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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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