[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 130859
TCDAT4

TROPICAL STORM MARIA DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142011
500 AM AST TUE SEP 13 2011

THE OVERALL CONVECTIVE ORGANIZATION OF MARIA HAS CHANGED LITTLE
OVERNIGHT. NORTHWESTERLY VERTICAL WIND SHEAR AND DRY AIR INTRUSIONS
INTO THE WESTERN SEMICIRCLE OF THE CYCLONE CONTINUE TO INHIBIT THE
DEVELOPMENT PROCESS. UPPER-LEVEL OUTFLOW IS EXCELLENT IN THE
EASTERN SEMICIRCLE...BUT IS RESTRICTED TO THE NORTHWEST...ALBEIT
HAVING IMPROVED SLIGHTLY DURING THE PAST FEW HOURS. THE INITIAL
INTENSITY REMAINS AT 45 KT BASED ON SATELLITE INTENSITY ESTIMATES
OF 45 KT FROM TAFB AND SAB.

NIGHTTIME VISIBLE IMAGERY PLUS A 0520Z TRMM MICROWAVE OVERPASS
INDICATE MULTIPLE SMALL CIRCULATIONS ROTATING AROUND THE CENTER OF
A LARGER LOW-LEVEL CYCLONIC GYRE. AS A RESULT...THE INITIAL
POSITION IS THE MEAN CENTER OF THE LARGER CYCLONIC ENVELOPE...WHICH
MAKES THE INITIAL MOTION OF 330/04 KT SOMEWHAT UNCERTAIN. THE
NORTHWESTERLY TO WESTERLY VERTICAL SHEAR IS EXPECTED TO CONTINUE
FOR THE NEXT 24 HOURS OR SO...WHICH SHOULD KEEP THE DEEP CONVECTION
AND THE VERTICAL CIRCULATION OF MARIA DISPLACED TO THE EAST OF MOST
OF THE MODEL GUIDANCE. BY 36 HOURS...MARIA IS EXPECTED TO GET
CAUGHT UP IN INCREASING SOUTHWESTERLY FLOW AHEAD OF A DEEP-LAYER
TROUGH THAT IS CURRENTLY PASSING THE SOUTHERN TIP OF FLORIDA AS
NOTED IN WATER VAPOR IMAGERY. THE CYCLONE SHOULD GRADUALLY
ACCELERATE TO THE NORTHEAST...AND BY 96 HOURS BEGIN TO MERGE WITH A
LARGER EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE CANADIAN
MARITIMES REGION. THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE
RIGHT OF THE PREVIOUS ADVISORY TRACK...AND LIES ALONG THE EASTERN
EDGE OF THE GUIDANCE ENVELOPE AND FOLLOWS THE SPEED OF THE
CONSENSUS MODEL TVCN.

MARIA IS EXPECTED TO REMAIN UNDER UNFAVORABLE WESTERLY SHEAR
CONDITIONS FOR THE NEXT 24 HOURS OR SO. HOWEVER...BY 36 HOURS...
THE UPPER-LEVEL LOW JUST TO THE NORTH OF THE MARIA...THAT HAS BEEN
CREATING CONDITIONS QUITE HOSTILE FOR INTENSIFICATION TO OCCUR...IS
EXPECTED TO DISSIPATE. THE RESULT IS THAT THE VERTICAL SHEAR IS
FORECAST TO DECREASE BELOW 10 KT AND FOR THE SHEAR DIRECTION TO
BACK AROUND TO THE SOUTH-SOUTHWEST. THIS SHOULD ALLOW FOR AT LEAST
SOME MODEST STRENGTHENING TO OCCUR UNTIL THE VERTICAL SHEAR
INCREASES FROM THE SOUTHWEST BY AROUND 48 HOURS. AT 72 HOURS AND
BEYOND...MARIA WILL BE MOVING OVER SSTS COLDER THAN 20C...WHICH
SHOULD INDUCE EXTRATROPICAL TRANSITION AND GRADUAL WEAKENING. THE
INTENSITY FORECAST IS A BLEND OF THE SHIPS AND LGEM INTENSITY
MODELS...AND REMAINS WELL BELOW THE INTENSITY FORECASTS OF THE
GLOBAL AND REGIONAL MODELS...WHICH ARE ALL FORECASTING MARIA TO
BECOME A HURRICANE IN 48-72 HOURS.

FORECAST POSITIONS AND MAX WINDS

INIT  13/0900Z 21.6N  67.7W   45 KT  50 MPH
 12H  13/1800Z 22.8N  68.3W   45 KT  50 MPH
 24H  14/0600Z 24.8N  68.7W   50 KT  60 MPH
 36H  14/1800Z 27.5N  68.7W   55 KT  65 MPH
 48H  15/0600Z 31.2N  67.9W   55 KT  65 MPH
 72H  16/0600Z 39.8N  61.0W   50 KT  60 MPH
 96H  17/0600Z 51.0N  45.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  18/0600Z...DISSIPATED/ABSORBED

$$
FORECASTER STEWART

WWWW
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