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HURRICANE ERIN DISCUSSION NUMBER  30
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT SUN SEP 09 2001
 
THE HURRICANE HUNTERS JUST REPORTED 118 KT WINDS AT THE 700 MB
FLIGHT LEVEL.  USING OUR STANDARD REDUCTION FACTOR OF 90 PERCENT TO
GO FROM 700 MB TO THE SURFACE GIVES JUST OVER 105 KNOTS...I.E.  CAT.
3 ON THE SAFFIR-SIMPSON HURRICANE SCALE.  A GPS DROPSONDE RELEASED
IN THE NORTHEAST EYEWALL SHOWED A SPOT SURFACE WIND OF 111 KNOTS.
HOWEVER USING THE MORE CONSERVATIVE MEAN BOUNDARY LAYER WIND OR THE
AVERAGE WIND IN THE LOWEST 150 METERS OF THE SOUNDING GIVES A VALUE
CLOSER TO 100 KNOTS...SO 105 KNOTS IS A GOOD COMPROMISE.  EVEN
THOUGH THE REPORTED CENTRAL PRESSURE...968 MB...IS A LITTLE HIGHER
THAN WHAT ONE WOULD NORMALLY EXPECT FOR A HURRICANE OF THIS
STRENGTH...THE ENVIRONMENTAL PRESSURES ARE ALSO HIGHER THAN AVERAGE
IN THIS AREA.  NOT MUCH ADDITIONAL STRENGTHENING IS
ANTICIPATED...BUT SINCE SSTS DO NOT COOL MUCH ALONG THE TRACK OF
ERIN FOR THE NEXT DAY OR SO...ERIN SHOULD BE ABLE TO HOLD HER OWN
FOR A WHILE.  THE OFFICIAL INTENSITY FORECAST IS A LITTLE ABOVE THAT
SHOWN BY THE SHIPS MODEL.
 
INITIAL MOTION IS SLOWING AND TURNING A LITTLE TO THE RIGHT.  THE
MOVEMENT OF ERIN SHOULD SLOW EVEN MORE DURING THE NEXT 24 TO 36
HOURS...DUE TO A BLOCKING RIDGE IN THE MIDDLE TROPOSPHERE.  NEAR THE
END OF THE PERIOD...ERIN SHOULD BREAK THROUGH THE RIDGE AND START TO
MOVE FASTER TOWARD THE NORTHEAST.  THE OFFICIAL FORECAST IS SOMEWHAT
TO THE RIGHT OF THE PREVIOUS ONE...BUT ABOUT IN THE MIDDLE OF THE 
CURRENT OBJECTIVE GUIDANCE ENVELOPE.
 
FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     09/2100Z 32.9N  63.0W   105 KTS
12HR VT     10/0600Z 34.2N  64.0W   105 KTS
24HR VT     10/1800Z 35.6N  64.0W   100 KTS
36HR VT     11/0600Z 36.5N  64.0W    95 KTS
48HR VT     11/1800Z 37.5N  63.0W    85 KTS
72HR VT     12/1800Z 39.0N  60.0W    75 KTS
 
 
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