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SUBTROPICAL STORM TWO DISCUSSION NUMBER 3
NATIONAL WEATHER SERVICE MIAMI FL
4 AM EST SUN NOV 25 2001
SUBTROPICAL STORM TWO IS BEGINNING TO LOOK MORE TROPICAL AND LESS
EXTRATROPICAL IN SATELLITE IMAGERY. THE INNER-CORE CONVECTION NEAR
THE LOW-LEVEL CENTER HAS BECOME DETACHED FROM THE MAIN CLOUD SHIELD
DURING THE PAST FEW HOURS. IN ADDITION...TWO INTERLOCKING BANDS OF
CONVECTION HAVE BECOME MORE DISTINCT AROUND THE CENTER. OUTFLOW IS
FAIR TO THE NORTH AND WEAK TO THE SOUTH. THE INITIAL INTENSITY OF 50
KT IS BASED ON A BLEND OF DVORAK SATELLITE INTENSITY ESTIMATES OF 50
KT...45 KT...AND 55 KT FROM TAFB...SAB...AND AFWA...RESPECTIVELY.
THE INITIAL MOTION ESTIMATE IS 295/14. SUBTROPICAL STORM TWO HAS
ACCELERATED MORE WESTWARD DURING THE PAST 6 HOURS IN RESPONSE TO THE
LARGE SURFACE HIGH AND MID-LEVEL RIDGE THAT HAVE STARTED BUILDING
EASTWARD TO THE NORTH OF THE CYCLONE. WATER VAPOR IMAGERY INDICATES
THE POWERFUL MID-LATITUDE LOW OVER THE U.S. GREAT LAKES REGION
LIFTING OUT TO THE NORTHEAST...WHICH IS ACTING TO THE AMPLIFY THE
DOWNSTREAM RIDGING OFF THE U.S. EAST COAST. THIS BLOCKING PATTERN IS
EXPECTED TO PERSIST THROUGHOUT THE FORECAST PERIOD...WHICH SHOULD
ACT TO KEEP THE STORM MOVING IN A GENERAL WESTWARD DIRECTION. ALMOST
ALL OF THE NHC MODEL GUIDANCE AGREE ON A WEST-NORTHWEST OR WESTWARD
TRACK...WITH A SIGNIFICANT DECREASE IN FORWARD SPEED BY 36 TO 48
HOURS. IT IS POSSIBLE THAT THE CYCLONE COULD EVEN STALL DURING THAT
TIME PERIOD AND MOVE ERRATICALLY. HOWEVER...ALL OF THE AVAILABLE
GUIDANCE AGREE ON KEEPING THE STORM SYSTEM WELL TO THE EAST OF
BERMUDA THROUGH 72 HOURS. THE OFFICIAL FORECAST IS SLIGHTLY SOUTH
OR TO THE LEFT OF THE PREVIOUS FORECAST TRACK AND IS CLOSE TO THE
AVN-GFDL-UKMET MODEL CONSENSUS.
BASED ON THE IMPROVING SATELLITE SIGNATURE...IT IS ENTIRELY POSSIBLE
THAT SUBTROPICAL STORM TWO COULD TRANSITION OVER COMPLETELY TO A
TROPICAL CYCLONE LATER TODAY. ALL OF THE GLOBAL MODELS AGREE THAT
THE UPPER-LEVEL SHEAR WILL WEAKEN THROUGHOUT THE FORECAST PERIOD.
IN FACT...BY 48 HOURS...THE AVN MODEL DECREASES THE SHEAR TO LESS
THAN 10 KT. AS SUCH...SLOW STRENGTHENING IS FORECAST THROUGH 36
HOURS...EVEN THOUGH SEA-SURFACE TEMPERATURES ARE COOLER THAN 24C.
HOWEVER...THE UNSUALLY COLD MID- AND UPPER-LEVEL ENVIRONMENT IS
PROVIDING THE NECESSARY INSTABILITY FOR THUNDERSTORM DEVELOPMENT TO
OCCUR. THE NEW FORECAST TRACK ACTUALLY TAKES THE CYCLONE OVER
WARMER SSTS...SO SOME STRENGTHENING APPEARS TO BE IN ORDER. GIVEN
THE FAVORABLE UPPER-LEVEL WINDS FORECAST...THIS SYSTEM COULD EVEN
REACH HURRICANE INTENSITY.
THE WIND RADII WERE DECREASED AFTER 36 HOURS TO REFLECT THE EXPECTED
SHRINKING OF THE OUTER WIND FIELD OWING TO THE WEAKENING SURFACE
HIGH TO THE NORTH...AND CONTRACTION OF THE INNER-CORE WIND FIELD
WHEN THE SYSTEM BECOMES MORE TROPICAL-LIKE.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 25/0900Z 32.0N 52.3W 50 KTS
12HR VT 25/1800Z 32.3N 53.5W 55 KTS
24HR VT 26/0600Z 32.5N 54.7W 55 KTS
36HR VT 26/1800Z 32.5N 55.7W 60 KTS
48HR VT 27/0600Z 32.4N 56.7W 60 KTS
72HR VT 28/0600Z 32.2N 58.0W 60 KTS
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