NCHurricane2009's Blog

2015 Atlantic Hurricane Season Birdseye Discussion #8

By: NCHurricane2009, 2:23 AM GMT on May 27, 2015

...TUESDAY MAY 26 2015 10:24 PM EDT...
Warm air advection ahead of the slow-moving central US 1005 mb frontal cyclone marked in the atmospheric features chart below...the same system that has caused flooding and severe weather in Oklahoma and Texas over the last few days...has amplified an upper ridge over the eastern US and western Atlantic (marked as a blue-zig-zag line). Eastern convergence of this upper ridge supports a 1031 mb western Atlantic surface ridge...effectively creating a strong deep-layered ridge in the region that has cut-off the southern part of a central Atlantic frontal system into an upper vortex centered at 27.5N-57.5W (marked as a blue L). The formation of this upper vortex has resulted in a subtropical disturbance southeast of Bermuda that has become better organized in the last few hours.

None of the computer models develop this system into a subtropical or tropical cyclone. The southern part of the central Atlantic surface frontal zone could organize into a surface low beneath the upper vortex in the next 24 hours...as suggested by the European (ECMWF) model. Therefore the next 24 hours are the most favorable for development. Unfavorable thermodynamic conditions for this system include some dry air caused by western convergence of the upper vortex and the fact that this system is just north of the 26 deg C isotherm...although cold upper air associated with the upper vortex could help de-stabilize the system depsite the sub-26 deg C water. However the most recent satellite frames show weakening clouds near the center of the upper vortex and therefore their are no signs of development. After 24 hours all models agree that this system weakens to an inverted surface trough traveling westward on the south side of the 1031 mb western Atlantic ridge...exposing this system to unfavorable northerly shear and upper convergence on the west side of the upper vortex.

Unless the above-discussed subtropical disturbance southeast of Bermuda shows signs of development within the next 24 hours...this will be my last update on this blog until the start of Atlantic Hurricane Season on June 1.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1940Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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 temperature isotherms at http://www.nhc.noaa.gov/satellite.php...the site from which the above thermo chart is generated from...are currently outdated. Therfore I have approximated the 26 deg C isotherm in the above chart using the sea-surface temperature maps available at www.wuwnderground.com/tropical. 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).

2015 Atlantic Hurricane Season Birdseye Discussion #7A (Special Update)

By: NCHurricane2009, 9:51 PM GMT on May 10, 2015

...SUNDAY MAY 10 2015 5:51 PM EDT...
The final advisory on Ana from the National Hurricane Center has been issued as Ana has weakened to a decaying inland tropical depression. Heavy rains are possible across eastern North Carolina...southeast Virginia...southeast Maryland...and southern Delaware over the next 48 hours from the remnants of Ana. With no other threats of tropical activity in the Atlantic basin...have stopped doing daily updates on this blog. Will resume daily updates at the start of the Atlantic Hurricane Season on June 1.

2015 Atlantic Hurricane Season Birdseye Discussion #7

By: NCHurricane2009, 11:31 AM GMT on May 10, 2015

...SUNDAY MAY 10 2015 7:30 AM EDT...
Since the previous discussion Ana transitioned into a fully tropical storm. The center of the tropical storm has just made landfall midway between Myrtle Beach South Carolina and the North Carolina-South Carolina border. Tropical storm warnings remain in effect for a portion of the South and North Carolina coasts...but will likely get dropped later today as Ana moves further inland and weakens to a tropical depression. See special feature section below for additional detials on Ana. Visit www.nhc.noaa.gov for up to the minute latest information on Ana...including the latest watches and warnings.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z and 0725Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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 ANA...
Current prognosis...Yesterday morning Ana went from having t-storm bands around the center to having a central core of thunderstorms that featured some warm core anticyclonic outflow tucked below its parent upper vortex. This prompoted an upgrade from subtropical to tropical status. Ana's vertical warm core structure (surface spin and upper-level anticyclonic outflow) is not as tall as a typical tropical cyclone...therefore making it less sensitive to the current northwesterly shear being imparted by northwesterly upper winds between the west side of its parent upper vortex (marked by blue L to the right of Ana in the above atmospheric features chart) and east side of upper-riding over the eastern US (marked by blue-zig-zag line). However there have been some signs that Ana has been struggling a bit with the shear with its upper anticyclonic outflow being biased to the south...and with its thunderstorm core being a bit lopsisded to the south and east quadrants as seen on satellite and radar. After reaching a peak of 60 mph max sustained winds...Ana weakened quickly to 45 mph max sustained winds just prior to landfall while crossing a coastal cool shelf of waters well below 26 deg C...and will weaken further to a tropical depression and perhaps a remnant low later today as she inches further inland.

Atmospheric Outlook for the Forecast Period...Ana will continue northward and then accelerate northeastward in the flow between the 1031 mb Atlantic ridge to the east and approaching 1005 mb frontal cyclone from the west. After Ana weakens to a remnant low over the mid-Atlantic United States...the frontal cyclone will eventually absorb it.

Thermodynamic Outlook for the Forecast Period...The cooler shelf of waters well below 26 deg C located along the SE US shoreline weakened Ana from 60 to 45 mph max sustained winds just before she made landfall this morning. Now that Ana is moving ashore...sea surface temps are no longer important in the strength of Ana.



Track Forecast...Ana has been following the previous forecast track...but has been moving a bit faster than previously shown...making landfall about 3 to 6 hours ahead of schedule. The lastest NHC forecast track shown above shows Ana moving thru eastern North Carolina by 2 AM Sunday...also about 3 to 6 hours ahead of schedule from the previous forecasts. Therefore I agree with the above NHC track forecast.

Intensity Forecast...Even though the current intensity of Ana is listed as 45 mph max sustained winds...surface obs from National Weather Service stations in the landfall area have not shown such winds. Therefore if there are any tropical storm winds left in the circulation...they are probably occuring in intermittent spurts in offshore rain bands. The NHC intensity forecast keeps Ana as a tropical depression thru Monday in anticipation that offshore bands could produce depression force winds...but since Ana has been struggling to show tropical depression or tropical storm force winds presently...I believe it will weaken to a remnant low by tonight.

Impact Forecast...My impact swath in the above forecast graphic is the size of the current 5 AM EDT NHC tropical storm wind field. The reason impact statement (a) in the above graphic says tropical storm winds "possible" instead of "imminent" is due to the lack of tropical storm winds and gusts in current National Weather Service stations in the landfall area. The main threat from Ana will be flash flooding from heavy downpours in her rain bands...and the timing of this rainfall is in impact statement (b). I have expanded impact statement (b) to include southeast Virginia...SE Maryland...and southern Delaware since Ana is showing some impressive radar rain bands in the east half of the circulation and therefore Ana's current moisture field is impressive enough that Ana's rains could last even as it becomes a remnant low moving through the coastal mid-Atlantic US.

2015 Atlantic Hurricane Season Birdseye Discussion #6

By: NCHurricane2009, 5:46 AM GMT on May 09, 2015

...SATURDAY MAY 9 2015 1:46 AM EDT...
Subtropical Storm Ana has strengthened this afternoon and evening while continuing to pinwheel just offshore of the Carolina coast. Tropical storm watches and warnings are in effect for a portion of the South and North Carolina coasts. See special feature section below for additional details on Ana. Visit www.nhc.noaa.gov for up to the minute latest information on Ana...including the latest watches and warnings.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0128Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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...SUBTROPICAL STORM ANA...
Current prognosis...Ana remains structured as a classical subtropical storm with the surface center centered below a parent upper vortex...with cold air from the upper vortex helping to de-stabilize the atmosphere and hence allow for shower and t-storm activity in the circulation. Within the last few hours the t-storm activity went from less organized clumps to a well organized curved band covering the north half of the circulation...and aircraft reconaissance has confirmed that Ana has strengthened to 60 mph maximum sustained winds...more than previously anticipated. 24 hours ago it appeared Ana was drifting westward on the north side of its parent upper vortex. Shortly thereafter the upper vortex whirled over the surface center...causing the system to stall. Upper-level wind barbs in the above atmospheric features chart directly above Ana are becoming increasingly anticyclonic...suggesting that Ana's t-storm latent heat release maybe punching out a vertical warm core within its cold core parent upper vortex...which could mean that Ana may become fully tropical soon. The formation of this warm core and upper-anticyclonic flow seems to have recently displaced the cold core center of the parent upper vortex just northeast of Ana's surface center...as indicated by the location of the blue L next to Ana in the above atmospheric features chart. As of 11 PM EDT National Hurricane Center advisory fixed the surface center at 32.1N-77.4W...indicating an overall northward motion of 0.5N latitude per 24 hours when comparing to yesterday's 11 PM EDT center fix.

Atmospheric Outlook for the Forecast Period...1031 mb surface ridge cell over eastern Canada...supported by western convergence of north-central Atlantic upper vortex (marked as blue L in top-center of above atmsopheric features chart)...will dive south...effectively strengthening the Atlantic surface ridge east of Ana. This will add a westward component to the storm track as Ana slides northward on the west side of this ridge. During the later part of the forecast period...Ana will then turn and accelerate northeastward out ahead of an upper trough and surface frontal cyclone forecast to move thru the eastern US (currently this frontal cyclone is a 1001 mb depression over the SW US located in the top-left of the above atmospheric features chart).

Thermodynamic Outlook for the Forecast Period...Ana is currently over a sub-26 deg C portion of the Gulf stream warmth. Despite water temps just below 26 deg C...Ana is able to fire showers and t-storms due to de-stabilizing cold air of its parent upper vortex as mentioned in the above current prognosis section. Dry air caused by western convergence of its parent upper vortex was wrapping into the circulation and breaking up the t-storm activity...but recently it appears the aformenetioned instability has finally allowed Ana to mix out this dry air and begin a strenghtening trend. Therefore the only unfavorable thermodynamic parameter is the cooler shelf of waters well below 26 deg C located along the SE US shoreline...which could have a negative effect on Ana as she approaches landfall on Sunday.



Track Forecast...The latest computer model runs and the above forecast track are all north and east adjustments from 24 hours ago...because as noted in the above current prognosis section Ana drifted a half a degree north in latitude instead of following previous forecasts which suggested that Ana would initially drift west on the north side of its parent upper vortex. I agree with the 24-hour (8 PM Sat) forecast position from NHC's 11 PM EDT package since this agrees with the current 0.5N-latitude-per-day pace coupled with the expected strengthening of the Atlantic surface ridge which will add a west component to the track as noted in the above atmospheric outlook section. I also agree with the 48 and 72 hour forecast track positions which is in alignment with what is now a tight computer model consensus.

Intensity Forecast...I have significantly increased my intensity forecast from 24 hours ago and am currently above the latest NHC intensity guidance...predicting that Ana will become a 70 mph max sustained wind tropical storm just below hurricane force within the next 24 hours for the following three reasons. First...the curved band of t-storms in the north half of the circulation continues to expand...giving this system a more impressive appearance with each new satellite frame. Second...Ana appears to be mixing out the dry air as noted in the above thermo outlook section. Third...I previously thought Ana would never make the transition to fully tropical status and get exposed to northerly shear on the west side of its parent upper vortex as the vortex slid eastward and away. Instead...as noted in the above current prognosis section...Ana appears to be generating a vertical warm core...and so now I believe it will become fully tropical and punch out a good chunk of the upper vortex...with the warm core generating a favorable upper anticyclone that could merge with and get re-enforced by the upper ridge wave currently marked by the blue-zig-zag line over the eastern US in the above atmospheric features chart. However I also believe Ana will weaken from its peak strength just prior to landfall due to the coastal cool shelf of waters noted in the above thermo outlook section.

Impact Forecast...My impact swath in the above forecast graphic is based on extrapolating the 11 PM EDT NHC tropical storm wind field along my forecast track for the portion of the track where Ana is a subtropical storm.

2015 Atlantic Hurricane Season Birdseye Discussion #5

By: NCHurricane2009, 5:08 AM GMT on May 08, 2015

...FRIDAY MAY 8 2015 1:08 AM EDT...
The well-organized subtropical surface low centered just offshore of the southeastern United States has intensified into Subtropical Storm Ana...kicking off the 2015 Atlantic Hurricane Season to an early start. Tropical storm watches have been issued for a portion of the South and North Carolina coasts. See special feature section below for additional detials on Ana. Visit www.nhc.noaa.gov for up to the minute latest information on Ana...including the latest watches and warnings.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0131Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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...SUBTROPICAL STORM ANA...
Current prognosis...Subtropical surface low Invest 90-L was upgraded to Subtropical Storm Ana as of 11 PM EDT as aircraft reconaissance from earlier this afternoon measured a sizeable tropical storm wind field...followed by flare ups of showers and t-storms near the center that have occurred since the reconaissance mission. System is structured as a classical subtropical storm with the surface center centered below a parent upper vortex...with cold air from the upper vortex helping to de-stabilize the atmosphere and hence allow for clumps of showers and t-storms to flare up near the surface center. The 11 PM EDT National Hurricane Center advisory fixed the surface center at 31.5N-77.6W...with satellite animation suggesting that the surface center is drifting westward toward 78W.

Atmospheric Outlook for the Forecast Period...Ana is expected to drift westward for the first 48 hours while steered by the north side of its parent upper vortex...which will be sliding eastward and away from Ana thru the forecast period. Another thing that will help this westward drift will be the strengthening of the 1026 mb Atlantic surface ridge which will gain support from the western convergence of north-central Atlantic upper vortex (marked as blue L in top-center of above atmospheric featuers chart). Then by 72 and 96 hours...Ana will turn and accelerate northward between the west side of the Atlantic surface ridge and out ahead of an upper trough and surface frontal cyclone forecast to move thru the eastern US. Atmospheric conditions could become less favorable for Ana after its parent upper vortex slides eastward and away by 72 hours...exposing Ana to northerly shear and upper-level convergence occuring on the back flank of the departing upper vortex.

Thermodynamic Outlook for the Forecast Period...Ana is currently over a sub-26 deg C portion of the Gulf stream warmth. Despite water temps just below 26 deg C...Ana is able to fire pockets of showers and t-storms due to de-stabilizing cold air of its parent upper vortex as mentioned in the above current prognosis section. However the thermodynamic environment for Ana does not look that good for the forecast period...with the system soon to drift westward into a cool shelf of waters well below 26 deg C located along the SE US shoreline...and with water vapor satellite animation showing dry air caused by western convergence of its parent upper vortex wrapping in and breaking up the showers and t-storms from time to time.



Track Forecast...The latest computer model runs and my forecast track shown above are all southward adjustments from 24 hours ago...because Ana has been stationary over the last 24 hours while not being able to escape the grip of the north side of its parent upper vortex. My track forecast above is southwest of the NHC's and more in alignment with the 18Z GFS model run as the NHC's short-term forecast track shows a northwest direction while current satellite animation shows that a westward track is instead beginning.

Intensity Forecast...I am below the NHC intensity guidance due to the not so favorable thermodynamic picture painted in the above thermodynamic outlook section...and due to potentially less favorable atmsopheric conditions beginning in 72 hours as noted toward the end of the above atmospheric outlook section. Due to these not so favorable conditions...I am also reluctant to suggest that Ana will make the transition to fully-tropical status.

Impact Forecast...My impact swath in the above forecast graphic is based on extrapolating the 11 PM EDT NHC tropical storm wind field along my forecast track for the portion of the track where Ana is a subtropical storm.

2015 Atlantic Hurricane Season Birdseye Discussion #4

By: NCHurricane2009, 10:59 AM GMT on May 07, 2015

2015 Atlantic Hurricane Season Birdseye Discussion #4

...THURSDAY MAY 7 2015 6:58 AM EDT...
The subtropical disturbance offshore of the southeastern United States has developed into a well-organized subtropical surface low centered just offshore of the Carolinas. Therefore their is a high risk a subtropical or tropical depression or storm could form later today with sea swells...rip currents...and gusty winds affecting the Carolina shore as this system develops. Rain is also possible in the eastern Carolinas beginning later today. See special feature section below for additional details on this developing situation.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z and 0728Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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...SUBTROPICAL LOW INVEST 90-L...
Current prognosis...Within the last 24 hours this disturbance developed a surface circulation that was elongated north-south with two tighter centers...one that was observed just east of Florida and just northwest of the Bahamas...and another located further north closer to the Carolina shore. During the overnight hours the southern circulation lost thunderstorm activity on satellite pictures and the northern circulation has become the dominant and has become well organized within the last couple of hours. Therefore this system is currently centered at 31N-77.5W...in other words is 3.3 degrees latitude further north than I forecated yesterday. Therefore I have shifted my forecast below further north from the previous which means the eastern Carolinas will see effects from this storm sooner than previously anticipated...with the system's outer clouds already overspreading the Carolinas on satellite pictures with heavier weather possibly rotating in as early as later today. It is possible tropical storm watches or warnings could be hoisted on the Carolina shore at any time today should this system be upgraded by the National Hurricane Center.

Atmospheric Outlook for the Forecast Period...At the surface the Atlantic is dominated by 1026 mb ridge. Thru the forecast period...this ridge will continue to dominate while supported by western convergence of the shortwave upper trough currently offshore of Canada (marked by blue-dashed line in top-center of the above atmoshperic features chart). At the upper-levels...latent heat release of this disturbance's showers and thunderstorms has amplified upper ridging east of the disturbance's cut-off upper trough...which is causing the upper trough to amplify into a cut-off upper vortex to the southwest. The GFDL and GFS models now suggest the system moving northward initially on the west side of aforemetioned 1026 mb Atlantic ridge...followed by a counter-clock loop about the north side of the upper vortex as the upper vortex slides eastward and away such that this system is sliding southwest along or just offshore of the South Carolina coast by the end of the forecast. On the other hand the latest CMC suggests this system will be far north enough to escape the influence of the upper vortex such that the track is pre-dominantly northward along the west side of the 1026 mb Atlantic ridge. I am not fully buying into the counter-clock loop solution shown by GFS and GFDL as the GFS and GFDL 0000Z positions were too far south of where the system was actually located during 0000Z. At the same time I do not want to fully throw out the counter-clock loop solution. So as a compromise between these solutions I show the system stalling at 34N-79W in the 48 to 72 hour timeframe.

Thermodynamic Outlook for the Forecast Period...Disturbance has moved northward such that it is now over the narrow swath of Gulf stream warmth...which is just below 26 deg C because we are still only in early May. However potential for subtropical or tropical development remains as the forecast cut-off upper vortex consists of colder upper air that is already showing signs of de-stabilizing the atmosphere as evidenced by thunderstorm pockets firing over and northwest of the system's surface center. I am keeping the forecast intensity of this system shown below on the conservative side due to the sub-26 deg C Gulf Stream and the fact the circulation center will be entering the cool shelf of waters well below 26 deg C currently located along the SE US coast by 24 to 48 hrs.

24 Hr Forecast (0000Z May 8)...45 mph max sustained wind subtropical storm centered just offshore of and south of Cape Fear North Carolina at 33N-78W.

48 Hr Forecast (0000Z May 9)...35 mph max sustained wind subtropical depression centered just inland over North Carolina/South Carolina border at 34N-79W.

72 Hr Forecast (0000Z May 10)...Remnant low centered just inland over North Carolina/South Carolina border at 34N-79W.

2015 Atlantic Hurricane Season Birdseye Discussion #3

By: NCHurricane2009, 9:17 AM GMT on May 06, 2015

...WEDNESDAY MAY 6 2015 5:20 AM EDT...
Frontal boundary disturbance in the western Atlantic has evolved into a subtropical disturbance consisting of a cut-off upper trough (marked by blue-dashed line in eastern Gulf of Mexico and Caribbean in atmospheric features chart below) and surface trough (marked by red-dashed line over the western Bahamas). Their is a high chance that this system evolves into a subtropical storm to affect the southeastern United States over the next few days...see special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0135Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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...SUBTROPICAL DISTURBANCE...
Current prognosis...As of 0000Z this disturbance consists of a surface trough over the western Bahamas (marked by red-dashed line in the above atmospheric features chart) with widespread cloudiness...showers...and thunderstorms enhanced by upper divergence on the east side of a cut-off upper trough (marked by blue-dashed line over eastern Gulf of Mexico and central Caribbean Sea) covering the southeastern United States coast...eastern Cuba....and the western Bahamas.

Atmospheric Outlook for the Forecast Period...At the surface the western Atlantic is dominated by 1030 mb ridge. Thru the forecast period...this ridge will continue to dominate while supported by western convergence of the shortwave upper trough currently over SE Canada that is also about to move into the Atlantic. The west side of this ridge will keep this disturbance on a slow northward track close to the southeastern United States shore. At the upper-levels...computer models suggest that the latent heat release of showers and thunderstorms will amplify upper ridging to the east of the disturbance's cut-off upper trough...causing the upper trough to amplify into a shear-reducing cut-off upper vortex by 48 hours. Many of the current model runs suggest a westward hook in track into the southeastern United States by 72 and 96 hours due to forecast strengthening of the western Atlantic surface ridge and due to the surface circulation moving around the north side of the parent upper vortex. By 120 hours it is likely this system will dissipate into a remnant low due to land interaction and increasing shear as the overhead upper vortex will shift eastward and away.

Thermodynamic Outlook for the Forecast Period...Disturbance is currently over 26 deg C and above waters supportive of tropical development. As the disturbance moves further north by 24 to 72 hours it will be traversing over a narrow swath of Gulf stream warmth. Although much of the Gulf stream offshore of the SE US has water temps just below 26 deg C (because we are still only in early May)...potential for subtropical or tropical development remains as the forecast cut-off upper vortex consists of colder upper air that will help de-stabilize the atmosphere over waters below 26 deg C. However I am keeping the forecast intensity of this system shown below on the conservative side due to the sub-26 deg C Gulf Stream and the fact the circulation could be exposed to the cool shelf of waters well below 26 deg C currently located along the SE US coast by 96 hrs.

24 Hr Forecast (0000Z May 7)...Surface low centered just north of the western Bahamas at 27.7N-77W with widespread showers/clouds/t-storms occuring in a comma shape north and east of the center.

48 Hr Forecast (0000Z May 8)...Subtropical cyclone formation centered offshore of southeastern United States at 31N-76W.

72 Hr Forecast (0000Z May 9)...45 mph max sustained wind subtropical storm centered offshore of the Carolinas at 32.5N-77.5W.

96 Hr Forecast (0000Z May 10)...45 mph max sustained wind subtropical storm with center making landfall on South Carolina coast at 32.5N-80W.

120 Hr Forecast (0000Z May 11)...Remnant low over eastern Carolinas centered at 34.5N-79.5W

2015 Atlantic Hurricane Season Birdseye Discussion #2

By: NCHurricane2009, 11:42 AM GMT on May 05, 2015

...TUESDAY MAY 5 2015 7:40 AM EDT...
Frontal boundary disturbance consisting of cut-off upper trough (marked by blue-dashed line in eastern Gulf of Mexico and western Caribbean in atmospheric features chart below) and decaying surface front (marked by red-dashed line over the eastern Bahamas) has become better defined in satellite pictures. Computer model runs now show the upper trough amplifying into a shear-reducing upper vortex for a longer period. Coupled with continued computer model support for subtropical or tropical cyclone formation...I have upgraded this system to a special feature on this blog. See special feature section below for additional details on this developing situation.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1924Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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...FRONTAL BOUNDARY DISTURBANCE...
Current prognosis...As of 0000Z this disturbance consists of a tail end of a frontal zone decaying into a surface trough over the eastern Bahamas (marked by red-dashed line in the above atmospheric features chart) with widespread cloudiness...showers...and thunderstorms enhanced by upper divergence on the east side of a cut-off upper trough (marked by blue-dashed line over eastern Gulf of Mexico and Western Caribbean Sea) covering the Cayman Islands...Cuba...the Bahamas...southeast Florida...and southwest Atlantic.

Atmospheric Outlook for the Forecast Period...At the surface a 1028 mb ridge has moved offshore from North America and into the western Atlantic. Thru the forecast period...this ridge will dominate the western Atlantic while supported by western convergence of the shortwave upper trough currently over the NE US/SE Canada that is also about to move into the Atlantic. The west side of this ridge will keep this disturbance on a slow northward track close to the southeastern United States shore thru the forecast period. At the upper-levels...computer models suggest that the latent heat release of showers and thunderstorms will amplify upper ridging to the east of the disturbance's cut-off upper trough...causing the upper trough to amplify into a shear-reducing cut-off upper vortex by 72 hours. Many of the current model runs suggest a westward hook in track toward the southeastern United States coast by 96 and 120 hours due to forecast strengthening of the western Atlantic surface ridge and due to the surface circulation moving around the north side of the parent upper vortex.

Thermodynamic Outlook for the Forecast Period...Disturbance is currently over 26 deg C and above waters supportive of tropical development. As the disturbance moves further north by 48 to 96 hours it will be traversing over a narrow swath of Gulf stream warmth. Although much of the Gulf stream offshore of the SE US has water temps just below 26 deg C (because we are still only in early May)...potential for subtropical or tropical development remains as the forecast cut-off upper vortex consists of colder upper air that will help de-stabilize the atmosphere over waters below 26 deg C. However I am keeping the forecast intensity of this system shown below on the conservative side due to the sub-26 deg C Gulf Stream and the fact the circulation could be exposed to the cool shelf of waters well below 26 deg C currently located along the SE US coast by 120 hrs.

24 Hr Forecast (0000Z May 6)...Surface trough over the western Bahamas with widespread showers/clouds/t-storms over Cuba...Bahamas...and SW Atlantic.

48 Hr Forecast (0000Z May 7)...Surface low centered just north of the western Bahamas at 27.7N-77W with widespread showers/clouds/t-storms occuring in the eastern half of the circulation.

72 Hr Forecast (0000Z May 8)...Subtropical cyclone formation centered offshore of southeastern United States at 31N-76W.

96 Hr Forecast (0000Z May 9)...45 mph max sustained wind subtropical storm centered offshore of the Carolinas at 32.5N-77W.

120 Hr Forecast (0000Z May 10)...45 mph max sustained wind subtropical storm moving toward Carolina coast centered at 32.5N-79W.

2015 Atlantic Hurricane Season Birdseye Discussion #1

By: NCHurricane2009, 5:22 AM GMT on May 04, 2015

...MONDAY MAY 4 2015 1:22 AM EDT...
Resuming my daily birdseye view discussions on the Atlantic tropics even though Atlantic hurricane season starts June 1...due to the following potential for tropical development offshore of the southeastern United States...

A surface frontal zone and associated upper trough has moved offshore from eastern North America and into the western Atlantic...with focus shifting to a southern fracture of the upper trough (marked as a blue dashed line over the eastern Gulf of Mexico and western Caribbean in the atmospheric features chart below) and the tail end of the surface frontal zone (marked as a solid red line over the Cayman Islands...eastern Cuba...and eastern Bahamas). Divergence on the east side of the upper trough is supporting an enhanced area of showers and thunderstorms over the tail end of the frontal zone...with computer models agreeing that this disturbance will evolve into a surface low that drifts northward into the waters offshore of the southeastern United States while steered on the west side of the 1024 mb ridge currently moving into the western Atlantic. A special pre-season National Hurricane Center 5-day tropical weather outlook suggests a 30% chance of tropical or subtropical cyclone formation from this system. Upper wind forecasts do not show the upper trough amplifying into a shear-reducing cut-off upper vortex except for a breif period 5 days from now. Since this is only a short window of forecast favorable upper winds in a timeframe that is a bit distant for forecast skill...I am currently not confident enough to consider this sytem a special feature on this blog.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0127Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

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...

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).


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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