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TROPICAL STORM ERIN DISCUSSION NUMBER 9
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT MON SEP 03 2001
THE INITIAL MOTION ESTIMATE IS 285/16. THE 12Z AVIATION MODEL
CONTINUES TO SHOW THE SAME SCENARIO...AN EAST/WEST RIDGE NORTH OF
THE STORM FORCING A GENERAL WEST-NORTHWESTWARD MOTION. AN
AMPLIFYING TROUGH IN THE WESTERLIES IS FORECAST TO MOVE TO ABOUT 60
DEGREES WEST IN 72 HOURS WHICH WILL WEAKEN THE RIDGE ENOUGH TO ALLOW
A LITTLE MORE NORTHWARD COMPONENT OF MOTION. THE OFFICIAL FORECAST
TRACK IS SIMILAR TO THE PREVIOUS ONE AND IS IN AGREEMENT WITH NOGAPS
AND THE AVIATION MODEL. THE GFDL MODEL IS A LITTLE TO THE LEFT AND
THE UKMET IS CONSIDERABLE RIGHT OF THE OFFICIAL FORECAST.
WITH THE DEEP CONVECTION SHEARED TO THE NORTHEAST OF THE EXPOSED
CENTER FROM AN UPPER LOW TO THE NORTHWEST... ERIN HAS WEAKENED.
THIS IS CONFIRMED BY A DRIFTING BUOY WHICH THE CENTER HAS PASSED
OVER. THE HIGHEST WINDS REPORTED BY THE BUOY WERE 31 KNOTS ALONG
WITH A 1003.9 MINIMUM PRESSURE. THE BUOY HAS NOT YET REPORTED FROM
UNDER THE DEEP CONVECTION AND IT IS ASSUMED THAT THE WINDS ARE NEAR
40 KNOTS UNDER THIS CONVECTION. THE CONVECTION HAD BEEN WARMING
UNTIL THE LAST COUPLE OF HOURS WHEN A NEW BURST BEGAN TO FORM
NORTHEAST OF THE CENTER. SO THE INITIAL WIND SPEED IS 40 KNOTS.
THE SHIPS MODEL BRINGS THE WIND TO 63 KNOTS IN 72 HOURS WITH
VERTICAL SHEAR 15 KNOTS OR LESS. THE GFDL MODEL IS QUITE AGGRESSIVE
WITH 103 KNOTS IN 72 HOURS. THE UKMET AND AVIATION MODEL SHOW
LITTLE STRENGTHENING. SO THE INTENSITY FORECAST IS A COMPROMISE 60
KNOTS IN 72 HOURS. SOME OF MY COLLEAGUES DO NOT THINK ERIN WILL
RECOVER FROM THE SHEARING THAT HAS OCCURRED. THEY MAY BE RIGHT.
FORECASTER LAWRENCE
FORECAST POSITIONS AND MAX WINDS
INITIAL 03/2100Z 16.4N 47.9W 40 KTS
12HR VT 04/0600Z 16.9N 50.3W 45 KTS
24HR VT 04/1800Z 17.7N 53.1W 50 KTS
36HR VT 05/0600Z 18.8N 55.8W 55 KTS
48HR VT 05/1800Z 20.2N 58.1W 60 KTS
72HR VT 06/1800Z 22.5N 60.5W 60 KTS
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