000
WTNT42 KNHC 142041
TCDAT2
 
TROPICAL STORM GERT DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072011
500 PM AST SUN AUG 14 2011
 
DEEP CONVECTION HAS CONTINUED TO DEVELOP OVER THE CENTER OF TROPICAL
STORM GERT AND SMALL BANDING FEATURES HAVE BEEN TRYING TO DEVELOP
IN THE NORTH AND EAST QUADRANTS OF THE CIRCULATION. AN AIR FORCE
RESERVE UNIT RECONNAISSANCE AIRCRAFT INVESTIGATING THE CYCLONE THIS
AFTERNOON FOUND MAXIMUM 850 MB FLIGHT-LEVEL WINDS OF 43 KT IN THE
SOUTHEAST QUADRANT ALONG WITH UNCONTAMINATED SFMR WINDS OF 39 AND
41 KT. THE SFMR WINDS CORRELATE WELL WITH AN EARLIER 1324Z ASCAT
PASS THAT INDICATED SURFACE WINDS OF NEAR 40 KT IN THE SAME GENERAL
AREA OF THE CYCLONE CIRCULATION. BASED ON THE RECENT SFMR WINDS AND
EARLIER ASCAT WINDS...THE INITIAL INTENSITY IS INCREASED TO 40 KT.

NOW THAT GERT HAS REDEVELOPED DEEP CONVECTION NEAR THE CENTER AND
HAS BECOME A MORE VERTICALLY DEEP SYSTEM...THE TROPICAL STORM HAS
STARTED MOVING NORTH-NORTHWESTWARD...OR 335/07...TOWARD A WEAKNESS
IN THE SUBTROPICAL RIDGE. WATER VAPOR IMAGERY INDICATES A
FAST-MOVING SHORTWAVE TROUGH PASSING EASTWARD OVER AND NORTH OF
BERMUDA WITH A SHORTWAVE RIDGE IN ITS WAKE...WHICH MAY ALLOW FOR
THE SUBTROPICAL RIDGE TO BRIEFLY BUILD BACK WESTWARD AND CREATE
SOME STAIR-STEP MOTIONS TO THE NORTH-NORTHWEST AND NORTH.
HOWEVER...ALL OF THE GLOBAL MODELS ARE IN EXCELLENT AGREEMENT ON A
LARGE MID-LATITUDE TROUGH CURRENTLY OVER THE EASTERN U.S. MOVING
STEADILY EASTWARD AND GRADUALLY ERODING THE WESTERN PERIPHERY OF
THE MID-LEVEL RIDGE ALONG 32N LATITUDE FOR THE NEXT 24-36 HOURS. AS
A RESULT... THE STEERING FLOW SHOULD BECOME MORE SOUTHERLY AND
STEER GERT NORTHWARD FOR THE NEXT 24 HOURS OR SO...AND THEN
ACCELERATE THE CYCLONE NORTHEASTWARD THROUGH THE REMAINDER OF THE
FORECAST PERIOD. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE
PREVIOUS ADVISORY THROUGH 48 HOURS AND LIES CLOSE TO THE TIGHTLY
PACKED GLOBAL MODEL SUITE.

GERT HAS MOVED INTO A WEAK VERTICAL SHEAR REGION ON THE NORTH SIDE
OF A SMALL UPPER-LEVEL LOW...WHICH HAS ALLOWED DEEP CONVECTION TO
PERSIST AND PRODUCE A SMALL UPPER-LEVEL ANTICYCLONE OVER THE STORM.
THIS FAVORABLE UPPER-LEVEL FLOW REGIME...ALONG WITH WARM SSTS ABOVE
28C...IS EXPECTED TO PERSIST FOR THE NEXT 24 HOURS OT SO. THIS
SHOULD ALLOW FOR AT LEAST MODEST STRENGTHENING. AFTER
THAT...THERMODYNAMIC CONDITIONS ARE FORECAST BECOME LESS
CONDUCIVE...WHICH SHOULD ALLOW FOR ONLY SLIGHT STRENGTHENING EVEN
THOUGH THE VERTICAL SHEAR IS EXPECTED TO BE FAIRLY LOW. BY 48
HOURS...GERT WILL BE MOVING OVER MUCH COOLER WATER AND
SOUTHWESTERLY VERTICAL SHEAR IS EXPECTED TO INCREASE ABOVE 30 KT.
THIS COMBINATION OF UNFAVORABLE ENVIRONMENTAL CONDITIONS SHOULD
CAUSE GERT TO MAKE THE TRANSITION INTO A POST-TROPICAL CYCLONE. THE
INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND CLOSELY
FOLLOWS THE SHIPS AND LGEM INTENSITY MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  14/2100Z 28.9N  63.2W   40 KT  45 MPH
 12H  15/0600Z 30.3N  63.8W   40 KT  45 MPH
 24H  15/1800Z 32.3N  63.6W   45 KT  50 MPH
 36H  16/0600Z 34.9N  61.8W   50 KT  60 MPH
 48H  16/1800Z 38.9N  58.2W   50 KT  60 MPH
 72H  17/1800Z 46.0N  45.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  18/1800Z...DISSIPATED
 
$$
FORECASTER STEWART