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HURRICANE GERT DISCUSSION NUMBER  16
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT WED SEP 15 1999
 
GERT CONTINUES TO LOOK IMPRESSIVE ON INFRARED SATELLITE IMAGERY WITH
CLOUDS TOPS TO -80C SURROUNDING THE EYE. THE EYE IS NOT YET THAT
WELL DEVELOPED...SO SATELLITE INTENSITY ESTIMATES FROM SAB...TAFB...
AND AFWA REMAIN AT 115 KT...102 KT...AND 102 KT RESPECTIVELY. THE
MAXIMUM INTENSITY REMAINS AT 110 KT FOR THIS ADVISORY.

THE INITIAL MOTION IS LITTLE CHANGED AT 280/11. WATER VAPOR IMAGERY
INDICATES THAT GERT IS CURRENTLY MOVING WESTWARD UNDER A STRONG
SUBTROPICAL RIDGE. HOWEVER...AN UPPER LEVEL LOW IS LOCATED NEAR 27N
60W...AND HURRICANE FLOYD AND A STRONG MID/UPPER LEVEL TROUGH ARE
NEAR AND OVER THE EASTERN U.S.. LARGER SCALE MODELS INDICATES A
COMBINATION OF THESE FEATURES WILL CREATE A LARGE WEAKNESS OR BREAK
IN THE SUBTROPICAL RIDGE BY THE END OF THE FORECAST PERIOD. ALL
GUIDANCE RESPONDS TO THIS BY TURNING THE HURRICANE NORTHWEST BY 72
HOURS. THE OFFICIAL FORECAST TRACK FOLLOWS THIS IDEA...BUT IS ALONG
THE SOUTHERN EDGE OF THE GUIDANCE. THIS IN CASE THE WEAKNESS IS NOT
AS PRONOUNCED AS CURRENTLY FORECAST...OR IN CASE THE HURRICANE
ITSELF BUILDS THE RIDGE FARTHER WESTWARD.
 
GERT CURRENTLY SHOWS GOOD OUTFLOW IN ALL DIRECTIONS. THIS COMBINED
WITH THE STILL-DEVELOPING EYE AND COLD CONVECTIVE TOPS INDICATES
CONTINUED STRENGTHENING...AT LEAST FOR A DAY OR SO. AFTER THAT
TIME...INCREASING VERTICAL SHEAR ASSOCIATED WITH THE UPPER LEVEL LOW
MAY STOP DEVELOPMENT OR CAUSE A SLIGHT WEAKENING...AS SUGGESTED BY
THE SHIPS MODEL. THE OFFICIAL FORECAST BRINGS GERT TO 120 KT IN 24
HOURS FOLLOWED BY A SLIGHT WEAKENING. THERE IS A CHANCE THAT GERT
COULD STRENGTHEN FASTER THAN FORECAST DURING THE FIRST 24 TO 36
HOURS.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     15/0900Z 17.6N  48.5W   110 KTS
12HR VT     15/1800Z 17.9N  50.2W   115 KTS
24HR VT     16/0600Z 18.5N  52.4W   120 KTS
36HR VT     16/1800Z 19.4N  54.7W   120 KTS
48HR VT     17/0600Z 20.5N  57.0W   115 KTS
72HR VT     18/0600Z 23.5N  60.5W   115 KTS
 
 
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