2012 Atlantic Hurricane Season Birdseye Discussion #17

By: NCHurricane2009 , 5:20 AM GMT on May 26, 2012

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...MAY 26 2012...1:21 AM EDT...
Subtropical Storm Beryl forms south of Cape Hatteras, NC and east of Charleston, SC! I think we will need to take a look back at records to see if there ever was an Atlantic season with two named cyclones before June 1. Residents from the Carolinas to NE Florida should keep tabs on this developing situation. See special features section below for further details.

This is the seventeenth birdseye discussion of the 2012 Atlantic Hurricane Season. See previous discussion #3 concerning the idea behind this new type of discussion forum.

Any feedback on how to improve these discussions can be left in the comments section below. In particular...any suggestions on how to improve the standard two "birsdeye view" charts below will be much appreciated. Are you able to understand the markings in the charts? Are you able to relate what is said in the discussions to these charts?

One improvement being attempted this evening is the implementation of paragraph (P) numbers in general discussions. Paragraphs will cross-reference each other to make the discussion easier during complex weather patterns.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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 BERYL...
Some of my predictions (from discussion #16) that came true this late evening on Invest 94-L were:
(a) Upper voriticty to the SW amplified...which hooked the track more northward...reduced the shear....and divergence on the NE side of this upper voriticty and adjacent upper ridging strengthened 94-L to Subtropical Storm Beryl right on cue.
(b) The northward track has slowed due to a blocking pattern consisting of what is now surface ridging in the Gulf of Mexico (mentioned in paragraph P6 below)...and what is now a 1033 mb ridge just south of Newfoundland (mentioned in paragraph P1).

The rest of the predictions I made in discussion #16 fell apart...mainly track-wise. Beryl is much further northeast in position than I thought it would be...but this is because I made a forecast track on a center that had not yet become established.

But the bigger flaw in discussion #16's forecast was expecting a frontal system from the NW (now covered in paragraph P1 below) to break through the aforementioned blocking pattern and drag the system in an offshore clockwise loop turn thru 0000Z May 28. I should have listened more to the models...which were correctly playing down the steering influence of this frontal system. However...I think there is some very light steering influence this evening from this frontal system...as the recent infrared imagery still shows a northward track for Beryl in Figure 1 below. Utlimately...1016 mb ridge behind this front and over Iowa (paragraph P1) will re-enforce the blocking pattern to the northwest of Beryl...forcing Beryl to turn west and then southwest while steered by the block.

I have adjusted my predicted track from the NHC's as shown in Figure 2 below...accounting for the initial northward motion announced in the first NHC public advisory and supported by the two satellite frames in Figure 1. Intensity-wise...the most recent AVN-color-scheme infrared satellite shows a decrease in the orange-shaded deep T-storm clouds...all as Beryl ingests dry air from the Gulf of Mexico. Source of this dry air covered in paragraph P6. I expect Beryl will pulse on and off in central T-storm activity as it slowly mixes out the dry air with vertical motion...the vertical motion supported by instability driven between the warm ocean surface and cold upper vorticity. Therefore...I don't expect full vertical warm core formation (with anticyclonic upper outflow for strengthening) until Sunday (in other words I don't expect a fully tropical Beryl till Sunday). I expect Beryl to then begin weakening as it approaches the Georgia coast (from the shelf of cooler waters W of Gulf stream). Weakening is then exacerbated by westerly vertical shear induced by the frontal system in paragraph P2...the same frontal system that will recurve and accelerate Beryl NE from Georgia thru the Carolina coast late in the forecast period. Land interaction late in the forecast also would contribute to weakening.

The impact forecast in Figure 2 is based on if Beryl follows my track and intensity forecast. Notice that the drawn-in (blue-dashed line) heavy-impact swath has a rightward bias in relation to my forecast track late in the period...an effect I expect from westerly vertical shear forecast by that time.


Figure 1: Latest infrared satellite imagery trend of Subtropical Storm Beryl


Figure 2: My current best-guess forecast for Subtropical Storm Beryl. I don't expect a fully tropical Beryl till Sunday.

...MID-LATITUDES DISCUSSION...
P1...Main energy of frontal system from central US is moving NE into Canada tonight. Lowest surface pressure of frontal system is marked by a 989 mb cyclone approaching the south tip of Hudson Bay. Upper trough of frontal system is just west of this cyclone while supporting the cyclone with upper divergence. Upper convergence west of this upper trough supports a surface ridge to the SW...with a 1016 mb center over Iowa. Warm air advection ahead of this frontal system supports an upper ridge that has sprouted NE across the eastern US from the Texas/Arkansas area. The NE US upper anticyclone ahead of this frontal system has moved into Atlantic Canada and NW Atlantic as an upper ridge wave. Upper convergence E of this upper ridge wave supports a surface ridge center S of Newfoundland which has strengthend from 1028 to 1033 mb in the last 24 hrs...and another ridge center of 1026 mb just NE of Bermuda.

P2...Tail end of frontal system in paragraph P1 features a rapidly developing 989 mb cyclone over W Utah. Upper-level pressures over the west US are falling as this 989 mb cyclone advects in cold air from the NW such that an upper trough is forming. This 989 mb cyclone and attendant upper trough will be the next frontal system hot on the heels of the system in paragraph P1...and is expected to eventually recurve Subtropical Storm Beryl currently off of the US east coast. See special features section for details on this.

P3...Frontal system currently over the high seas S of Greenland has become cut-off from the mid-latitude westerlies...thanks to the Atlantic Canada/NW Atlantic upper ridge wave covered at the end of paragraph P1. In the upper-levels...the cut-off is well defined with a small upper vortex. The associated 1000 mb frontal surface cyclone is in the process of whirling cyclonically beneath this new cut-off upper vortex.

P4...Upper ridge axis in north-central Atlantic 24 hrs ago...supported by warm air advection ahead of frontal system in paragraph P3...is now a full-fledged upper anticyclone near the British Isles (based on animation of latest infrared imagery). Eastern upper convergence of this system used to support surface Atlantic subtropical ridging 24 hrs ago...which are now 1026 and 1028 mb centers in the above charts. With these surface ridge centers no longer beneath upper convergence...expect these centers to lose dominance while the 1033 and 1026 mb centers become the dominant.

P5...Massive upper trough in the E Atlantic has become strongly cut-off to the south of British Isles upper anticyclone featured in paragraph P4. In addition...this massive upper trough has split...now an upper vortex NE of the Azores...and a southern upper trough in the mid-ocean. 24 hrs ago...this massive upper trough supported a 1011 mb depression in Spain and surface trough NE of the Azores. Based on 1200Z TAFB and visible satellite animation before sunset...these surface features have evolved into a new frontal extratropical (non-tropical) cyclone NW of Spain in the above charts. Expect this new extratropical cyclone to cyclonically orbit about the upper vortex NE of the Azores. Expect the southern mid-ocean upper trough to merge with the upper vortex mentioned in paragraph P3.

...TROPICAL BELT DISCUSSION...
P6...Upper vorticity remains trapped over the SE US and E Gulf of Mexico ...and has triggering Tropical Storm Beryl tonight as explained in the special features section. Upper convergence west of this vorticity continues to support the long-lived dry air across the Gulf of Mexico...as well as relatively new Gulf of Mexico surface ridging which now connects NE all the way to the 1033 mb center in paragraph P1.

P7...Long-lived Caribbean upper ridging has split into two areas tonight...with an inverted upper trough forming between the split and south of Jamaica. The eastern split is a full-fledged upper anticyclone over the Dominican Republic tonight...supported by warm air advection ahead of subtropical cyclone covered in the special feature section. The western split is a leftover upper ridge axis over SE Mexico and Guatemala. Residual (but strong) dry air dominates the SE half of the Caribbean and tropical waters E of the Lesser Antilles....once created by convergence on the SE side of this Caribbean upper ridging.

P8...A pair of tropical waves are in the tropical belt of the Atlantic...one that has entered the Caribbean from the Lesser Antilles...the other following behind hundreds of miles to the east. Both waves are suppressed by dry air mentioned at the end of paragraph P7 above. Upper easterlies (aligned with low-level easterlies) on the south side of paragraph P7's upper ridging means favorable low shear. If the western of the two tropical waves overcomes the dry air and starts to develop T-storm activity in this low shear environment...this may lead to yet another area of interest. Absolutely no signs of that at this time.

P9...Upper ridge over the E tropical Atlantic is subsiding as a major mid-ocean upper trough is taking shape to the NW of it. This mid-ocean upper trough will be a merger between two current upper features as explained by the last sentence of paragraph P3.

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