Tropical Storm GREG

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TROPICAL STORM GREG DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072011
800 AM PDT WED AUG 17 2011

SATELLITE IMAGERY INDICATES THAT GREG HAS STRENGTHENED THIS MORNING 
AS A CENTRAL DENSE OVERCAST HAS DEVELOPED WITH AN OUTER CONVECTIVE
BAND OVER THE NORTHWESTERN SEMICIRCLE.  SATELLITE INTENSITY
ESTIMATES ARE 55 KT FROM TAFB AND 35 KT FROM SAB...SO THE INITIAL
INTENSITY IS INCREASED TO 45 KT.  ANALYSES FROM CIMSS AT THE
UNIVERSITY OF WISCONSIN SHOW 10-15 KT OF NORTHEASTERLY VERTICAL
WIND SHEAR STILL AFFECTING THE STORM...AND RECENT MICROWAVE DATA
SUPPORTS THIS BY SHOWING A SOMEWHAT SHEARED PATTERN TO THE
CONVECTION UNDERNEATH THE CDO.
 
THE INITIAL MOTION IS NOW 300/18...WHICH IS FASTER THAN BEFORE. 
GREG IS LOCATED BETWEEN A LARGE MID/UPPER-LEVEL RIDGE OVER THE
SOUTHERN UNITED STATES AND NORTHERN MEXICO AND A LARGE BUT WEAK
TROPICAL DISTURBANCE TO ITS WEST AND SOUTHWEST.  DURING THE NEXT
COUPLE OF DAYS...THE DISTURBANCE IS FORECAST TO WEAKEN DUE TO ITS
PROXIMITY TO GREG...LEAVING THE RIDGE TO THE NORTH AS THE MAIN
STEERING MECHANISM.  THIS EVOLUTION SHOULD STEER THE STORM QUICKLY
TOWARD THE WEST-NORTHWEST FOR 24 HR OR SO...FOLLOWED BY A GRADUAL
TURN TOWARD THE WEST AND A DECREASE IN FORWARD SPEED.  THE TRACK
GUIDANCE FOLLOWS THIS SCENARIO...ALTHOUGH THERE HAS BEEN A
NORTHWARD SHIFT LIKELY DUE TO THE INITIAL POSITION AND MOTION.  THE
NEW FORECAST TRACK IS FASTER THAN AND A LITTLE TO THE NORTH OF THE
PREVIOUS FORECAST...AND IT LIES CLOSE TO THE VARIOUS CONSENSUS
MODELS.

THE FORECAST TRAVCK KEEPS GREG OVER SEA SURFACE TEMPERATURES OF 27C
OR WARMER FOR 36 HR...AND THE DYNAMICAL MODELS FORECAST THE SHEAR
TO DECREASE DURING THIS TIME.  THIS COMBINATION SHOULD ALLOW
CONTINUED STRENGTHENING...AND THE NEW INTENSITY FORECAST CALLS FOR
A PEAK INTENSITY OF 75 KT IN 36 HR AS A BLEND BETWEEN THE SHIPS AND
LGEM MODELS.  AFTER 48 HR...THE WATERS GET COOLER ON THE FORECAST
TRACK...WHICH SHOULD INDUCE A STEADY WEAKENING TREND.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/1500Z 16.7N 104.2W   45 KT  50 MPH
 12H  18/0000Z 17.7N 106.6W   55 KT  65 MPH
 24H  18/1200Z 18.4N 109.4W   65 KT  75 MPH
 36H  19/0000Z 19.0N 111.8W   75 KT  85 MPH
 48H  19/1200Z 19.4N 113.6W   75 KT  85 MPH
 72H  20/1200Z 20.0N 116.5W   65 KT  75 MPH
 96H  21/1200Z 20.5N 119.0W   45 KT  50 MPH
120H  22/1200Z 20.5N 122.0W   30 KT  35 MPH
 
$$
FORECASTER BEVEN
 
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