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Tropical Storm GERT (Text)

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TROPICAL STORM GERT DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072011
500 PM AST MON AUG 15 2011
 
RADAR DATA FROM BERMUDA AND SATELLITE IMAGERY INDICATE GERT HAS
CHANGED LITTLE IN APPEARANCE SINCE THE PREVIOUS ADVISORY. THE LAST
RECON FLIGHT LEG THROUGH THE SOUTHEAST QUADRANT PRODUCED AN 850 MB
FLIGHT-LEVEL WIND OF 61 KT...WHICH EQUATES TO ROUGHLY 49 KT AT THE
SURFACE. GIVEN THE APPARENT STEADY NATURE OF THE CYCLONE...THE
INTENSITY IS BEING HELD AT 50 KT FOR THIS ADVISORY...WHICH IS CLOSE
TO A BLEND OF SATELLITE ESTIMATES OF 55 KT FROM TAFB AND 45 KT FROM
SAB...RESPECTIVELY . UPPER-LEVEL OUTFLOW IS FAIR IN ALL
QUADRANTS...EXCEPT RESTRICTED TO THE NORTHEAST.

THERE IS NO CHANGE TO THE PREVIOUS FORECAST RATIONALE. GERT HAS
MOVED NORTH OF THE SUBTROPICAL RIDGE AXIS AND IS NOW MOVING TO THE
NORTH-NORTHEAST OR 020/12. A GRADUAL TURN TOWARD THE NORTHEAST
ACCOMPANIED BY A STEADY INCREASE IN FORWARD SPEED IS EXPECTED
THROUGH THE REMAINDER OF THE FORECAST PERIOD AS GERT COMES UNDER
THE INFLUENCE OF INCREASING SOUTHWESTERLY FLOW AHEAD OF A LARGE
DEEP-LAYERED MID-LATITUDE TROUGH CURRENTLY MOVING EASTWARD OFF THE
U.S. EAST COAST. THE NHC FORECAST TRACK IS A LITTLE TO EAST OF THE
PREVIOUS ADVISORY TRACK AFTER 12 HOURS...AND LIES ALONG THE EXTREME
RIGHT SIDE OF THE NHC GUIDANCE ENVELOPE.

THE WINDOW OF OPPORTUNITY FOR GERT TO INTENSIFY IS GRADUALLY COMING
TO A CLOSE. THE CYCLONE WILL BE OVER AT LEAST 26C SSTS FOR ANOTHER
12 HOURS OR SO WHILE THE VERTICAL SHEAR IS STILL LOW. ALTHOUGH THE
OFFICIAL INTENSITY FORECAST ONLY CALLS FOR GERT TO REACH 55 KT...IT
IS POSSIBLE THAT CYCLONE COULD REACH 60 KT BETWEEN THE 12- AND
24-HOUR FORECAST PERIODS DURING THE NOCTURNAL CONVECTIVE MAXIMUM
PERIOD AROUND 12Z TUESDAY MORNING. BY 36 HOURS...GERT WILL BE OVER
NEAR-20C SSTS AND UNDERGOING EXTRATROPICAL TRANSITION. THE
POST-TROPICAL LOW IS THEN FORECAST TO MERGE WITH A FRONTAL SYSTEM
OVER THE FAR NORTH ATLANTIC SHORTLY AFTER 48 HOURS. THE INTENSITY
FORECAST CLOSELY FOLLOWS THE SHIPS AND LGEM MODEL SOLUTIONS...AND
EXTRATROPICAL INTENSITY FORECASTS PROVIDED BY THE NOAA OCEAN
PREDICTION CENTER.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/2100Z 33.2N  62.7W   50 KT  60 MPH
 12H  16/0600Z 35.7N  60.8W   55 KT  65 MPH
 24H  16/1800Z 38.9N  57.1W   55 KT  65 MPH
 36H  17/0600Z 41.7N  51.8W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  17/1800Z 44.6N  45.2W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  18/1800Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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