[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 171440
TCDAT3

TROPICAL STORM GORDON DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL082012
1100 AM AST FRI AUG 17 2012

THE SATELLITE APPEARANCE OF GORDON REMAINS RATHER UNIMPRESSIVE...
WITH CLOUD TOP TEMPERATURES WARMING OVER THE PAST FEW HOURS AND THE
COLDEST CLOUD TOPS DISPLACED NORTH AND WEST OF THE CENTER. UW-CIMSS
SATELLITE ANALYSIS AND SHIPS DIAGNOSTICS SHOW AROUND 15 KT OF
WEST-NORTHWESTERLY SHEAR OVER THE CYCLONE...WHILE MET-9 AIRMASS
IMAGERY AND MICROWAVE IMAGERY SHOW SOME DRY AIR WRAPPING INTO THE
CIRCULATION FROM THE SOUTHWEST. THE INITIAL INTENSITY IS HELD AT 55
KT BASED ON A BLEND OF THE LATEST DVORAK FINAL-T AND CI-NUMBERS
FROM TAFB AND SAB. THE CENTRAL PRESSURE OF 997 MB IS BASED ON AN
OBSERVATION OF 999 MB FROM A DRIFTING BUOY THAT THE CENTER PASSED
JUST NORTH OF AROUND 1000 UTC.

THE SHEAR IS FORECAST TO DECREASE A LITTLE IN THE SHORT TERM...WHICH
SHOULD ALLOW GORDON TO STRENGTHEN A BIT BEFORE THE CYCLONE REACHES
SUB-26C WATERS AND THE SHEAR INCREASES IN 36 TO 48 HOURS. THE NHC
FORECAST SHOWS THE CYCLONE PEAKING AT 60 KT IN 24 TO 36 HOURS AND
IS CLOSE TO A BLEND OF THE SHIPS AND LGEM MODELS UNTIL
EXTRATROPICAL TRANSITION OCCURS.

THE INITIAL MOTION ESTIMATE IS A LITTLE SOUTH OF DUE EAST...095/16.
GORDON WILL BE STEERED GENERALLY EASTWARD FOR THE NEXT DAY OR SO TO
THE SOUTH OF A LARGE MID/UPPER-LEVEL TROUGH OVER THE NORTHEASTERN
ATLANTIC. BY 48 HOURS...A SHORTWAVE TROUGH IS EXPECTED TO APPROACH
THE CYCLONE FROM THE WEST AND INDUCE AN EAST-NORTHEASTWARD TURN AS
THE CYCLONE BECOMES EXTRATROPICAL IN ABOUT 3 DAYS. A SLOW EAST-
NORTHEASTWARD MOTION IS EXPECTED AT DAYS 4 AND 5 AS THE CYCLONE
WEAKENS. OVERALL THE TRACK MODEL GUIDANCE REMAINS IN GOOD AGREEMENT
ON THIS SCENARIO. THE NEW NHC FORECAST IS LARGELY AN UPDATE OF THE
PREVIOUS ONE AND IS CLOSE TO A CONSENSUS OF THE GFS AND ECMWF.

THE 34-KT WIND RADII WERE ADJUSTED OUTWARD BASED ON A PARTIAL ASCAT
PASS FROM AROUND 1250 UTC.

FORECAST POSITIONS AND MAX WINDS

INIT  17/1500Z 34.5N  46.3W   55 KT  65 MPH
 12H  18/0000Z 34.2N  43.4W   55 KT  65 MPH
 24H  18/1200Z 34.1N  39.6W   60 KT  70 MPH
 36H  19/0000Z 34.4N  35.6W   60 KT  70 MPH
 48H  19/1200Z 35.2N  31.8W   55 KT  65 MPH
 72H  20/1200Z 38.0N  24.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  21/1200Z 39.0N  19.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  22/1200Z 39.5N  16.5W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BRENNAN



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