Subtropical Storm LAURA

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SUBTROPICAL STORM LAURA DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122008
500 PM EDT MON SEP 29 2008
 
AN ASCAT PASS AROUND 1326 UTC THIS MORNING INDICATED MAXIMUM WINDS
NEAR 45 KT...BUT THIS SENSOR USUALLY TENDS TO HAVE A SLIGHT LOW
BIAS SO AN INTENSITY OF 50 KT WILL BE MAINTAINED IN THIS PACKAGE. 
LAURA CONTINUES TO ACQUIRE SOME TROPICAL CHARACTERISTICS...WITH THE
FSU PHASE SPACE DIAGRAMS AND AMSU DATA BOTH INDICATING A DEEP WARM
CORE.  ON THE OTHER HAND...THE ASSOCIATED CONVECTION IS NOT ALL
THAT DEEP AND THE 75 NM RADIUS OF MAXIMUM WINDS IS IN THE GRAY ZONE
BETWEEN TROPICAL AND SUBTROPICAL.  LAURA WILL CONTINUE TO BE
CLASSIFIED AS A SUBTROPICAL STORM FOR NOW ALTHOUGH THE TRANSITION
TO A TROPICAL CYCLONE IS LIKELY OCCURRING.

LATEST SATELLITE FIXES INDICATE THAT LAURA IS TURNING AND
ACCELERATING WITH AN INITIAL MOTION OF 335/8.  THE TRACK FORECAST
REASONING HAS NOT CHANGED.  ALTHOUGH SOME OF THE MODELS...INCLUDING
THE GFS...GFDL...AND ECMWF...HAVE SHIFTED LEFT SINCE THIS
MORNING...THE OFFICIAL FORECAST LIES VERY CLOSE TO THE MODEL
CONSENSUS AND IS NOT FAR FROM THE PREVIOUS FORECAST.

IF LAURA IS BECOMING MORE TROPICAL...IT HAS A CHANCE TO STRENGTHEN A
LITTLE BEFORE IT MOVES OVER COLDER WATERS. THE OFFICIAL FORECAST
FOLLOWS CLOSE TO THE SHIPS AND LGEM MODELS FOR THE FIRST 36 HOURS
BUT THEN CALLS FOR GRADUAL WEAKENING ONCE LAURA BECOMES
EXTRATROPICAL AND MOVES INTO A COLDER AIR MASS...MUCH LIKE AN
OCCLUDED LOW. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE
GFDL AND HWRF GUIDANCE. LAURA WILL BEGIN EXTRATROPICAL TRANSITION
BY 36 HOURS AND THEN COULD BE FULLY ABSORBED INTO A FRONTAL ZONE BY
DAY 5 WEST OF IRELAND...ALTHOUGH A POINT AT THAT TIME IS STILL
GIVEN FOR CONTINUITY.


FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/2100Z 38.3N  48.4W    50 KT
 12HR VT     30/0600Z 39.3N  48.6W    55 KT
 24HR VT     30/1800Z 41.2N  48.3W    60 KT
 36HR VT     01/0600Z 43.6N  47.4W    55 KT
 48HR VT     01/1800Z 46.5N  46.0W    50 KT...EXTRATROPICAL
 72HR VT     02/1800Z 52.5N  41.0W    50 KT...EXTRATROPICAL
 96HR VT     03/1800Z 55.0N  28.0W    45 KT...EXTRATROPICAL
120HR VT     04/1800Z 55.0N  12.0W    45 KT...EXTRATROPICAL
 
$$
FORECASTER BERG/FRANKLIN
 
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