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Tropical Storm HANNA


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM HANNA DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
500 PM EDT WED SEP 03 2008
 
AN ASCAT PASS FROM 14Z REVEALED THAT THE LOW-LEVEL CIRCULATION OF
HANNA WAS BECOMING ELONGATED IN RESPONSE TO THE ASYMMETRIC
DISTRIBUTION OF CONVECTION.  IN SPITE OF THIS...DATA FROM THE
RECONNAISSANCE AIRCRAFT INDICATE THAT HANNA IS BECOMING A LITTLE
BETTER ORGANIZED.  TROPICAL STORM FORCE WINDS HAVE RETURNED TO THE
SOUTHWEST QUADRANT AND THE PRESSURE HAS FALLEN TO 989 MB.  THE
AIRCRAFT DATA CONTINUE TO SUGGEST THAT THE MAXIMUM WINDS ARE ABOUT
50 KT.

A MORE DEFINITIVE NORTHWARD MOTION HAS COMMENCED...WITH THE INITIAL
ESTIMATE BEING 360/10.   THE UPPER LOW OFF OF NEW ENGLAND IS
BEGINNING TO MOVE OUT...AND AS IT DOES SO MID-LEVEL RIDGING WILL
BUILD IN BEHIND IT.  HANNA SEEMS TO BE FOLLOWING THE CONVECTION
FAIRLY WELL...AND I'VE HAD TO SPEED UP MY PREVIOUS FORECAST A
LITTLE BIT.  THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH A
BLEND OF THE ECMWF AND THE GFS.  THE HWRF AND GFDL CONTINUE TO BE
FASTER THAN THE OFFICIAL FORECAST...AND IF HANNA DEVELOPS FASTER
THAN SHOWN BELOW ADDITIONAL TIMING ADJUSTMENTS MAY NEED TO BE MADE.
IT'S WORTH NOTING THAT CONNECTING THE 48 AND 72 HOUR FORECAST POINTS
WITH A STRAIGHT LINE GIVES A MISLEADING UNDERESTIMATE OF THE
THREAT TO THE GEORGIA AND SOUTH CAROLINA COASTS.  ONLY A GRADUAL
RIGHT TURN IS EXPECTED AFTER 48 HOURS.

AS THE UPPER LOW IN THE BAHAMAS AND HANNA SEPARATE...THE SOUTHERLY
SHEAR OVER THE CYCLONE WILL TURN SOUTHEASTERLY AND LESSEN.  THIS IS
EXPECTED TO PROVIDE A MORE FAVORABLE ENVIRONMENT FOR
STRENGTHENING...ALTHOUGH NONE OF THE OBJECTIVE AIDS SHOWS VERY
MUCH.  THE SHIPS AND LGEM BRING THE SYSTEM ONLY TO 60 KT...AND THE
HWRF NOT QUITE THAT HIGH.  THE OFFICIAL FORECAST IS IN GOOD
AGREEMENT WITH THE GFDL WHICH BRINGS HANNA TO 70 KT PRIOR TO
LANDFALL.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      03/2100Z 21.9N  71.9W    50 KT
 12HR VT     04/0600Z 23.2N  72.7W    55 KT
 24HR VT     04/1800Z 25.2N  74.5W    60 KT
 36HR VT     05/0600Z 27.4N  76.6W    65 KT
 48HR VT     05/1800Z 30.0N  78.5W    70 KT
 72HR VT     06/1800Z 36.8N  76.9W    50 KT...INLAND
 96HR VT     07/1800Z 44.5N  67.0W    35 KT...EXTRATROPICAL
120HR VT     08/1800Z 48.0N  55.0W    35 KT...EXTRATROPICAL
 
$$
FORECASTER FRANKLIN
 
NNNN


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Page last modified: Tuesday, 21-Apr-2009 12:09:17 UTC