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TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER 4
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT FRI SEP 15 2000
THERE IS LITTLE EVIDENCE OF A LOW LEVEL CIRCULATION ON INFRARED
IMAGERY. THE IMAGERY DOES SUGGEST A MID LEVEL CIRCULATION NEAR THE
NORTH COAST OF THE YUCATAN PENINSULA...BUT THERE IS CONSIDERABLE
UNCERTAINTY ABOUT THE POSITION. THIS IS USUALLY THE CASE WITH WEAK
SYSTEMS AT NIGHT. THE GUIDANCE MODELS ARE SOMEWHAT DIVERGENT. THE
GFDL AND UKMET MODELS DRIFT THE DEPRESSION VERY SLOWLY OVER THE
SOUTH CENTRAL GULF FOR THREE DAYS. THE DEEP BAM AND LBAR SHOW A
MOTION TO THE NORTHEAST GULF AND THE REMAINDER OF THE MODELS SHOW A
NORTHWESTWARD DRIFT TO THE NORTH CENTRAL GULF. THE OFFICIAL
FORECAST TRACK IS SLOW NORTHWESTWARD SIMILAR TO THE PREVIOUS
ADVISORY AS A KIND OF CONSENSUS OF ALL OF THE GUIDANCE.
STRONG WESTERLIES ARE FORECAST NORTH OF 25N. SO THE DEPRESSION WILL
HAVE TO MOVE SLOWLY AND STAY SOUTH OF THE WESTERLY SHEAR IN ORDER TO
SURVIVE AND STRENGTHEN. THE SHIPS MODEL BRINGS THE WIND SPEED TO 69
KNOTS IN 72 HOURS AND THE OFFICIAL FORECAST IS TO 65 KNOTS FOLLOWING
THE PREVIOUS ADVISORY. THE SHIPS MODEL IS BELIEVED TO HAVE A
POSITIVE BIAS FOR DEPRESSION STAGE AS THE SHIPS DEVELOPMENTAL DATA
SET DID NOT CONTAIN DEPRESSIONS THAT DID NOT BECOME TROPICAL STORMS.
SO THE WIND SPEED FORECAST MAY BE A LITTLE TOO AGGRESSIVE.
AN AIRCRAFT IS SCHEDULED TO INVESTIGATE THE AREA A LITTLE LATER THIS
MORNING.
FORECASTER LAWRENCE
FORECAST POSITIONS AND MAX WINDS
INITIAL 15/0900Z 21.5N 88.0W 25 KTS
12HR VT 15/1800Z 21.9N 88.5W 30 KTS
24HR VT 16/0600Z 22.4N 89.2W 35 KTS
36HR VT 16/1800Z 22.9N 89.9W 40 KTS
48HR VT 17/0600Z 23.5N 90.5W 45 KTS
72HR VT 18/0600Z 24.5N 92.0W 65 KTS
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