[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 310853
TCDAT3
TROPICAL STORM FIONA DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
500 AM AST TUE AUG 31 2010

FIONA HAS CHANGED LITTLE IN STRUCTURE DURING THE LAST SEVERAL HOURS.
DEEP CONVECTION REMAINS CONFINED TO A FEW CURVED BANDS MAINLY OVER
THE WESTERN SEMICIRCLE...ALTHOUGH AN AREA OF THUNDERSTORMS HAS
RECENTLY FORMED NEAR THE ESTIMATED CENTER POSITION. THE INITIAL
INTENSITY IS HELD AT 35 KT...IN AGREEMENT WITH AN 0056 UTC ASCAT
PASS AND A 1007 MB PRESSURE REPORT FROM BUOY 41040. ONLY A LITTLE
STRENGTHENING IS FORECAST IN THE SHORT TERM DUE TO MARGINALLY
FAVORABLE UPPER-LEVEL WINDS...SOME DRY AIR AROUND THE CYCLONE...AND
CURRENT LACK OF ORGANIZATION. THE SHIPS MODEL SHOWS NORTHEASTERLY
SHEAR INCREASING SIGNIFICANTLY IN 24-36 HOURS...AND IF
CORRECT...THAT SHOULD LIMIT ADDITIONAL STRENGTHENING. THIS
INTENSITY FORECAST IS UNCHANGED FROM EARLIER AND REMAINS NEAR THE
LOW END OF THE MODEL GUIDANCE.

THE AFOREMENTIONED ASCAT PASS AND A TRMM OVERPASS AT 0303 UTC
SUGGESTED THAT THE LOW-LEVEL CENTER...ALBEIT NOT VERY EASY TO
LOCATE...WAS SITUATED A LITTLE TO THE NORTH OF THE PREVIOUS
ESTIMATES. THEREFORE...THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN
285/20. A NARROW MID-LEVEL RIDGE LOCATED ALONG 25 N OVER THE
CENTRAL AND EASTERN ATLANTIC IS EXPECTED TO KEEP FIONA ON A RATHER
FAST WEST-NORTHWESTWARD COURSE FOR THE NEXT DAY OR SO.
THEREAFTER...THE CYCLONE IS EXPECTED TO APPROACH A WEAKNESS IN THE
RIDGE...WHICH WILL BE ENHANCED BY HURRICANE EARL...AND THAT SHOULD
CAUSE FIONA TO GRADUALLY SLOW DOWN AND TURN TO THE NORTHWEST. THE
ECMWF...WHICH HAS BEEN THE LEFT-MOST MODEL FOR THE PAST COUPLE OF
CYCLES...IS NOW ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE. IN
GENERAL...THE MODEL GUIDANCE HAS SHIFTED SLIGHTLY TO THE RIGHT AND
IS A LITTLE FASTER AT THE END OF THE PERIOD...AND THE NHC FORECAST
HAS BEEN ADJUSTED IN THAT DIRECTION.

FORECAST POSITIONS AND MAX WINDS

INITIAL      31/0900Z 15.8N  53.0W    35 KT
 12HR VT     31/1800Z 16.5N  55.7W    35 KT
 24HR VT     01/0600Z 17.8N  59.1W    40 KT
 36HR VT     01/1800Z 19.6N  61.9W    45 KT
 48HR VT     02/0600Z 21.8N  64.2W    45 KT
 72HR VT     03/0600Z 26.5N  67.5W    45 KT
 96HR VT     04/0600Z 29.0N  68.5W    45 KT
120HR VT     05/0600Z 30.5N  69.0W    45 KT

$$
FORECASTER CANGIALOSI/BLAKE



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