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TROPICAL STORM ERIN DISCUSSION NUMBER  10
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT MON SEP 03 2001

OVER THE PAST SEVERAL HOURS...A BURST OF DEEP CONVECTION OCCURRED 
NEAR AND NORTHEAST OF THE LOW-LEVEL CENTER...AND THE HIGH CLOUDS ARE 
OBSCURING THE CENTER.  SUCH BURSTS OF CONVECTION DO NOT ALWAYS 
CORRESPOND TO INTENSIFICATION.  IN FACT...A SIMILAR EVENT WAS 
OBSERVED LAST NIGHT...JUST BEFORE ERINS STRUCTURE DETERIORATED 
MARKEDLY.  THE COLD-TOPPED CLOUDS HAVE AN AMORPHOUS SHAPE...AND 
DVORAK T-NUMBERS FROM TAFB AND SAB HAVE NOT INCREASED.  THEREFORE 
CURRENT INTENSITY IS HELD AT 40 KNOTS.  THE  SHEAR OVER ERIN HAS 
BEEN LARGELY PRODUCED BY STRONG LOW/MID-LEVEL FLOW AND 
MODERATE...GENERALLY SOUTHERLY...FLOW ALOFT.  LATEST WATER VAPOR 
IMAGES SHOW A CUT-OFF UPPER-LEVEL LOW NEAR 21N 58W...AND THIS 
FEATURE HAS BEEN MOVING LITTLE.  UNLESS THIS LOW BEGINS TO MOVE 
FARTHER AWAY FROM ERIN...OR WEAKEN...THE FLOW ASSOCIATED WITH THE 
UPPER LOW SHOULD INCREASE THE SHEAR ON THE TROPICAL CYCLONE.  
INTERESTINGLY THE NCEP GLOBAL...AVN...MODEL SHOWS THE UPPER LOW 
DISSIPATING IN A COUPLE OF DAYS.  HOWEVER...THIS MODEL HAS A HISTORY 
OF WEAKENING UPPER-LEVEL CYCLONIC FLOW TOO QUICKLY.  THE OFFICIAL 
INTENSITY FORECAST ALLOWS FOR THE POSSIBILITY THAT THE SHEAR WILL 
ABATE LATER IN THE PERIOD...BUT IS CONSERVATIVE.
 
MOTION ESTIMATE REMAINS THE SAME AS BEFORE...285/16.  ERIN CONTINUES 
TO BE STEERED BY A SUBSTANTIAL MID-LEVEL RIDGE TO ITS NORTH. A 
MID-LATITUDE TROUGH THAT IS FORECAST TO MOVE OFF THE NORTHEAST U.S. 
COAST IN A DAY OR SO SHOULD WEAKEN THIS RIDGE A BIT.  THE TRACK 
GUIDANCE MODELS RESPOND TO THIS BY BENDING ERINS HEADING GENTLY TO 
THE RIGHT.  THE OFFICIAL FORECAST FOLLOWS SUIT...BUT REMAINS BIASED 
TOWARDS THE SOUTHERNMOST MODEL TRACKS.  THIS IS VERY CLOSE TO THE 
LATEST AVN AND FSU SUPERENSEMBLE OUTPUT.

FORECASTER PASCH/MOLLEDA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     04/0300Z 16.9N  49.4W    40 KTS
12HR VT     04/1200Z 17.5N  51.7W    40 KTS
24HR VT     05/0000Z 18.6N  54.5W    45 KTS
36HR VT     05/1200Z 19.8N  57.0W    50 KTS
48HR VT     06/0000Z 21.0N  59.0W    55 KTS
72HR VT     07/0000Z 23.0N  61.5W    60 KTS
 
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