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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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