Tropical Depression 17: Discussion #1

TROPICAL DEPRESSION SEVENTEEN DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172008
400 PM EST WED NOV 05 2008

THE AREA OF DISTURBED WEATHER IN THE SOUTHWESTERN CARIBBEAN SEA HAS
DEVELOPED ENOUGH ORGANIZED CONVECTION AND LOW-LEVEL CIRCULATION TO
BE CONSIDERED A TROPICAL DEPRESSION. AN AIR FORCE HURRICANE HUNTER
FOUND MAXIMUM WINDS OF 26 KT AT 1000 FT WITH A MINIMUM PRESSURE OF
1004 MB. SATELLITE IMAGES SHOW THAT MOST OF THE CONVECTION IS
NORTHWEST OF THE CENTER BUT IS STARTING TO TAKE ON A BANDED
APPEARANCE. THE INITIAL INTENSITY IS SET TO 25 KT IN ACCORDANCE
WITH THE AIRCRAFT DATA AND NOAA BUOY 42057.

ATMOSPHERIC AND OCEANIC PARAMETERS APPEAR TO BE VERY FAVORABLE FOR
STRENGTHENING DURING THE NEXT COUPLE OF DAYS. IN FACT...THE GFDL
AND HWRF TURN THE DEPRESSION INTO A MAJOR HURRICANE BEFORE CROSSING
CUBA. IN CONTRAST...THE SHIPS/LGEM MODELS KEEP THE SYSTEM BELOW
HURRICANE STRENGTH...WHICH SEEMS A LITTLE UNDERDONE GIVEN A LARGE
UPPER ANTICYCLONE THAT ALL OF THE GLOBAL MODELS ARE FORMING NEAR
THE DEPRESSION. THE OFFICIAL FORECAST WILL BE CLOSER TO THE
DYNAMICAL GUIDANCE BUT NOT QUITE AS BULLISH AS THOSE MODELS FOR THE
TIME BEING. NEAR THE END OF THE PERIOD...VERTICAL SHEAR IS
FORECAST TO INCREASE DRAMATICALLY AND THIS COULD RESULT IN AN
ABRUPT WEAKENING.

A TWELVE-HOUR MOTION OF THIS SYSTEM IS ESTIMATED AT 305/4. A SLOW
NORTHWEST TO NORTH MOVEMENT IS EXPECTED DURING THE NEXT DAY OR TWO
AS THE DEPRESSION IS STEERED AROUND SOUTHWESTERN SIDE OF A MID-
TROPOSPHERIC HIGH OVER THE NORTH-CENTRAL CARIBBEAN SEA. A DEEP
TROUGH IS EXPECTED TO MOVE INTO THE GULF OF MEXICO IN ABOUT 3
DAYS...WHICH SHOULD CAUSE THE CYCLONE TO TURN TOWARD THE NORTHEAST
AND ACCELERATE. THERE ARE SOME SIGNIFICANT SPEED DISCREPANCIES IN
THE MODELS WITH THE GFDL/HWRF CONSIDERABLY FASTER THAN THE
GFS/ECMWF/UKMET MODELS. LATE-SEASON TROPICAL CYCLONES ARE OFTEN
NOTORIOUSLY SLOW-MOVING...E.G. MITCH OR WILMA...AND THE MODELS CAN
BE TOO QUICK TO EJECT THESE SYSTEMS OUT OF THE CARIBBEAN. WE'RE
GOING TO LEAN TOWARD THE SLOWER GUIDANCE AT THIS TIME...AND THE NHC
FORECAST IS A BIT BEHIND THE DYNAMICAL MODEL CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 05/2100Z 14.0N 81.8W 25 KT
12HR VT 06/0600Z 14.3N 82.2W 30 KT
24HR VT 06/1800Z 14.8N 82.5W 40 KT
36HR VT 07/0600Z 15.5N 82.9W 50 KT
48HR VT 07/1800Z 16.5N 83.0W 65 KT
72HR VT 08/1800Z 18.0N 82.5W 75 KT
96HR VT 09/1800Z 19.5N 80.0W 75 KT
120HR VT 10/1800Z 21.5N 75.5W 50 KT


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