[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 230852
TCDAT1

TROPICAL STORM OPHELIA DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
500 AM AST FRI SEP 23 2011

OPHELIA CONTINUES TO STRUGGLE AGAINST STRONG SOUTHWESTERLY SHEAR.
THE CENTER OF THE TROPICAL STORM REMAINS EXPOSED WELL TO THE WEST OF
A LARGE CURVED BAND...ALTHOUGH THIS BAND IS AT A CONSIDERABLE
DISTANCE FROM THE CENTER.  WITH LITTLE CONVECTION NEAR THE
CENTER...IT IS LIKELY THE WINDS HAVE DROPPED SINCE THE LAST
ADVISORY...AND THE INITIAL WIND SPEED IS 40 KT.  FURTHER WEAKENING
IS FORECAST DUE TO THE PERSISTENT SHEAR FROM AN UPPER-LEVEL
TROUGH...AND THE INTENSITY FORECAST IS LOWERED FROM THE PREVIOUS
PREDICTION.  IT IS ALSO QUITE POSSIBLE THAT OPHELIA WILL WEAKEN
INTO A REMNANT LOW SOMETIME DURING THE NEXT COUPLE OF DAYS.  IF
OPHELIA SURVIVES...THE UPPER-LEVEL ENVIRONMENT COULD BECOME MORE
FAVORABLE FOR STRENGTHENING AT DAYS 4 AND 5...SO SOME
INTENSIFICATION IS SHOWN AT THOSE TIMES.

THE INITIAL MOTION IS 290/11.  A GRADUAL TURN TO THE RIGHT IS
ANTICIPATED OVER THE NEXT DAY OR SO AS OPHELIA MOVES AROUND THE
SOUTHERN PERIPHERY OF A RIDGE OVER THE WESTERN ATLANTIC OCEAN.
THERE ARE SOME RATHER LARGE DIFFERENCES IN THE GLOBAL MODEL TRACKS
ALMOST IMMEDIATELY...WHICH SEEM TO BE RELATED TO THE DEPTH OF THE
TROPICAL CYCLONE.  GENERALLY...THE MODELS THAT SHOW A WEAKER
CYCLONE...SUCH AS THE ECMWF...SHOW THE WEST-NORTHWESTWARD MOTION
CONTINUING FOR THE NEXT SEVERAL DAYS UNDER THE RIDGE.  THE
GFS/HWRF/GFDL MODELS HAVE A MORE VERTICALLY COHERENT TROPICAL
CYCLONE WHICH IS AFFECTED MORE BY THE SOUTHWESTERLY UPPER-LEVEL
FLOW.  THIS DEEPER STRUCTURE CAUSES THE CYCLONE TO MOVE TOWARD THE
NORTHWEST AND NORTH-NORTHWEST...TO THE RIGHT OF THE BULK OF THE
GUIDANCE. GIVEN THAT OPHELIA IS EXPECTED TO WEAKEN AND BECOME MORE
SHALLOW...THE NHC FORECAST IS SHIFTED TO THE LEFT...BUT NOT QUITE
AS FAR TO THE WEST AS THE ECMWF OR BAM SHALLOW MODELS.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 14.5N  51.0W   40 KT  45 MPH
 12H  23/1800Z 15.3N  52.7W   35 KT  40 MPH
 24H  24/0600Z 16.7N  55.0W   30 KT  35 MPH
 36H  24/1800Z 18.0N  57.0W   30 KT  35 MPH
 48H  25/0600Z 19.2N  58.9W   30 KT  35 MPH
 72H  26/0600Z 21.0N  62.0W   30 KT  35 MPH
 96H  27/0600Z 23.0N  64.5W   35 KT  40 MPH
120H  28/0600Z 25.5N  66.0W   40 KT  45 MPH

$$
FORECASTER BLAKE


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