[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 030855
TCDAT1

TROPICAL STORM OPHELIA DISCUSSION NUMBER  43
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
500 AM AST MON OCT 03 2011

THE SATELLITE PRESENTATION OF OPHELIA HAS CONTINUED TO DETERIORATE
THIS MORNING...AND THE CYCLONE IS QUICKLY LOSING ITS TROPICAL
CHARACTERISTICS OVER WATER TEMPERATURES BETWEEN 10-15 CELSIUS.
THERE REMAINS A SMALL AREA OF MODERATE CONVECTION WITH CLOUD TOPS
COLDER THAN -50C JUST NORTHEAST OF THE ALLEGED CENTER...BUT THE
AREAL COVERAGE OF THIS CONVECTION HAS BEEN RAPIDLY SHRINKING.
HOWEVER...A 03/0556Z AMSU OVERPASS STILL INDICATED A VERTICALLY
STACKED WARM CORE THROUGH AT LEAST THE 250/200 MB LEVEL...AND THAT
IS THE JUSTIFICATION FOR MAINTAINING OPHELIA AS A TROPICAL CYCLONE
ON THIS ADVISORY.

THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 055/37 KT...BASED ON
EXTRAPOLATION...CONVENTIONAL SATELLITE FIXES...AND A 03/0621 AMSR-E
MICROWAVE OVERPASS. OPHELIA IS EXPECTED TO MOVE NORTHEASTWARD THIS
MORNING AND MAKE LANDFALL ALONG THE AVALON PENINSULA BETWEEN
ROUGHLY 10-12Z THIS MORNING. VERY COLD WATER BENEATH OPHELIA AND
INCREASING VERTICAL WIND SHEAR IN EXCESS OF 40 KT SHOULD RESULT IN
COMPLETE TRANSITION TO AN EXTRATROPICAL LOW PRESSURE SYSTEM BY
18Z...IF NOT SOONER. THE OFFICIAL TRACK FORECAST IS DOWN THE MIDDLE
OF THE TIGHTLY PACKED NHC MODEL GUIDANCE SUITE...AND LIES CLOSE TO
THE GUIDANCE PROVIDED BY THE NOAA OCEAN PREDICTION CENTER.

A 03/0027Z ASCAT OVERPASS INDICATED A LARGE SWATH OF 50-55 KT WIND
VECTORS IN THE EAST AND SOUTHEAST OCTANTS OF THE CIRCULATION. GIVEN
THE KNOWN LOW BIAS OF THIS REMOTE SENSING INSTRUMENT...OPHELIA WAS
KEPT AS A 65-KT HURRICANE AT 06Z...AND IS NOW A 60-KT TROPICAL
STORM DUE TO THE LOSS OF CENTRAL DEEP CONVECTION IN THE REGION OF
STRONGEST WINDS NOTED IN THE ASCAT DATA. CANADIAN RADAR DATA FROM
THE AVALON PENINSULA INDICATE THE RAIN SHIELD AHEAD OF THE CENTER
IS MOSTLY STRATIFORM IN NATURE...FURTHER INDICATING THAT OPHELIA IS
UNDERGOING EXTRATROPICAL TRANSITION. OPHELIA SHOULD CONTINUE TO
WEAKEN OVER COLDER WATER AND EVENTUALLY MERGE WITH A FRONTAL SYSTEM
IN 24-36 HOURS. THE OFFICIAL INTENSITY FORECAST AND FORECAST WIND
RADII ARE BASED ON GUIDANCE PROVIDED BY THE NOAA OCEAN PREDICTION
CENTER.

ADVISORY WIND RADII WERE ADJUSTED BASED ON A 03/0027Z ASCAT OVERPASS
AND SURROUNDING SURFACE OBSERVATIONS.

FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 46.5N  54.2W   60 KT  70 MPH
 12H  03/1800Z 49.1N  48.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
 24H  04/0600Z 51.0N  38.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 36H  04/1800Z 53.0N  28.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 48H  05/0600Z...ABSORBED BY FRONTAL SYSTEM

$$
FORECASTER STEWART


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