Subtropical Storm LAURA

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SUBTROPICAL STORM LAURA DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122008
500 AM EDT TUE SEP 30 2008
 
LAURA CONTINUES TO PRODUCE CONVECTIVE BANDS AROUND THE CENTER...WITH
CLOUD TOPS COLDER THAN -60C TO THE NORTH AND NORTHEAST OF THE
CENTER.  A RECENT AMSU OVERPASS SHOWS A WELL-DEFINED MID/UPPER-
LEVEL WARM CORE...SUGGESTING THAT LAURA IS BECOMING MORE TROPICAL. 
HOWEVER...WATER VAPOR IMAGERY SHOWS THAT THE SYSTEM IS STILL
STRONGLY INVOLVED WITH AN UPPER-LEVEL LOW.  ALSO...THERE ARE NO
SIGNS OF THE ANTICYCLONIC UPPER-LEVEL OUTFLOW CHARACTERISTIC OF A
TROPICAL CYCLONE.  BASED ON THIS...THE SYSTEM IS STILL DESIGNATED A
SUBTROPICAL STORM.  SATELLITE INTENSITY ESTIMATES ARE UNCHANGED
SINCE 6 HR AGO...SO THE INITIAL INTENSITY REMAINS 50 KT.  

LAURA HAS JOGGED TO THE LEFT AND ACCELERATED OVER THE PAST FEW
HOURS...WITH THE INITIAL MOTION NOW 350/11.  OTHER THAN THAT...
THERE IS LITTLE CHANGE IN THE FORECAST PHILOSOPHY FROM THE
PREVIOUS ADVISORY.  A DEEP-LAYER RIDGE OVER THE NORTHEASTERN
ATLANTIC AND A MID/UPPER-LEVEL TROUGH MOVING EASTWARD THROUGH NEW
ENGLAND AND THE CANADIAN MARITIMES SHOULD STEER LAURA GENERALLY
NORTH-NORTHEASTWARD FOR THE NEXT 48 HR OR SO...FOLLOWED BY A SHARP
RIGHT TURN AS THE CYCLONE ENTERS THE WESTERLIES.  WHILE THERE IS
THE NORMAL AMOUNT OF SPREAD IN THE GUIDANCE...IT ALL AGREES WITH
THIS SCENARIO.  THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS
ADVISORY...BUT NUDGED A LITTLE TO THE LEFT BASED ON THE CURRENT
POSITION AND MOTION.

LAURA WILL BE MOVING OVER STEADILY DECREASING SEA SURFACE
TEMPERATURES DURING THE NEXT 36-48 HR...WITH THE SYSTEM LIKELY TO
ENCOUNTER SSTS OF 12C BY 36 HR.  THIS SUGGESTS THE SYSTEM SHOULD
GRADUALLY WEAKEN AS THE FALLING SSTS CAUSE THE CONVECTION TO
DECREASE.  THE SYSTEM IS EXPECTED TO UNDERGO EXTRATROPICAL
TRANSITION BETWEEN 24-48 HR...AND AFTER THIS IS COMPLETE THE
LARGE-SCALE MODELS FORECAST SOME RE-INTENSIFICATION AS A BAROCLINIC
LOW.  IT SHOULD BE NOTED THAT NONE OF THE LARGE-SCALE MODELS
CURRENTLY FORECAST LAURA TO PRODUCE STORM-FORCE...50 KT...WINDS AS
AN EXTRATROPICAL LOW.  BASED ON THIS...THE 120 HR FORECAST
INTENSITY IS NUDGED DOWNWARD...AND ADDITIONAL ADJUSTMENTS TO THE
FORECAST INTENSITY MAY BE NECESSARY IF THE CURRENT MODEL INTENSITY
FORECASTS PERSIST.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/0900Z 40.3N  49.0W    50 KT
 12HR VT     30/1800Z 42.0N  48.5W    50 KT
 24HR VT     01/0600Z 44.6N  47.7W    50 KT
 36HR VT     01/1800Z 47.5N  46.5W    45 KT...EXTRATROPICAL
 48HR VT     02/0600Z 50.6N  44.5W    40 KT...EXTRATROPICAL
 72HR VT     03/0600Z 55.0N  37.0W    45 KT...EXTRATROPICAL
 96HR VT     04/0600Z 56.0N  25.0W    50 KT...EXTRATROPICAL
120HR VT     05/0600Z 56.0N  10.0W    50 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN
 
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