[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 290249
TCDAT1

TROPICAL STORM OPHELIA DISCUSSION NUMBER  26
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
1100 PM AST WED SEP 28 2011

AIRCRAFT DATA INDICATE THAT OPHELIA HAS STRENGTHENED.  PEAK
FLIGHT-LEVEL WINDS WERE 64 KT...WITH BELIEVABLE SFMR VALUES NEAR 50
KT.  THUS THE INITIAL WIND SPEED IS RAISED TO 50 KT.  ALTHOUGH THE
STORM HAS BECOME A LITTLE STRONGER...INFRARED SATELLITE IMAGES ARE
NOT PARTICULARLY IMPRESSIVE WITH A SMALL AREA OF CONVECTION
NORTHEAST OF THE CENTER ALONG WITH A LARGER CURVED BAND IN THE
SOUTHEAST QUADRANT.  MICROWAVE DATA...HOWEVER...DOES SHOW A
BETTER-ORGANIZED CORE WITH PERHAPS THE PRIMITIVE STAGES OF AN EYE.
IT IS INTERESTING THAT OPHELIA HAS INTENSIFIED A GOOD DEAL TODAY
DESPITE AN UPPER-LEVEL TROUGH CAUSING 20-25 KT OF SOUTHWESTERLY
SHEAR.  AS THIS TROUGH TO THE NORTHWEST OF OPHELIA PULLS
AWAY...UPPER RIDGING SHOULD BUILD IN CLOSER TO THE CYCLONE
AND CAUSE THE SHEAR TO RELAX TO MORE MODERATE LEVELS.  STEADY
INTENSIFICATION WOULD SEEM TO BE THE BEST BET...AND THE NHC
FORECAST COULD BE ON THE CONSERVATIVE SIDE IF AN INNER CORE BECOMES
ORGANIZED.  THE NEW FORECAST IS SIMILAR TO THE PREVIOUS ONE BUT
SHOWS A HIGHER PEAK INTENSITY AT 72 HOURS...SPLITTING THE
DIFFERENCE BETWEEN THE STATISTICAL AND DYNAMICAL GUIDANCE.
WEAKENING SHOULD BEGIN AFTER DAY 3 DUE TO COOLING WATERS AND
INCREASING SOUTHWESTERLY SHEAR.

THE AIRCRAFT FIXES INDICATE THAT CYCLONE IS MOVING A BIT SLOWER...
ABOUT 325/5.  THE GLOBAL MODELS ARE IN RATHER GOOD AGREEMENT ON
OPHELIA PICKING UP SOME FORWARD SPEED AS IT MOVES ON A TRACK TOWARD
THE NORTH-NORTHWEST AND NORTH OVER THE NEXT COUPLE OF DAYS ALONG
THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE.  THEREAFTER...
THE CYCLONE SHOULD START TO ACCELERATE TO THE NORTH-NORTHEAST DUE
TO INCREASING SOUTHWESTERLY FLOW BETWEEN THE RIDGE AND A LARGE
MID-TROPOSPHERIC TROUGH MOVING OFF THE U.S. EAST COAST.  WHILE THE
GUIDANCE HAS BEEN STRUGGLING WITH THE INTERACTION OF THE TROPICAL
CYCLONE WITH THE MID-LATITUDE FLOW...IN GENERAL THE GUIDANCE HAS
SHIFTED A BIT TO THE LEFT AFTER DAY 3...AND THE NHC FORECAST
FOLLOWS SUIT.  THE MOST CONSISTENT MODEL HAS BEEN THE ECMWF SINCE
YESTERDAY...AND THE OFFICIAL FORECAST WILL STAY BETWEEN THAT MODEL
AND THE HFIP MULTI-MODEL CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 19.4N  60.7W   50 KT  60 MPH
 12H  29/1200Z 20.3N  61.3W   55 KT  65 MPH
 24H  30/0000Z 21.9N  62.0W   60 KT  70 MPH
 36H  30/1200Z 23.7N  62.8W   65 KT  75 MPH
 48H  01/0000Z 26.1N  63.1W   70 KT  80 MPH
 72H  02/0000Z 32.5N  62.0W   80 KT  90 MPH
 96H  03/0000Z 43.0N  57.5W   65 KT  75 MPH
120H  04/0000Z 54.0N  47.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BLAKE



This weather bulletin was brought to you by:
www.nashvilleweather.net