Tropical Storm GREG

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TROPICAL STORM GREG DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072011
200 PM PDT WED AUG 17 2011

GREG CONTINUES TO STRENGTHEN THIS AFTERNOON...WITH SATELLITE IMAGERY
SHOWING A CENTRAL DENSE OVERCAST WITH WELL-DEFINED OUTER BANDING IN
ALL QUADRANTS EXCEPT THE NORTHEAST.  THERE HAS BEEN AN OCCASIONAL
DIMPLE IN THE CDO THAT MIGHT BE A FORMATIVE EYE.  HOWEVER...THERE
IS NO RECENT MICROWAVE IMAGERY TO CONFIRM THE DEVELOPMENT OF AN
EYEWALL.  SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND
SAB...AND THAT IS THE INITIAL INTENSITY.  THE CIRRUS OUTFLOW IS
GOOD IN THE WESTERN SEMICIRCLE AND POOR IN THE EASTERN SEMICIRCLE.

THE INITIAL MOTION IS 290/20.  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.  THIS DISTURBANCE SHOULD SLOWLY 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.  WHILE THE
GLOBAL MODELS AGREE WITH THIS SCENARIO... MOST OF THEM HAD TOO WEAK
OF AN INITIALIZATION OF GREG AND SEEM TO BE TURNING THE STORM TOO
QUICKLY WESTWARD INTO THE DISTURBANCE.  THE MODEL WITH THE BEST
INITIAL REPRESENTATION OF GREG...NOGAPS...FORECASTS A TRACK NEAR
THE NORTH EDGE OF THE GUIDANCE ENVELOPE.  OVERALL...THE TRACK
GUIDANCE HAS SHIFTED SIGNIFICANTLY SOUTHWARD FROM THE PREVIOUS
ADVISORY.  THE NEW FORECAST TRACK WILL ALSO SHIFT A LITTLE TO THE
SOUTH.  HOWEVER...IT LIES ON THE RIGHT SIDE OF THE GUIDANCE
ENVELOPE BETWEEN THE NOGAPS AND THE CONSENSUS MODELS.
 
THE FORECAST TRACK KEEPS GREG OVER SEA SURFACE TEMPERATURES OF 27C
OR WARMER FOR 24-36 HR...AND THE DYNAMICAL MODELS FORECAST LIGHT
VERTICAL WIND SHEAR DURING THIS TIME.  THIS COMBINATION SHOULD
ALLOW CONTINUED STRENGTHENING...AND THE NEW INTENSITY FORECAST
CALLS FOR A PEAK INTENSITY OF 80 KT IN 36 HR AS A BLEND BETWEEN THE
SHIPS AND LGEM MODELS.  AFTER 36 HR...THE WATERS GET COOLER ON THE
FORECAST TRACK...WHICH SHOULD INDUCE A STEADY WEAKENING TREND.  THE
RAPID INTENSIFICATION INDEX OF THE SHIPS MODEL SHOWS A 40 PERCENT
CHANCE OF A 25 KT INTENSIFICATION DURING THE NEXT 24 HR AND A 20
PERCENT CHANCE OF A 40 KT INTENSIFICATION.  THUS...IT CANNOT BE
RULED OUT THAT GREG COULD GET MUCH STRONGER THAN CURRENTLY
FORECAST.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/2100Z 17.1N 106.5W   55 KT  65 MPH
 12H  18/0600Z 17.9N 109.0W   65 KT  75 MPH
 24H  18/1800Z 18.5N 111.8W   75 KT  85 MPH
 36H  19/0600Z 18.9N 113.9W   80 KT  90 MPH
 48H  19/1800Z 19.2N 115.6W   75 KT  85 MPH
 72H  20/1800Z 19.5N 118.5W   60 KT  70 MPH
 96H  21/1800Z 20.0N 121.5W   40 KT  45 MPH
120H  22/1800Z 20.0N 123.5W   25 KT  30 MPH
 
$$
FORECASTER BEVEN
 
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