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Tropical Storm ARLENE


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TROPICAL STORM ARLENE DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU JUN 09 2005
 
SATELLITE IMAGERY AND RECON DATA INDICATE THAT ARLENE HAS CHANGED
LITTLE OVER THE PAST 6 HOURS. RECON REPORTED 1500 FT WIND OF 46 KT
IN THE NORTHEAST QUADRANT AROUND 2115Z...BUT A SUBSEQUENT PASS
THROUGH THE SAME AREA REVEALED ONLY 32 KT WINDS. SINCE THE
CONVECTION HAS WEAKENED SOME AND BECOME A LITTLE RAGGED...THE
INTENSITY IS BEING MAINTAINED AT 35 KT. HI-RES VISIBLE SATELLITE
IMAGERY AND RECON DATA INDICATE MULTIPLE SMALL CIRCULATIONS HAVE
BEEN ROTATING AROUND INSIDE A LARGER WELL-DEFINED OUTER CYCLONIC
ENVELOPE. THE INITIAL POSITION IS AN AVERAGE OF THESE VORTEX
POSITIONS AND VERY CLOSE TO A 09/2324Z QUIKSCAT CENTER POSITION.

THE INITIAL MOTION ESTIMATE IS 350/07. THE AFOREMENTIONED QUIKSCAT
POSITION WOULD SUGGEST THAT ARLENE MAY BE A LITTLE FARTHER WEST...
BUT I HAVE OPTED TO STAY CLOSER TO WHAT DEEP CONVECTION EXISTS AND
WITHIN THE RECON VORTEX ENVELOPE. NHC MODEL GUIDANCE REMAINS IN
STRONG AGREEMENT ON ARLENE MOVING ACROSS WESTERN CUBA TONIGHT AND
THEN TURNING NORTH-NORTHWESTWARD OVER THE SOUTHEASTERN GULF OF
MEXICO ON FRIDAY. THIS ANTICIPATED TURN IS IN RESPONSE TO THE
CYCLONE BEGINNING TO FEEL THE INFLUENCE OF A BUILDING RIDGE ACROSS
THE WESTERN ATLANTIC...SOUTHEASTERN U.S....AND THE FLORIDA
PENINSULA. ONE CONCERN IS THE UPPER-LEVEL OUTFLOW IN THE EASTERN
SEMICIRCLE IS FORECAST TO GET PINCHED BETWEEN DIGGING TROUGHS OVER
THE WESTERN GULF AND ALSO OVER THE CENTRAL ATLANTIC. THIS TYPE OF
BLOCKING PATTERN OFTENTIMES RESULTS IN THE LOW- TO MID-LEVEL RIDGE
BEING STRONGER...WHICH WOULD HELP TO NUDGE ARLENE A LITTLE MORE
WESTWARD. THE OFFICIAL FORECAST IS JUST AN EXTENSION OF THE
PREVIOUS FORECAST TRACK.
 
MID-LEVEL DRY AIR NOTED IN WATER VAPOR IMAGERY AND NOAA G-IV JET
AIRCRAFT DATA HAS BEEN PUNCHING INTO THE CENTER FROM THE SOUTHWEST
AND HAS TEMPORARILY ERODED MOST OF THE CONVECTION. HOWEVER...THE
DRY AIR ENTRAINMENT IS EXPECTED TO DECREASE AS THE MID- TO
UPPER-LEVEL FLOW GRADUALLY BACKS AROUND TO THE SOUTH-SOUTHEAST...
WHICH WILL BE ALONG THE FORECAST TRACK. THE GFDL BRINGS ARLENE UP
63 KT JUST BEFORE LANDFALL WHILE THE SHIPS MODEL ONLY STRENGTHENS
THE CYCLONE TO 45 KT. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF
THESE MODELS. HOWEVER...GIVEN THAT THE UPPER-LEVEL FLOW IS FORECAST
TO DECREASE TO LESS THAN 15 KT WHILE CONTINUING TO BACK...AND THAT
SSTS ARE EXPECTED TO BE 28-29C UNTIL LANDFALL BASED ON CURRENT BUOY
OBSERVATIONS...ARLENE COULD PEAK A LITTLE STRONGER BETWEEN 36-48
HOURS BEFORE WEAKENING BEGINS WHEN UPPER-LEVEL SHEAR INCREASES FROM
THE SOUTHWEST AS THE CYCLONE NEARS THE U.S. GULF COAST.
 
FORECASTER STEWART
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0300Z 20.8N  84.3W    35 KT
 12HR VT     10/1200Z 22.6N  85.0W    40 KT
 24HR VT     11/0000Z 25.0N  86.3W    45 KT
 36HR VT     11/1200Z 27.7N  87.9W    50 KT
 48HR VT     12/0000Z 30.5N  88.6W    55 KT...NEAR MS/AL COAST
 72HR VT     13/0000Z 36.0N  87.0W    20 KT...DISSIPATING INLAND
 96HR VT     14/0000Z 41.0N  82.5W    15 KT...REMNANT LOW INLAND
120HR VT     15/0000Z...DISSIPATED INLAND 
 
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