2012 Atlantic Hurricane Season Birdseye Discussion #18

By: NCHurricane2009 , 7:42 PM GMT on May 27, 2012

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...MAY 27 2012...3:42 PM EDT...
Beryl is now fully-tropical...is stronger...and its center is heading toward NE Florida. Weather conditions will deteriorate through the rest of this afternoon and evening in SE Georgia and NE Florida. See Special features section for further details.

This is the eighteenth 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?

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0729Z-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...TROPICAL STORM BERYL...
My track forecast positions in the previous discussion were too far NE of the NHC...computer models...and what has actually happened. Therefore...my updated track forecast (in Figure 1 below) more closely follows the NHC track this time around. The NHC track would make the center move ashore at Jacksonville, FL (30N latitude)...all while radar imagery suggests a center currently just south of 30N and visible imagery suggwsts a center just north of 30N. With the radar versus satellite conflicting a bit like this...I will agree with the NHC track (landfall at Jacksonville, FL)....which is down the middle of the sat/radar conflict. Concerning the recurvature to the NE later in the forecast period...I have been following how the frontal system (in paragraph P1) has been ejecting eastward with the HPC surface maps:

(a) I concluded an 18-hourly motion about the width of Colorado.
(b) That suggests the front in E Kansas 18 hours from now (5 AM Mon)
(c) That suggests the front in E Missouri/W Tennessee 36 hours from now (11 PM Mon)...where it can just start to bend Beryl northward as it erodes the blocking ridge (1019 and 1022 mb centers of paragraph P2) to Beryl's north
(d) That suggests the front over the eastern US 54 hours from now (5 PM Tue)...sending Beryl northeastward by that time.

The 8 PM Mon NHC position suggests a NW track by the time the front is in aforementioned position (c). But I think given the current strength of the blocking ridge to Beryl's north...I think a more WNW track is appropriate by that time...so my NE recurving track of Beryl is a bit left of the NHC's as shown in Figure 1 below.

Intensity-wise...the forecast in my previous discussion was much better than my track forecast. As if right on cue with my previous forecast...Beryl gained fully tropical status today (on Sunday) and strengthened to 65 mph winds. The ominous thing however is Beryl has gained 65 mph winds ahead of when my previous forecast said it would. Beryl's cloudiness was best described as a doughnut in the last several hours (as can be typical with a subtropical cyclone beneath a cold core upper low)...featuring a large-radius of clear skies at the center surrounded by a ring of convective T-storm clouds. This ring of T-storms has been intensifying...gaining some warm core anticyclonic outflow at its top (hence why Beryl is now fully tropical)...and finally has contracted such that the large-radius of clear skies is a smaller radius (i.e. now looks more like a hurricane's eye). Therefore...there is a remote chance of a minimal hurricane before landfall tonight..but my newest forecast in Figure 1 is more conservative at 70 mph max central winds (just under hurricane status).

After landfall...my intensity forecast weakens Beryl to a 35 mph wind tropical depression by 11 PM Monday...and then a remnant low by 11 AM Tuesday with 30 mph winds. The NHC and computer models insist that Beryl will then take advantage of upper trough divergence associated with the frontal system recurving her NE...so my max wind speed forecast suggests some re-strengthening after 11 AM Tuesday. But the status of Beryl will be questionable by that point...because it is more likely to be non-tropical (extratropical) as it re-strengthens...as such a re-strengthening method is a non-tropical method.

Finally...all impacts expected are summarized in Figure 1. Tonight...the most severe impacts are likely to be in the Jacksonville metro area in NE Florida with damaging winds and heavy rain. In fact...winds have been rising hour-by-hour in advance of the storm center in Jacksonville...based on official NWS (National Weather Service) station reports. The blue-dashed swath of impacts in Figure 1 is first symmetrical about the center using the current wind radii from the NHC 11 AM advisory. I then shrink the swath diameter thru landfall and weakening. Notice by 11 AM Tue...the swath has a rightward bias with respect to forecast central position...the rightward bias caused by westerly vertical shear associated with the incoming frontal upper trough. This rightward biased structure is expected from 11 AM Tue and onwards...but with a NE track at that time as well...the swath ends up being symmetrical about my forecast track.


Figure 1: My current best-guess forecast for Tropical Storm Beryl.

...MID-LATITUDES DISCUSSION...
P1...In the past 36 hours...frontal system over the western US has been largely stationary but is beginning to eject eastward. It had a surface 989 mb center in W Utah 36 hrs ago that is now 996 mb over W Nebraska. The timing of how fast this frontal system and its supporting upper trough moves east is crucial...as this will affect when exactly Tropical Storm Beryl recurves to the NE (see special feature section for details).

P2...Upper ridge was over the eastern US 36 hrs ago...once supported by warm air advection ahead of the frontal system in paragraph P3 below...is now supported by warm air advection ahead of the system in paragraph P1 and has shifted westward into the central US where the warm air advection is maximal. Eastern convergence of this upper ridge supports surface ridge centers of 1019 mb in E Tennesee and 1022 mb E of North Carolina.

P3...A frontal system was rapidly ejected NE from the central US into SE Canada 36 hrs ago...and now this front is ejecting eastward into the Atlantic high seas W of Greenland. Lowest surface pressure of this frontal system is 988 mb and about to make landfall in SW Greenland. Convergence on the west side of this front's upper trough supports a surface 1029 mb center over S Hudson Bay. The southern end of this upper trough appears to be fracturing southeastward (due to the strength of the upper ridge mentioned in paragraph P2)...with divergence east of this fracture supporting SE-moving cloudiness E of Bermuda that shows some light cyclonic turning in satellite animations.

P4...In the upper-levels...an upper vortex S of Greenland 36 hrs ago was expected to merge with a southern mid-ocean upper trough (see last sentence of discussion #17 paragraph P5). After this merger took place...this large mid-ocean upper trough is splitting...with the upper vortex S of Greenland now located NW of the Azores and another upper vortex located far NE of the Lesser Antilles. The northern upper vortex was supporting a 1000 mb frontal cyclone...which has since whirled beneath the upper vortex such that a 1012 mb deep-layered low is NW of the Azores as marked in the above charts.

P5...Full-fledged upper anticyclone near the British Isles has shifted west while now being associated with warm air advection ahead of frontal system in paragraph P3. When this upper anticyclone was just merely an upper ridge axis day ago...its eastern convergence supported Atlantic surface subtropical ridging that has since weakened since the surface ridge had split from this upper convergence. Currently this weaker surface ridge consists of 1024 and 1022 mb centers N of the Canary Islands while located SE of the 1012 mb deep-layered cyclone in paragraph P4.

P6...Thirty-six hours ago...an upper vortex NE of the Azores created a new frontal extratropical (non-tropical) cyclone NW of Spain while cut-off to the south of the upper anticyclone in paragraph P5. This new extratropical cyclone has since cyclonically orbited to a position beneath the upper vortex...and we now have a deep-layered non-tropical low spinning on satellite to the SW of the British Isles as marked in the upper-right corner of the above charts.

...TROPICAL BELT DISCUSSION...
P7...Upper vorticity remains trapped offshore of SE US and E Gulf of Mexico...and is located very near Tropical Storm Beryl. Upper convergence west of this vorticity and east of the upper ridge in paragraph P2 supports the long-lived sinking dry air across the Gulf of Mexico.

P8...Long-lived Caribbean upper ridging remains split...with a central Caribbean upper trough between the split that has merged with the upper vorticity very near Tropical Storm Beryl. The eastern split is a full-fledged upper anticyclone SE of the Dominican Republic...supported by warm air advection ahead of the deep-layered cyclone that is Tropical Storm Beryl. The western split is a leftover upper ridge axis over SE Mexico and Guatemala. Residual dry air dominates E 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. This residual dry air has been kicked out of the western Caribbean...replaced by moistening air created by upper divergence E of the central Caribbean upper trough and W of the upper anticyclone SE of the Dominican Republic.

P9...Pair of tropical waves has changed in the last 36 hours. The western of the two had entered the Caribbean Sea...and was in a favorable low shear environment on the south side of the Caribbean upper ridging in paragraph P8...but suppressed by the residual dry air also mentioned in paragraph P8. This western tropical wave has been removed from 0600Z TAFB as if it dissipated...but I kept it in my charts above based on the 0600Z TAFB isobars. Even if this western tropical wave still exists...it is entering an unfavorable southwesterly vertical shear environment caused by central Caribbean upper trough also mentioned in paragraph P8. Meanwhile...the eastern of the two tropical waves has been kept stationary (midway between Cape Verde Islands and Lesser Antilles) in the last three days of TAFB analyses...as if its transitioning to a surface trough supported by divergence SE of an upper vortex. This upper vortex is located well NE of the Lesser Antilles (paragraph P4).

P10...Upper ridge over the E tropical Atlantic continues...and the air in the eastern half of the tropical Atlantic has seen a great increase in moisture content thanks to divergence beneath this upper ridge and divergence east of the mid-oceanic upper trough (now two upper vortices) in paragraph P4.

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1. KoritheMan
7:47 AM GMT on May 28, 2012
I don't know why these don't garner more comments. They're spectacular.
Member Since: March 7, 2007 Posts: 601 Comments: 21199

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