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2012 Atlantic Hurricane Season Birdseye Discussion #143
By: NCHurricane2009 , 12:29 PM GMT on October 26, 2012
...FRIDAY OCTOBER 26 2012...8:30 AM EDT...
As weather conditions gradually improve in the Bahamas...Hurricane Sandy making a westward jab in track closer to the United States east coast...and as a result it is now clear that Sandy will be bringing its wrath toward the mid-Atlantic and parts of the northeast United States as an intensifying non-tropical gale by early next work week. See the Sandy special feature section below for additional details on this potentially historic storm.
Tony continues east-northeast across the open Atlantic...and has completed transition into a non-tropical surface low during the last 24 hrs. See paragraph P2 for statement on remnant of Tony.
Tropical wave activity west-southwest of the Cape Verde Islands...associated with a pair of tropical waves in paragraph P4 of the tropical belt discussion...continues struggling under less favorable upper winds.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1933Z-released HPC 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...
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...HURRICANE SANDY...
Concerning the east coast of the United States...offshore western Atlantic waters...and interior sections of the mid-Atlantic and parts of the northeastern United States located inside the blue-dashed impact swath of Figure 1...impact statments (a) through (c) are fairly descriptive of what is likely ahead. Please take these hazards seriously and listen to local officials and media. Latest coastal watches and warnings are found under the public advisory for Sandy at www.nhc.noaa.gov. Latest local forecast statements...for the coast and inland areas...for those likely to be affected by Sandy are found at www.nws.noaa.gov.
Track-wise for Sandy...she has hooked more leftward than I previously anticipated. In fact...I previously had not anticipated the leftward hook at all. It appears over the last couple of days...a vast region of split flow upper divergence between Sandy's warm core upper anticyclone and an upper vortex near west Cuba significantly expanded the size of the hurricane's cloud field...particularly north and east of the center. In turn...the latent heat release of this gigantic cloud field has recently amplified the warm core upper anticyclone against the upper vortex...causing the definition of the upper vortex to be more amplified. Sandy's leftward (westward) hook is the result of her getting steered by the NE quad of the amplified upper vortex in conjunction with the south side of the E North America surface ridge mentioned in paragraph P2. When comparing the 00Z GFS initialization with the above atmo chart...it is clear the GFS has underplayed the amplitude of the upper vortex and placed it too far west...so in response I have my forecast track left of the 00Z GFS and left of the NHC track. After 11 PM tonight...Sandy should still turn more NE and offshore because the models create a strong North America surface ridge on the convergent back side of the paragraph P1 upper trough...and such a ridge would block a continued NW track into the SE US. It is interesting to note the 00Z GFS by 11 PM Saturday has Sandy going straight east for a brief period...but I think it now overdoes the attraction to the paragraph P2 cyclone because I am now to the left of the GFS. Therefore...I do not expect a brief period of a straight eastward track.
It is clear the non-tropical version of Sandy will not continue NE out to sea. Instead...she will hooks leftward toward the NE and mid-Atlantic US. Her westward adjustment in track means that she will be hugged by a fragment of the North America surface ridge to the north...and that she will interact with the paragraph P1 upper trough. She will take maximum advantage of the eastern divergence of the incoming paragraph P1 upper trough and intensify non-tropically. Cool air advection on her back side in turn will amplify the upper trough into an upper vortex that would whirl her NW. The closer Sandy is to the US shore...the stronger the cool air advection...and the faster the amplification into an upper vortex such that the radius of the NW curving track is tighter. That is why my forecast track has a tighter radius than the more offshore GFS and NHC solutions.
Intensity-wise for Sandy...she has weakened from a category 2 to 1 hurricane in the last 24 hrs as the aforementioned mass area of split flow upper divergence has broadened her low pressure field. This broadening has made her pressure gradient more lax...and that is why her winds have died down. But despite the max winds dying down...her tropical storm wind radius has gone up due to the expansion of the low pressure field size. Her satellite apperance does not resemble a hurricane...so I expect her to soon be downgraded to a strong tropical storm of 70 mph max winds. She could even be downgraded to a subtropical storm due to her interaction with the upper vortex near the west tip of Cuba. I still insist on transition to non-tropical by 11 PM Sunday...then possible re-intensification of Sandy as a non-tropical gale of 75 mph (minimal hurricane) max winds for her mid-Atlantic/NE US landfall on Monday. That is why their is mention of coastal and inland wind damage toward the storm center in impact statement (c) of Figure 1. She will then whirl beneath the less-divergent axis of the amplifying paragraph P1 upper trough...causing her to weaken as a post-mature non-tropical gale as she moves inland. That is why impact statement (c) says she will weaken as she moves inland.
Figure 1: Hurricane Sandy Forecast
My impact swath initialization in Figure 1 is based on extrapolating the 5 AM tropical storm wind radius along my forecast track. Notice that late in the forecast...I expand the wind (impact swath) radius only in the NE half of the storm as she intensifies non-tropically. This is because as Sandy becomes non-tropical...her SW half will whirl in dry and cold air beneath the upper trough axis...while her NE half stays very moist. It is the rain bands in the NE half that will then mix down the strong upper-level winds of the paragraph P1 upper trough's jet stream to the surface.
P1...Surface frontal system in the mid-latitudes is now advancing eastward into central North America this morning. In the upper-levels...the system continues to be anchored by a large upper trough from the western US whose western convergence supports a 1027 mb ridge. Vast divergence east of this upper trough continues driving a few frontal depressions across the central US. Low-level warm air advection ahead of the frontal depressions supports an upper ridge that has moved from the central to the eastern US.
P2...Deep-layered low pressure system/upper trough centered over SE Canada has finally fully shifted into the western Atlantic. In the last 24 hrs...the original surface center of this of this system has phased out offshore of the Canadian east coast...while the newer less-than-1004 mb center offshore of Newfoundland in the previous discussion has intensified to less-than-992 mb while supported by the eastern divergence of the upper trough. This same eastern divergence in the last 24 hrs has transitioned Tropical Storm Tony into a non-tropical low as it tracks ENE. Cool air advection behind the intensifying less-than-992 mb surface low pressure has caused the upper trough to amplify into an upper vortex stacked above the surface low. Meanwhile...1026 to 1027 mb surface ridge over eastern North America remains supported by western upper convergence of the upper trough. Warm air advection ahead of the aforementioned less-than-992 mb cyclone is maintaining the full-fledged NE Atlantic upper anticyclone.
P3...Upper trough in the NE Atlantic remains stalled offshore of Spain and Portugal to the SE of the upper anticyclone mentioned in paragraph P2 above. Upper convergence on the west side of the upper trough supports 1018 mb surface ridge in the eastern Atlantic. 996 mb gale in the previous discussion has moved eastward and weakened to about 1000 mb while passing below the non-divergent upper trough axis...and its east side has absorbed the remnant low of Rafael.
...TROPICAL BELT DISCUSSION...
P4...Upper ridge in the eastern tropical Atlantic persists. Pair of tropical waves WSW of the Cape Verde Islands continue to produce enhanced showers and t-storms under the favorable upper outflow of the upper ridge...and the western of the two tropical waves has spun up a 1008 mb surface low that was briefly organized yesterday afternoon and early evening. However...this activity has since become less organized this early morning as the tropical waves continue to struggle in southerly vertical shear on the west side of the upper ridge.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.