[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 120244
TCDAT4

TROPICAL STORM MARIA DISCUSSION NUMBER  22
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142011
1100 PM AST SUN SEP 11 2011

WITHOUT RECON DATA OR VISIBLE SATELLITE IMAGERY...THE LOCATION OF
THE CENTER OF MARIA HAS BEEN A STRUGGLE TO PINPOINT. RADAR DATA
FROM SAN JUAN WERE INCONCLUSIVE...BUT A COUPLE OF MICROWAVE
PASSES...CONTINUITY FROM THE PREVIOUS TRACK...AND LAST-VISIBLE
SATELLITE IMAGES SUGGEST THAT THE CENTER OF MARIA REMAINS TO THE
WEST OF A LARGE BLOB OF VERY COLD-TOPPED CONVECTION. OBSERVATIONS
FROM THE NEARBY NOAA BUOY 41043 AND OTHER SURFACE SYNOPTIC DATA
SUGGEST AN EAST-WEST ELONGATION TO THE LOW-LEVEL CENTER. DVORAK
T-NUMBERS ARE 3.0 AND 3.5 FROM SAB AND TAFB AND...WITH NO APPARENT
CHANGE IN THE STORM STRUCTURE SINCE THE LAST ADVISORY...THE INITIAL
INTENSITY IS KEPT AT 50 KT.

ALTHOUGH UNCERTAIN...RECENT FIXES YIELD A MOTION OF 300/09...MORE OR
LESS. MODEL GUIDANCE SHOWS MARIA APPROACHING THE WESTERN EXTENSION
OF A LOW- TO MID-LEVEL RIDGE DURING THE NEXT 36 HOURS...A SYNOPTIC
PATTERN THAT SHOULD FAVOR A SLOW WEST-NORTHWESTWARD TO
NORTHWESTWARD MOTION.  BETWEEN 36-72 HOURS...A TROUGH IN THE
SOUTHERN STREAM OVER THE SOUTHEASTERN UNITED STATES IS FORECAST TO
SLIDE EASTWARD...GRADUALLY INDUCING A RECURVING TRACK NEAR 70W.
A LARGER AND MORE POTENT TROUGH SWINGING THROUGH THE NORTHEASTERN
STATES BY 96 HOURS SHOULD ACCELERATE MARIA NORTHEASTWARD OVER
HIGHER LATITUDES.  THE OFFICIAL NHC TRACK IS LARGELY UNCHANGED FROM
THE PREVIOUS ONE THROUGH 36 HOURS...AND A HAIR TO THE LEFT AFTER
THAT FOLLOWING THE MULTI-MODEL CONSENSUS.

AS ALWAYS...THE INTENSITY FORECAST IS FAIRLY CHALLENGING.  UW-CIMSS
AND SHIPS SHEAR ANALYSES INDICATE MODERATE TO STRONG WESTERLY SHEAR
PREVAILING OVER MARIA AS A RESULT OF A SHARP UPPER TROUGH JUST
NORTHWEST OF THE CYCLONE.  LARGE-SCALE MODELS SHOW LITTLE TO NO
DECREASE IN THE SHEAR FOR AT LEAST 36 HOURS...WHICH MAKES THE
PROSPECTS FOR SIGNIFICANT SHORT-TERM INTENSIFICATION SLIM.  BETWEEN
36-72 HOURS...THERE COULD BE A MODEST REDUCTION IN THE SHEAR AS THE
INFLUENCE OF THE NEARBY UPPER-LEVEL TROUGH WEAKENS. HOWEVER...MARIA
IS FORECAST TO MOVE OVER OR CLOSE TO THE COLD WAKE LEFT BEHIND BY
KATIA WHICH TRAVERSED THIS REGION LESS THAN A WEEK AGO.  IN SPITE OF
THE GENERALLY UNFAVORABLE CONDITIONS...THE REGIONAL HURRICANE
MODELS SHOW SIGNIFICANT STRENGTHENING AROUND 48 HOURS.  THE
OFFICIAL INTENSITY FORECAST IS MORE CONSERVATIVE AND FOLLOWS THE
STATISTICAL-DYNAMICAL LGEM GUIDANCE.  BEYOND 72 HOURS...A SHARP
INCREASE IN SOUTHWESTERLY SHEAR IS FORECAST IN ASSOCIATION WITH THE
TROUGH OVER THE WESTERN ATLANTIC...WHICH SHOULD BRING ANY
STRENGTHENING TO AN END.  GIVEN THE ENORMOUS VERTICAL SHEAR
INDICATED BY THE GLOBAL MODELS BY 96-120 HOURS...EXTRATROPICAL
TRANSITION SEEMS LIKELY BY THE END OF THE FORECAST PERIOD.

FORECAST POSITIONS AND MAX WINDS

INIT  12/0300Z 20.2N  65.9W   50 KT  60 MPH
 12H  12/1200Z 21.1N  67.0W   50 KT  60 MPH
 24H  13/0000Z 22.5N  68.2W   50 KT  60 MPH
 36H  13/1200Z 23.7N  69.2W   50 KT  60 MPH
 48H  14/0000Z 25.5N  69.5W   55 KT  65 MPH
 72H  15/0000Z 31.5N  68.2W   65 KT  75 MPH
 96H  16/0000Z 40.7N  61.5W   60 KT  70 MPH
120H  17/0000Z 50.0N  48.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
FORECASTER KIMBERLAIN



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