[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 161435
TCDAT2

TROPICAL STORM GERT DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072011
ISSUED BY THE HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1100 AM AST TUE AUG 16 2011

GERT CONTINUES TO WEAKEN THIS MORNING...WITH THE ASSOCIATED
THUNDERSTORM ACTIVITY VIRTUALLY EVAPORATING AROUND 10Z.  MORNING
SATELLITE IMAGERY...AND TO SOME DEGREE DETERMINISTIC MODEL
GUIDANCE...IMPLIED THAT GERT HAS ABOUT 10 KNOTS OF NORTHEASTERLY
VERTICAL WIND SHEAR DUE TO THE STRONGER SOUTHWESTERLY LOW-LEVEL
FLOW CONFLICTING WITH LIGHTER SOUTHWEST WINDS AT THE 300 HPA LEVEL.
THE LOW-LEVEL CENTER REMAINS EXPOSED...THOUGH NEW CONVECTION IS
TRYING TO DEVELOP ON ITS NORTHEAST SIDE WHICH COULD BE AN INDICATION
OF A SWITCH IN THE DIRECTION OF THE VERTICAL WIND SHEAR TO
SOUTHWESTERLY...WHICH WAS PREVIOUSLY ANTICIPATED.  THE INITIAL WIND
SPEED HAS BEEN LOWERED TO 35 KT FOR THIS ADVISORY...IN LINE WITH
THE CURRENT T-NUMBER FROM TAFB BUT HIGHER THAN THAT PROVIDED BY
SAB.  THIS SYSTEM STILL HAS A FEW MORE HOURS BEFORE IT CROSSES THE
26C ISOTHERM...WHICH SHOULD ALLOW IT TO RETAIN ITS CURRENT
INTENSITY.  GERT IS FORECAST TO BECOME A POST-TROPICAL CYCLONE IN
ABOUT 12 HOURS AS IT MOVES OVER WATERS NEAR 20C AND INTERACTS WITH
THE APPROACHINIG COLD FRONT...WHICH COULD LEAD TO TEMPORARY
RESTRENGTHENING...SO THE INTENSITY FORECAST HAS BEEN LEFT
RELATIVELY UNCHANGED.  THE RESULTANT LOW PRESSURE AREA SHOULD LOSE
DEFINITION WITHIN THE FRONTAL ZONE DURING THE DAY WEDNESDAY.

THE TROPICAL STORM IS ACCELERATING INTO THE NORTH ATLANTIC
WATERS...AND THE LATEST INITIAL MOTION ESTIMATE IS 040/26. THIS
SYSTEM COULD ACCELERATE SLIGHTLY MORE AS GERT BECOMES INCREASINGLY
STEERED BY THE STRONG LOW-LEVEL FLOW TO THE EAST OF A DEEP-LAYER
TROUGH ALONG THE UNITED STATES EAST COAST. THE OFFICIAL FORECAST IS
SLIGHTLY TO THE LEFT OF THE PREVIOUS ONE BUT REMAINS ON THE
EASTWARD SIDE OF THE GUIDANCE ENVELOPE.  THE FORECAST TRACK AND
TIMING OF EXTRATROPICAL TRANSITION INCORPORATE IDEAS COMMUNICATED
BY THE OCEAN PREDICTION CENTER.



FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 38.1N  57.5W   35 KT  40 MPH
 12H  17/0000Z 41.0N  54.2W   35 KT  40 MPH
 24H  17/1200Z 44.3N  49.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 36H  18/0000Z...POST-TROP/EXTRATROP

$$
FORECASTER ROTH


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