseye Discussion #31

By: NCHurricane2009, 1:18 PM GMT on July 02, 2013

...TUESDAY JULY 2 2013 9:30 AM EDT...
Whatever weak computer model support for western Gulf of Mexico development from tropical wave activity is diminshing. And with a large swath of Saharan dry air building westward in the tropical latitudes...all should be quiet in the Atlantic tropics during the next few days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_2_2013_0615Z_UPDATED_zps095c6b5c.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0730Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_2_2013_0615Z_UPDATED_zps51546be5.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Large upper trough spanning eastern North America and Gulf of Mexico has split into a few features in the last 36 hrs. Frontal cyclone that was previously south of Greenland in the previous discussion is heading into western Europe while its cool air advection on its back side has carved out a supporting shortwave upper trough (frontal cyclone's upper trough marked with blue-dashed line...and frontal cyclone's warm front also marked...in upper-right corner of above atmo chart). Frontal cyclone over eastern Canada in the previous discussion has ejected northeastward into the Atlantic high seas SSW of Greenland while deepening to 999 mb...and it too with its cool air advection had carved out its own supporting shortwave upper trough (western convergence of this shortwave supports surface 1027 mb ridge over eastern Canada to the SE of Hudson Bay). Remainder of upper troughing is cut-off over the eastern US and Gulf of Mexico as a large-scale upper vortex...with eastern divergence of the upper vortex supporting 1012 mb surface frontal depression currently over Tennessee. Western convergence of this upper vortex meanwhile supports 1023 mb ridge building into central North America as shown by the red-zig-zag line in the upper-left corner of the above atmo chart. NW Atlantic upper ridge is currently supported by warm air adevction ahead of the aforementioned Tennesse 1012 mb depression.

P2...Large upper vortex persists in the open central Atlantic. Surface trough southeast of Bermuda persists while supported by split flow upper divergence between westerlies flowing into this upper vortex and easterlies flowing into the Lesser Antilles-Bermuda upper vortex mentioned in paragraph P5. Another surface trough is beneath the east side of the upper vortex while supported by the vortex's eastern divergence. The central Atlantic upper vortex in the days ahead is expected to retrograde westward around the building NW Atlantic upper ridge mentioned in paragraph P1 above.

P3...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1030 mb...is near the western Azores. It is supported by southeastern convergence of NW Atlantic upper ridge mentioned in paragraph P1 as well as northeastern convergence of east Atlnatic upper anticyclonic ridge mentioned in paragraph P7.

...TROPICAL BELT DISCUSSION...
P4...Tropical wave previously over the western Caribbean has split into a southern fragment that has evolved into an eastern Pacific tropical disturbance...and a northern fragment currently over interior SE Mexico. This tropical wave is currently suppressed by non-divergent region and westerly shear directly south of the paragraph P1 upper trough.

P5...Upper vortex previously midway between the Lesser Antilles and Bermuda is retrograding westward about the paragraph P1 NW Atlnatic upper ridge...and is currently located north of Hispaniola.

P6...Tropical wave previously in the eastern Caribbean is now in the north-central Caribbean region. T-storm activity in its vicinity is enhanced by divergent northerly flow at the boundary between the SW side of the paragraph P5 upper vortex and tropical upper ridging from the west previously mentioned in discussion #30 paragraph P5.

P7...Tropical wave previously midway between the Lesser Antilles and the Cape Verdes is now en route to the Lesser Antilles. It is currently below a favorable SW extension of anticyclonic eastern Atlantic upper ridge...but is suppressed by unfavorable dry Saharan air (seen by brown shading in lower-right of above thermo chart) advected from Saharan Africa by deep-layered easterly wind current on the south side of the upper ridge and south side of the paragraph P3 surface ridge.

P8...Tropical wave previously SE of the Cape Verde Islands is now SW of the islands. It too is suppressed by dry Saharan air mentioned in paragraph P7 above.

P9...Tropical wave is about to roll off the west African coast as marked in lower-right corner of above atmo chart. Although it has an associated t-storm cluster...expect it to also choke on dry Saharan air mentioned in paragraph P7 above.

2013 Atlantic Hurricane Season Birdseye Discussion #30

By: NCHurricane2009, 1:34 PM GMT on July 01, 2013

...MONDAY JULY 1 2013 9:30 AM EDT...
Tropical wave crossing the Lesser Antilles has been removed from the National Hurricane Center tropical weather outlook while moving below unfavorable upper winds (see paragraph P7 for update statement on this wave). Tropical wave entering the western Caribbean has also been removed from the National Hurricane Center Tropical Weather Outlook...although their is light computer model support suggestive of development potential when the wave later reaches the western Gulf of Mexico (see paragrah P5 for update statement on this wave).

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jun_30_2013_2345Z_zps16c282b2.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0128Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jun_30_2013_2345Z_zpse0567d04.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Great Lakes upper vortex mentioned in paragraph P1 of the previous discussion...Gulf of Mexico upper vortex mentioned in paragraph P7 of the previous discussion...and upper trough crossing Hudson Bay in paragraph P2 of the previous discussion have all merged into one large upper trough spanning eastern North America and the Gulf of Mexico. Eastern divergence of this upper trough supports a deepening 998 mb frontal cyclone that has moved from the US/Canada border and into the Atlantic high seas south of Greenland in the past day. Weaker east Canada frontal cyclone...mentioned in paragraph P2 of the previous discussion and currently at 1003 mb...is also supported by eastern divergence of this upper trough. Western convergence of this upper trough meanwhile supports 1023 mb ridge building over the southern Hudson Bay region as well as a surface ridge building into central North America as shown by the red-zig-zag line in the upper-left corner of the above atmo chart. NW Atlantic upper ridge is supported by warm air adevction ahead of the 998 mb cyclone's lengthy front...which continues to have a relatively new extension near the the SE US coast.

P2...Upper trough previously SE of Greenland continues eastward into the NE Atlatnic high seas and into western Europe.

P3...Large upper vortex persists in the open central Atlantic. A new surface trough southeast of Bermuda and west of this upper vortex is supported by split flow upper divergence between westerlies flowing into this upper vortex and easterlies flowing into the Lesser Antilles-Bermuda upper vortex mentioned in paragraph P6. The central Atlantic upper vortex in the days ahead is expected to retrograde westward around the building NW Atlantic upper ridge mentioned in paragraph P1 above...and the latest CMC computer model run suggests potential subtropical or tropical cyclone development from this upper vortex and perhaps the surface trough as it approaches the western Bahamas and south Florida by 180 hrs. Taking this CMC solution superficially at this time with no other models on board.

P4...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1033 mb...is near the western Azores. It is supported by southeastern convergence of NW Atlantic upper ridge mentioned in paragraph P1. Westward extension of this ridge reaching into the Gulf of Mexico has been eroded away by eastern divergence of paragraph P1 upper trough in the last 24 hrs.

...TROPICAL BELT DISCUSSION...
P5...Tropical wave continues moving into the western Caribbean. Upper ridging from the southwest continues to make upper winds a bit more favorable and enhance t-storms in the vicinity of the wave and over Central America. Another batch of t-storms is over western Cuba...the Yucatan Channel...and the NE Yucatan...supported by divergent southwesterly flow ahead of the paragraph P1 upper trough. The south end of this upper trough is forecast by models to fracture and then weaken...allowing the favorable upper ridging to expand northward in its wake and perhaps support western Gulf of Mexico tropical development from this wave as weakly suggested by the latest NAVGEM and GFS. The pinnacle of these favorable upper winds in the latest GFS is at 96 hrs...after which time the model shows the paragraph P6 Lesser Antilles-Bermuda upper vortex retrograde westward and into the region and suppress the favorable upper winds. Therefore I am currently skeptical of any development from this tropical wave...but if it were to occur the tropical system would track NNW around the west side of the paragraph P4 ridge and into the Texas coast as the forecast eastern divergence of the south fracture of the paragraph P1 upper trough keeps the paragraph P4 ridge from re-building in the Gulf region.

P6...Upper vortex persists midway between the Lesser Antilles and Bermuda.

P7...Tropical wave crossing the Lesser Antilles is currently in the eastern Caribbean. The tropical wave is currenlty inactive while suppressed by non-divergent region directly south of the paragraph P6 Bermuda-Lesser Antilles upper vortex.

P8...Tropical wave previously SW of the Cape Verde Islands is now midway between the Lesser Antilles and the Cape Verdes. It is currently below a favorable SW extension of anticyclonic eastern Atlantic upper ridge...but is suppressed by unfavorable dry Saharan air (seen by brown shading in lower-right of above thermo chart) advected from Saharan Africa by deep-layered easterly wind current on the south side of the upper ridge and south side of the paragraph P4 surface ridge.

P9...Vigorous tropical wave rolling off of the west African coast was finally added to NHC TAFB maps 00Z this early morning at a location SE of the Cape Verde Islands. Despite its early impressivenes...it has lost t-storm activity as it begins ingesting the dry air mentioned in paragraph P8 above.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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