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TROPICAL STORM JERRY DISCUSSION NUMBER   4
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SUN OCT 07 2001
 
SATELLITE IMAGERY AFTER THE ECLIPSE PERIOD ENDED SUGGESTS THAT JERRY 
HAS COMPLETED THE CONVECTIVE BURSTING PHASE. THERE STILL REMAINS 
SOME UNCERTAINTY CONCERNING THE EXACT LOCATION OF THE LOW-LEVEL 
CENTER...WHICH I FEEL IS ON THE EAST SIDE OF THE DEEPEST CONVECTION. 
THIS IS CLOSE TO THE CENTER OF CLOUD SYSTEM AND MAINTAINS CONTINUITY 
WITH THE PREVIOUS FORECAST TRACKS AND A FEW SHIP REPORTS TO THE 
NORTH OF JERRY. THE INITIAL INTENSITY WAS INCREASED TO 40 KT BASED 
DVORAK SATELLITE INTENSITY ESTIMATES OF 45 KT...T3.0...FROM TAFB... 
AND 35 KT...T2.5...FROM SAB AND AFWA.  THE UPPER-LEVEL OUTFLOW 
PATTERN IS FAIR TO GOOD IN ALL QUADRANTS.
 
THE INITIAL MOTION ESTIMATE IS 280/16.  THERE IS NO SIGNIFICANT 
CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING.  THE FORWARD 
MOTION WAS INCREASED THROUGH 24 HOURS...WITH A GRADUAL DECREASE IN 
FORWARD SPEED AFTER THAT.  THERE IS NOW EXCELLENT AGREEMENT AMONG 
THE GFDL AND THE GLOBAL MODELS...EXCEPT FOR THE AVN.  THE AVN MODEL 
IS FARTHER TO THE LEFT THAN THE PREVIOUS RUNS...BUT STILL TAKES 
JERRY NORTHWEST FROM ITS CURRENT POSITION AND WEAKENS THE SYSTEM 
BEFORE IT MOVES THE CYCLONE THROUGH THE LEEWARD ISLANDS IN 24 HOURS. 
THE AVN STILL APPEARS TO HAVE A STRONG POLEWARD BIAS...SO THIS 
SOLUTION WAS DISCOUNTED AGAIN.  THE GFDL...NOGAPS...AND UKMET MODELS 
ARE WITHIN 60 NM OF EACH OTHER THROUGH THE FORECAST PERIOD AND THOSE 
THREE MODELS MAINTAIN THE STRONG SUBTROPICAL RIDGE TO THE NORTH OF 
THE CARIBBEAN ISLANDS.  FOR THIS REASON...THE OFFICIAL TRACK IS JUST 
AN EXTENSION OF THE PREVIOUS FORECAST...ONLY A LITTLE FASTER.
 
THE INTENSITY FORECAST IS SOMEWHAT TRICKY. IT IS NOT UNCOMMON FOR 
SOME SLIGHT WEAKENING TO OCCUR AFTER A DEEP CONVECTIVE BURST ENDS.  
HOWEVER...A TIGHT INNER-CIRCULATION SHOULD REMAIN...WHICH COULD ACT 
TO FIRE UP MORE DEEP CONVECTION LATER TODAY AND TONIGHT.  THE 
UPPER-LEVEL ENVIRONMENT REMAINS FAVORABLE FOR CONTINUED 
STRENGTHENING...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST WHICH 
IS A BLEND BETWEEN THE SHIPS AND GFDL INTENSITY MODEL.  THE GFDL 
MODEL ACTUALLY BRINGS JERRY UP TO 90 TO 100 KT IN 72 HOURS AS THE 
CYCLONE IS APPROACHING JAMAICA AND HAITI.  HOWEVER...THE GFDL HAS 
HAD A HIGH INTENSITY BIAS SO FAR THIS YEAR...SO LESS WEIGHT WAS 
PLACED ON THAT INTENSITY FORECAST.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     07/0900Z 11.5N  56.2W    40 KTS
12HR VT     07/1800Z 11.9N  58.3W    45 KTS
24HR VT     08/0600Z 12.8N  61.2W    50 KTS
36HR VT     08/1800Z 13.8N  63.9W    55 KTS
48HR VT     09/0600Z 14.6N  66.4W    60 KTS
72HR VT     10/0600Z 16.5N  71.0W    70 KTS
 
 
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