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TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   7
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT THU SEP 13 2001
 
AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT DEVELOPED MECHANICAL
PROBLEMS ENROUTE TO TROPICAL DEPRESSION EIGHT AND HAD TO TURN
BACK...  SO NO IN-SITU DATA WAS AVAILABLE FOR THIS ADVISORY.
HOWEVER...DOPPLER RADAR DATA FROM KEY WEST ALONG WITH INFRARED
SATELLITE DATA INDICATE THAT THE DEPRESSION HAS CONTINUED TO BECOME
BETTER ORGANIZED.  DEEP CONVECTION HAS FINALLY DEVELOPED AND
PERSISTED NEAR THE LOW-LEVEL CENTER...WHICH REMAINS SITUATED JUST
SOUTH OR SOUTHEAST OF EAST GULF BUOY 42003.  AT 13/06Z SHIP
WPKD...LOCATED ABOUT 70 NM SOUTHEAST OF THE CENTER...REPORTED A 32
KT SUSTAINED WIND AND A PRESSURE OF 1006 MB...WHICH SUGGESTS THAT
THIS SYSTEM IS NEAR TROPICAL STORM STRENGTH.  UPPER-LEVEL OUTFLOW IS
GOOD IN THE SOUTHEAST SEMICIRCLE...BUT IS RESTRICTED TO THE
NORTHWEST DUE TO MODERATE UPPER-LEVEL SHEAR.

THE INITIAL MOTION ESTIMATE IS QUASI-STATIONARY.  THERE REMAINS
CONSIDERABLE DIVERGENCE AMONG THE VARIOUS NHC FORECAST MODELS...
ESPECIALLY AMONG THE GLOBAL MODELS.  NOGAPS AND THE UKMET MODELS
CONTINUE TO TAKE THE DEPRESSION SLOWLY WEST OR WEST-SOUTHWESTWARD...
WHILE THE AVN...GFDL...AND GFDN MODELS KEEP THE CYCLONE
QUASI-STATIONARY FOR ABOUT 24 HOURS AND THEN SLOWLY MOVE IT
NORTHEASTWARD TOWARD THE WEST COAST OF THE FLORIDA PENINSULA AS A
RATHER FORMIDABLE TROPICAL CYCLONE.  BY 72 HOURS...THE UKMET MODEL
BEGINS TO TAKE THE CYCLONE TOWARD THE NORTHEAST...WHILE THE AVN
MODEL TAKES THE DEPRESSION INLAND NEAR THE CEDAR KEY FLORIDA AREA IN
ABOUT 72 HOURS.  THE GFDN AND GFDL MODELS TAKE THE CYCLONE INLAND
ALONG THE FLORIDA WEST COAST OVER OR JUST NORTH OF TAMPA BAY IN
ABOUT 60 HOURS.  THE STRONG HIGH PRESSURE RIDGE OVER THE SOUTHERN
PLAINS AND NORTHERN MEXICO SHOULD AMPLIFY AND BECOME MORE MERIDIONAL
AS THE U.S.  WEST COAST TROUGH LIFTS NORTHWARD OVER THE TOP OF THE
RIDGE.  THIS SHOULD HELP TO PRECLUDE ANY SIGNIFICANT WESTWARD MOTION
AND KEEP THE CYCLONE IN WEAK STEERING FLOW FOR THE NEXT 36 HOURS.
AS ANOTHER SHORTWAVE TROUGHS DIGS SOUTHEASTWARD INTO THE SOUTHEAST
U.S.  LONGWAVE TROUGH...THE CYCLONE SHOULD BE NUDGE SLOWLY
NORTHEASTWARD IN 48 TO 72 HOURS.  THIS SCENARIO IS CONSISTENT WITH
THE CURRENT LONGWAVE TROUGH-RIDGE PATTERN AND THE AVN-GFDL-UKMET
MODELS.

ALL OF THE GLOBAL MODELS CONTINUE THE TREND OF LIFTING OUT THE
UPPER-LEVEL SHORTWAVE TROUGH THAT IS CURRENTLY OVER THE SOUTHEAST
U.S...  WHICH RESULTS IN A SIGNIFICANT DECREASE IN THE UPPER-LEVEL
SHEAR BY 36 HOURS...IF THE CYCLONE REMAINS AT OR NEAR ITS CURRENT
LOW LATITUDE.  GIVEN THAT NONE OF THE MODELS TAKE THE DEPRESSION
MUCH FARTHER NORTH THAN THAN 27N LATITUDE IN 36 HOURS...
STRENGTHENING APPEARS LIKELY OWING TO THE DECREASING SHEAR PATTERN.
BY 48 HOURS...ANOTHER SHORTWAVE DROPS DOWN TO RE-INFORCE THE
UPPER-LEVEL LONGWAVE TROUGH...WHICH RESULTS IN AN INCREASE IN THE
JETSTREAM WIND SPEEDS FROM NORTH CAROLINA SOUTHWESTWARD TO NORTH
FLORIDA.  THE PROXIMITY OF THE CYCLONE TO THE RIGHT-REAR JET
ENTRANCE REGION SHOULD ENHANCE THE OUTFLOW AND MASS DIVERGENCE IN
THE NORTHERN SEMICIRCLE...WHICH FURTHER SUGGESTS THAT
INTENSIFICATION IS PROBABLE.  THE OFFICIAL INTENSITY FORECAST IS A
LITTLE HIGHER THAN THE SHIPS INTENSITY MODEL BASED ON THE NEAR
30C SSTS THAT THE CYCLONE WILL REMAIN OVER THROUGHOUT THE FORECAST
PERIOD.  IT SHOULD BE NOTED THAT THE GFDL MODEL BRINGS THIS SYSTEM
UP TO 100 KT JUST PRIOR TO ITS FORECAST LANDFALL.

FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     13/0900Z 25.2N  85.8W    30 KTS
12HR VT     13/1800Z 25.2N  85.9W    35 KTS
24HR VT     14/0600Z 25.6N  86.2W    40 KTS
36HR VT     14/1800Z 26.2N  86.2W    50 KTS
48HR VT     15/0600Z 27.0N  85.8W    65 KTS
72HR VT     16/0600Z 28.5N  83.5W    75 KTS
 
 
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