HOME	ACTIVE CYCLONES	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
HURRICANE GERT DISCUSSION NUMBER  28
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SAT SEP 18 1999
 
THERE HAS BEEN LITTLE CHANGE IN THE CONVECTIVE STRUCTURE OF GERT
DURING THE NIGHT...AS THE CENTRAL CONVECTION REMAINS SOMEWHAT
ASYMMETRIC AND THE EYE SOMEWHAT RAGGED. SATELLITE INTENSITY
ESTIMATES FROM SAB...TAFB...AND AFWA ARE 115 KT...102 KT...AND 102
KT. THE INITIAL INTENSITY REMAINS AT 110 KT FOR THIS ADVISORY.

THE HURRICANE HAS TURNED A LITTLE MORE TO THE RIGHT DURING THE NIGHT
AND THE 12 HOUR MOTION IS NOW 330/08...WHICH IS THE INITIAL MOTION
FOR THIS PACKAGE. THE SHORT TERM MOTION APPEARS TO BE EVEN MORE
NORTHERLY. SATELLITE IMAGERY INDICATES AN UPPER LEVEL TROUGH AND
SURFACE FRONTAL TROUGH...ASSOCIATED WITH EX-HURRICANE FLOYD...  
NORTHWEST OF GERT...AND AN UPPER LEVEL RIDGE JUST EAST OF THE
FRONTAL TROUGH. CURRENT TRENDS AND THE VARIOUS MODELS SUGGEST GERT
IS MOVING SLOWLY ENOUGH THAT IT WILL NOT BE ABLE TO GET EAST OF THE
FRONTAL TROUGH. THUS...LOW LEVEL RIDGING MAY INCREASE NORTH OF THE
HURRICANE AFTER ABOUT 24 HOURS. SEVERAL MODELS...INCLUDING THE
GFDL...PICK UP ON THIS AND BEND THE FORECAST TRACKS A LITTLE TO THE
LEFT BETWEEN 24 AND 48 HOURS. THIS IS FOLLOWED BY A MORE NORTHERLY
MOTION AS THE RIDGE WEAKENS IN ADVANCE OF A NEW DEEP LAYER TROUGH
DEVELOPING OVER THE EASTERN U.S.. THE OFFICIAL FORECAST REFLECTS
THIS SCENARIO...WITH A GRADUAL TURN TO THE NORTHWEST IN THE FIRST 26
HOURS AND A MORE NORTHERLY MOTION AFTER 48 HOURS.

THE UPPER-TROPOSPHERIC OUTFLOW CONTINUES TO BE RESTRICTED TO THE
WEST...LIKELY DUE TO THE NORTHEAST-SOUTHWEST ORIENTED UPPER TROUGH
SITUATED ABOUT 10 DEGREES TO THE WEST OF GERT. HOWEVER...THE AVN AND
NOGAPS SUGGEST THE TROUGH WILL WEAKEN AND AN ANTICYCLONE BUILD OVER
THE HURRICANE. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS
PACKAGE...CALLING FOR LITTLE CHANGE IN STRENGTH. HOWEVER...AN
ALTERNATE SCENARIO WOULD BE WEAKENING IN THE FIRST 24 HOURS FOLLOWED
BY SOME INTENSIFICATION IF THE UPPER LEVEL ENVIRONMENT IMPROVES AS
THE MODELS FORECAST.

INTEREST IN BERMUDA SHOULD CONTINUE TO MONITOR THE PROGRESS OF GERT.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/0900Z 22.2N  57.4W   110 KTS
12HR VT     18/1800Z 23.3N  58.0W   110 KTS
24HR VT     19/0600Z 24.8N  59.1W   105 KTS
36HR VT     19/1800Z 26.2N  60.4W   105 KTS
48HR VT     20/0600Z 27.5N  62.0W   105 KTS
72HR VT     21/0600Z 30.0N  64.0W   105 KTS
 
 
NNNN