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TROPICAL STORM ERIN DISCUSSION NUMBER  15
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT WED SEP 05 2001
 
ERIN HAS CHANGED LITTLE OVERNIGHT WITH JUST THE USUAL NOCTURNAL 
CONVECTIVE FLAREUP. THE EXACT LOCATION OF THE BROAD AND ELONGATED 
CENTER IS DIFFICULT TO ASCERTAIN USING CONVENTIONAL SATELLITE DATA.  
HOWEVER...EXTRAPOLATION OF THE MID-LEVEL CIRCUALTION IN SSMI AND 
TRMM MICROWAVE DATA SUPPORTS KEEPING THE CENTER NEAR THE WESTERN 
EDGE OF THE CONVECTIVE CLOUD SHIELD.  THE INITIAL INTENSITY WAS KEPT 
AT 45 KT EVEN THOUGH SATELLITE INTENSITY ESTIMATES SUGGEST THAT ERIN 
HAS WEAKENED.  RECON WILL BE OUT TO INVESTIGATE THE CYCLONE AROUND 
1200Z AND SHOULD PROVIDE A MUCH BETTER ASSESSMENT OF THE ACTUAL 
STRENGTH AND LOCATION OF THE LOW-LEVEL CIRCULATION.

THE INITIAL MOTION ESTIMATE IS 285/16.  FOR THE PAST 4 DAYS...ERIN 
HAS BASICALLY BEEN TRACKING ALONG A 285 DEGREES DIRECTION.  THE MID- 
AND UPPER-LEVEL CIRCULATION REMAIN TILTED BACK TO THE NORTHEAST... 
BUT THIS NOW APPEARS DUE MORE TO LOW-LEVEL EASTERLY SHEAR AND NOT 
UPPER-LEVEL SOUTHWESTERLY SHEAR.  IT IS POSSIBLE THAT THE LOW-LEVEL 
CENTER MAY RE-DEVELOP FARTHER NORTH CLOSER TO THE DEEP CONVECTION.  
EITHER WAY...THE MOST SIGNIFICANT WINDS WOULD REMAIN NORTH OF THE 
LEEWARD ISLANDS. THE NHC MODEL GUIDANCE IS EVEN MORE DIVERGENT NOW 
BEYOND 36 HOURS.  THE AVN MODEL HAS BECOME THE RIGHT OR EASTERNMOST 
MODEL...WHILE THE UKMET MODEL HAS CONTINUED TO SHIFT THE FORECAST 
TRACK MORE TO THE LEFT AS IT HAS EACH MODEL RUN THE PAST 4 DAYS.  
THE LATEST NOGAPS MODEL IS NOW THE MOST OMINOUS OF ALL THE MODELS 
AND TAKES ERIN MORE WESTWARD AND AIMS THE CYCLONE TOWARD THE 
NORTHERN BAHAMAS BY 72 HOURS.  THE OFFICIAL FORECAST TRACK IS 
BETWEEN THE GUNS AND GUNA MODEL ENSEMBLES AND A LITTLE TO THE LEFT 
OF THE PREVIOUS FORECAST. NOTE...IT IS POSSIBLE THAT ERIN COULD GET 
TRAPPED IN THE MID-LEVEL RIDGE FORECAST BY ALL OF THE GLOBAL MODELS 
AND THE ETA MODEL TO BUILD ALONG THE U.S. EAST COAST IN 72 HOURS. 
THIS WOULD RESULT IN THE CYCLONE BECOMING STATIONARY OR TO MOVE 
ERRATICALLY.

UNTIL THE LOW-LEVEL CENTER REMAINS VERTICALLY ALIGNED WITH THE MID- 
AND UPPER-LEVEL CIRCULATION...NO SIGNIFICANT INTENSIFICATION WILL 
OCCUR.  NO CHANGE WAS MADE TO THE PREVIOUS INTENSITY FORECAST...BUT  
BY 36 HOURS...THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BECOME MORE 
FAVORABLE FOR STRENGTHENING TO OCCUR.  HOWEVER...INTENSIFICATION MAY 
END UP BEING MORE A REUSLT OF THE SYSTEM SLOWING DOWN AND ALLOWING 
THE LOW-LEVEL CIRCULATION TO TUCK IN MORE UNDER THE DEEP CONVECTION.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     05/0900Z 18.3N  57.3W    45 KTS
12HR VT     05/1800Z 19.4N  59.5W    45 KTS
24HR VT     06/0600Z 20.7N  61.4W    45 KTS
36HR VT     06/1800Z 22.0N  62.7W    55 KTS
48HR VT     07/0600Z 23.2N  64.0W    60 KTS
72HR VT     08/0600Z 24.5N  65.5W    65 KTS
 
 
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