000 WTPZ42 KNHC 171444 TCDEP2 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