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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER 7
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT MON SEP 23 2002
THE CYCLONE CONTINUES TO PRODUCE A LARGE CLUSTER OF DEEP CONVECTION.
HOWEVER...IT IS BELIEVED THAT THE LOW LEVEL CENTER REMAINS WEST OF
THE CONVECTION. THERE IS ALSO SOME QUESTION AS TO WHETHER THE
CIRCULATION IS CLOSED AS QUIKSCAT DATA FROM LAST EVENING INDICATED
THE DEPRESSION MAY BE AN OPEN WAVE. BECAUSE OF THESE UNCERTAINTIES
THE SYSTEM WILL REMAIN A 30 KT DEPRESSION. A RECONNAISSANCE PLANE
WILL INVESTIGATE THE SYSTEM LATER THIS MORNING TO ANSWER THESE
QUESTIONS. IF THE PLANE FINDS A TROPICAL STORM IT WILL REQUIRE US
TO UPGRADE THE TROPICAL STORM WATCHES TO WARNINGS QUICKLY.
THE SYSTEM IS BEING STEERED WESTWARD BY A MID LEVEL RIDGE TO THE
NORTH AND THE INITIAL MOTION IS ESTIMATED TO BE 280/20 KT. THE
LATEST GFS MODEL SHIFTED THE FORECAST TRACK WELL NORTH OF THE
PREVIOUS RUN. THE GFS SOLUTION MAY BE INFLUENCED BY A WEAKNESS IN
THE RIDGE CAUSED BY TROPICAL STORM KYLE. IN ANY CASE...MOST OF THE
MODEL GUIDANCE SLOW THE SYSTEM DOWN IN ABOUT 48 HOURS...AS DOES THE
OFFICIAL FORECAST. THE OFFICIAL FORECAST IS NEAR THE SOUTHERN
EDGE OF THE MODEL ENVELOPE AND CLOSER TO THE GFDL AND THE PREVIOUS
ADVISORY.
THE OUTFLOW REMAINS IMPRESSIVE IN THE NORTHERN SEMICIRCLE AND THE
SHIPS INTENSITY MODEL FORECASTS A LOW SHEAR ENVIRONMENT. ASSUMING
THAT THE PLANE FINDS A CLOSED CIRCULATION....THE FORECAST IS FOR
GRADUAL STRENGTHENING WHICH IS CONSISTENT WITH THE PREVIOUS ADVISORY
BUT IS LESS AGGRESSIVE THAN THE SHIPS MODEL.
FORECASTER JARVINEN/BROWN
FORECAST POSITIONS AND MAX WINDS
INITIAL 23/0900Z 12.7N 58.4W 30 KTS
12HR VT 23/1800Z 13.2N 61.4W 35 KTS
24HR VT 24/0600Z 14.0N 64.6W 40 KTS
36HR VT 24/1800Z 14.8N 67.2W 50 KTS
48HR VT 25/0600Z 15.6N 69.3W 55 KTS
72HR VT 26/0600Z 17.0N 72.5W 65 KTS
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