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TROPICAL STORM ERIN DISCUSSION NUMBER   6
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT SUN SEP 02 2001

ERIN HAS FAILED TO BECOME BETTER ORGANIZED...IN SPITE OF RATHER 
HEALTHY-LOOKING UPPER-LEVEL OUTFLOW AND RELATIVELY WEAK SHEAR.  IR 
IMAGES SHOWED A BURST OF DEEP CONVECTION NEAR...OR JUST NORTH 
OF...THE ESTIMATED CENTER...BUT THE INNER-CORE OF THE TROPICAL 
CYCLONE REMAINS POORLY ORGANIZED.  THERE IS AN UPPER-LEVEL TROUGH 
LOCATED ABOUT 15 DEGREES WEST-NORTHWEST OF ERIN...I.E. IN THE PATH 
OF THE TROPICAL CYCLONE.  THE NCEP GLOBAL MODEL INDICATES THAT AN 
UPPER-LEVEL LOW WILL CUT OFF FROM THIS TROUGH...IN THE VICINITY OF 
21N 55W...WITHIN 12 HOURS OR SO...AND WATER VAPOR IMAGERY ALSO 
SUGGESTS THAT THIS IS BEGINNING TO HAPPEN.  IF THE LOW IS FAIRLY 
LARGE IN COMPARISON TO THE TROPICAL CYCLONE...AND DOES NOT MOVE 
MUCH...THERE WILL BE A SIGNIFICANT INCREASE IN THE SHEAR OVER ERIN.  
THE SHIPS MODEL...WHICH IS BASED ON THE GLOBAL MODEL FORECAST 
WINDS...SHOWS SOME INCREASE IN THE SHEAR BUT NOT ENOUGH TO PREVENT A 
MODEST AMOUNT OF STRENGTHENING.  THE OFFICIAL FORECAST GOES ALONG 
WITH THIS IDEA.  HOWEVER IT SHOULD BE NOTED THAT THE EXPLICIT 
INTENSITY FORECAST FROM THE NCEP GLOBAL MODEL...WHICH APPEARS TO 
HAVE SOME SKILL IN PREDICTING INTENSITY TRENDS...SHOWS ERIN 
WEAKENING.

THE CENTER LOCATION IS NOT OBVIOUS.  AN SSM/I OVERPASS AT 2320Z
SUGGESTED THAT THE CENTER MAY BE SOMEWHAT TO THE NORTH OF PREVIOUS
ESTIMATES.  HOWEVER...TO MAINTAIN CONTINUITY WITH THE PREVIOUS
TRACK...I AM LEANING MORE TOWARD THE POSITION ESTIMATE PROVIDED BY
TAFB.  THIS GIVES AN INITIAL MOTION OF 290/14.  A MID-TROPOSPHERIC
RIDGE TO THE NORTH OF ERIN CONTINUES TO BE THE PRIMARY STEERING
MECHANISM.  IN 2-3 DAYS...A MID-LATITUDE TROUGH MOVING OFF THE
NORTHEAST U.S. COAST WILL PROBABLY WEAKEN THE RIDGE SOMEWHAT.    THE
OFFICIAL FORECAST TRACK IS ADJUSTED ONLY SLIGHTLY TO THE NORTH OF
THE PREVIOUS ONE...BUT IS STILL ON THE SOUTH SIDE OF THE NUMERICAL
GUIDANCE ENVELOPE.  THE ONLY EXCEPTION/OUTLIER IS THE GFDL MODEL...
WHICH IS A DEGREE OR TWO TO THE SOUTH OF THE NHC TRACK.

FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     03/0300Z 14.8N  42.5W    45 KTS
12HR VT     03/1200Z 15.4N  44.6W    50 KTS
24HR VT     04/0000Z 16.3N  47.3W    55 KTS
36HR VT     04/1200Z 17.2N  50.0W    60 KTS
48HR VT     05/0000Z 18.2N  52.5W    60 KTS
72HR VT     06/0000Z 20.0N  56.5W    65 KTS
 
 
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