Tropical Storm ALEX

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TROPICAL STORM ALEX DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012010
400 AM CDT MON JUN 28 2010
 
DEEP CONVECTION WITH CLOUD TOPS OF -80C TO -84C HAVE DEVELOPED NEAR
AND AROUND THE CENTER OF ALEX DURING THE PAST FEW HOURS. AN AIR
FORCE RESERVE UNIT AIRCRAFT AROUND 05Z FOUND THE CENTRAL PRESSURE
TO STILL BE AROUND 991 MB...BUT FLIGHT-LEVEL WINDS HAD INCREASED TO
51 KT...EQUAL TO ABOUT 38 AT THE SURFACE. THE AIRCRAFT ALSO
MEASURED AN SFMR SURFACE WIND OF 41 KT IN THE NORTHERN QUADRANT ON
ITS OUTBOUND LEG. BASED ON THIS INFORMATION AND THE MARKED INCREASE
IN CENTRAL DEEP CONVECTION SINCE THE RECON FIX...THE INITIAL
INTENSITY IS SET AT 45 KT.
 
THE INITIAL MOTION ESTIMATE IS 315/05 BASED ON RECON FIX DATA.
COMPARED TO LAST NIGHT...THE MODELS ARE IN MUCH BETTER AGREEMENT ON
THE EVOLUTION OF THE SYNOPTIC-SCALE FLOW PATTERN ACROSS THE U.S.
AND THE GULF OF MEXICO. IN FACT...THE 500 MB HEIGHT AND WIND FIELDS
ARE NEARLY IDENTICAL WITH THE STRENGTH AND PLACEMENT OF THE
DEVELOPING TROUGH-RIDGE PATTERN THROUGH 72 HOURS. DESPITE THESE
STRIKING SIMILARITIES...HOWEVER...THERE IS STILL CONSIDERABLE
DIVERGENCE IN THE FORECAST TRACKS...ESPECIALLY AFTER 48 HOURS. FOR
THE NEXT 2 DAYS OR SO...THE MODELS ARE IN GENERAL AGREEMENT ON A
SLOW NORTHWESTWARD MOTION. AFTER THAT...THE GFS...GFS-PARALLEL...
CMC...HWRF...AND GFDL MODEL KEEP ALEX ON A NORTHWESTWARD TRACK AND
BRING THE CYCLONE INLAND ALONG THE LOWER OR CENTRAL TEXAS COAST. IN
CONTRAST...THE ECMWF...UKMET...AND NOGAPS MODELS TAKE ALEX WESTWARD
INTO THE NORTHEASTERN COAST OF MEXICO...WITH THE ECMWF HAVING THE
MOST SOUTHERN TRACK OF THOSE MODELS. HOWEVER...THE ENTIRE NHC MODEL
SUITE HAS SHIFTED NORTH AGAIN...ALONG WITH THE ECMWF MODEL. THE
ONLY DIFFERENCE I CAN SEE BETWEEN THE MODELS IS THAT THE THE
ECMWF...UKMET...AND ESPECIALLY NOGAPS DEPICT ALEX AS A SMALLER AND
WEAKER CYCLONE THAN THE OTHER MODELS ARE FORECASTING. GIVEN THAT
ALEX IS EXPECTED TO BE A RELATIVELY LARGE HURRICANE BY 72 HOURS...
GREATER WEIGHT WAS PLACED ON THE OTHER MODEL SOLUTIONS... WHICH HAS
RESULTED IN A NORTHWARD SHIFT OF THE FORECAST TRACK...BUT STILL
REMAINS SOUTH OF THE NHC CONSENSUS MODEL..TVCN.

THE NORMALLY ROBUST GFDL AND HWRF MODELS ARE STILL ONLY FORECASTING
MODEST INTENSIFICATION OF ALEX...WHICH REMAINS SOMEWHAT PERPLEXING
GIVEN THE VERY LOW VERTICAL SHEAR ENVIRONMENT AND IMPRESSIVE
OUTFLOW ENVIRONMENT IN WHICH ALEX IS CURRENTLY IN AND IS FORECAST
TO REMAIN EMBEDDED IN FOR THE NEXT SEVERAL DAYS. THE CURRENT
CENTRAL PRESSURE IS MORE TYPICAL OF SYSTEM NEARING HURRICANE
STRENGTH. GIVEN THAT THE SHEAR IS EXPECTED TO REMAIN QUITE LOW AND
THE ATMOSPHERE IS FORECAST TO REMAIN VERY MOIST IN THE MID-LEVELS
...I SEE NO REASON WHY ALEX SHOULD NOT CONTINUE TO STRENGTHEN...AND
POSSIBLY EVEN BECOME A MAJOR HURRICANE BEFORE LANDFALL. THE
OFFICIAL INTENSITY FORECAST IS SLIGHTLY HIGHER THAN THE VERY
RELIABLE LGEM MODEL...WHICH BRINGS ALEX UP TO 90 KT BY 72 HOURS.


FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/0900Z 19.7N  91.6W    45 KT
 12HR VT     28/1800Z 20.3N  91.9W    55 KT
 24HR VT     29/0600Z 21.4N  92.7W    65 KT
 36HR VT     29/1800Z 22.4N  93.6W    75 KT
 48HR VT     30/0600Z 23.3N  94.7W    85 KT
 72HR VT     01/0600Z 24.6N  97.0W    95 KT
 96HR VT     02/0600Z 25.6N  99.2W    40 KT...INLAND
120HR VT     03/0600Z 26.5N 101.0W    20 KT...DISSIPATING INLAND
 
$$
FORECASTER STEWART
 
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