000 WTPZ42 KNHC 172037 TCDEP2 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