[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 112039
TCDAT4

TROPICAL STORM MARIA DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142011
500 PM AST SUN SEP 11 2011

MARIA REMAINS A SHEARED TROPICAL CYCLONE.  SEVERAL LOW-LEVEL CLOUD
SWIRLS HAVE BEEN SEEN ROTATING AROUND THE EXPOSED MEAN CIRCULATION
CENTER.  POSITION ESTIMATES FROM THE UNITED STATES AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT WERE A BIT SCATTERED AS THEY FIXED THE
DIFFERENT SWIRLS DURING THE FLIGHT.  THE AIRCRAFT REPORTED PEAK 850
MB FLIGHT-LEVEL WINDS OF 53 KT AND BELIEVABLE SFMR WINDS OF 45-48
KT...WHICH SUPPORT AN INITIAL INTENSITY OF 50 KT.  THE UPPER-LEVEL
WIND PATTERN IS PREDICTED TO REMAIN HOSTILE BY THE GLOBAL MODELS
DURING THE NEXT 24-36 HOURS.  HOWEVER...THE UPPER-LEVEL WINDS COULD
BECOME A LITTLE MORE CONDUCIVE IN 2-3 DAYS AS AN UPPER-LEVEL RIDGE
IS FORECAST TO BUILD NORTHEAST OF THE BAHAMAS.  THIS WINDOW OF
OPPORTUNITY FOR STRENGTHENING APPEARS AS THOUGH IT WILL BE
SHORT...AS STRONG SOUTHWESTERLY SHEAR ASSOCIATED A MID-LATITUDE
TROUGH IMPINGES ON THE CYCLONE BY 96 HOURS.  AFTER THAT...MARIA IS
FORECAST TO INTERACT WITH A FRONTAL BOUNDARY AND BECOME AN
EXTRATROPICAL CYCLONE BY 120 HOURS.

THE CENTROID OF THE LARGER CIRCULATION IS LOCATED A LITTLE NORTH OF
THE PREVIOUS ADVISORY ESTIMATE...WHICH REQUIRED A SLIGHT RELOCATION.
SMOOTHING THROUGH THE FIXES DURING THE PAST 12 HOURS OR SO YIELDS AN
INITIAL MOTION ESTIMATE OF 300/9 KT.  MARIA SHOULD MOVE WEST-
NORTHWESTWARD TO NORTHWESTWARD DURING THE NEXT DAY OR SO... THEN
TURN NORTHWARD AHEAD OF A TROUGH APPROACHING THE EAST COAST OF THE
UNITED STATES.  MARIA SHOULD RECURVE NORTHEASTWARD AHEAD OF A
SECOND TROUGH MOVING THROUGH THE GREAT LAKES AND NORTHEAST UNITED
STATES DURING THE 3-5 DAY TIME PERIOD.  THE TRACK GUIDANCE HAS COME
INTO BETTER AGREEMENT THIS CYCLE WITH THE ECMWF SHIFTING
EASTWARD...AND CLOSER TO THE GFS TRACK.  THE NEW NHC TRACK IS
ESSENTIALLY AN UPDATE OF THE PREVIOUS ADVISORY.

ALTHOUGH THE STRONGEST WINDS WILL REMAIN OVER WATER TO THE NORTH
OF THE NORTHERN CARIBBEAN ISLANDS...WIND GUSTS TO TROPICAL STORM
FORCE ARE POSSIBLE IN THE RAIN BANDS CURRENTLY OVER THE LEEWARD
ISLANDS.  THESE SHOWERS AND THUNDERSTORMS ARE EXPECTED TO SPREAD
OVER THE VIRGIN ISLANDS AND PUERTO RICO TONIGHT AND MONDAY.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 19.8N  65.2W   50 KT  60 MPH
 12H  12/0600Z 20.6N  66.3W   50 KT  60 MPH
 24H  12/1800Z 21.7N  67.6W   50 KT  60 MPH
 36H  13/0600Z 22.8N  68.7W   50 KT  60 MPH
 48H  13/1800Z 24.2N  69.4W   55 KT  65 MPH
 72H  14/1800Z 29.3N  69.2W   65 KT  75 MPH
 96H  15/1800Z 37.5N  64.5W   65 KT  75 MPH
120H  16/1800Z 49.5N  51.5W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BROWN

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