000 WTPZ44 KNHC 250843 TCDEP4 TROPICAL STORM FRANK DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092010 200 AM PDT WED AUG 25 2010 CONVENTIONAL SATELLITE IMAGERY AND A RECENT AMSU-B OVERPASS INDICATE THAT FRANK HAS BECOME BETTER ORGANIZED THIS MORNING. THE IMAGERY REVEALS A WELL DEVELOPED BANDING FEATURE WITH -80C CLOUD TOPS EXTENDING OVER THE WESTERN HALF OVER THE CYCLONE...AND A STRONG BURST OF DEEP CONVECTION OVER THE CIRCULATION CENTER. BASED ON THE SATELLITE INTENSITY ESTIMATES OF 55 KT FROM BOTH TAFB AND SAB...AND RECENT TRENDS ASSOCIATED WITH THE DEVELOPING STRONG CONVECTIVE BAND...THE INITIAL INTENSITY IS ADJUSTED UP TO 60 KT. THE UW-CIMSS SHEAR PRODUCT SUGGESTS THAT SOME EASTERLY SHEAR IS IMPACTING THE CLOUD PATTERN...HOWEVER...THE UPPER FLOW IS QUITE DIFFLUENT... PARTICULARLY OVER THE WESTERN PORTION OF THE SYSTEM WHERE THE STRONG BAND RESIDES. THE OFFICIAL FORECAST CONTINUES TO CALL FOR FRANK TO STRENGTHEN INTO A HURRICANE...BUT SOONER THAN SHOWN IN THE PREVIOUS NHC FORECAST. THIS IS CONSISTENT WITH THE LATEST RUNS OF THE SHIPS AND LGEM INTENSITY MODELS. BEYOND THE 36 HOUR PERIOD...A GRADUAL WEAKENING IS FORECAST TO OCCUR AS AS THE CYCLONE TRAVERSES COOLER SEA SURFACE TEMPERATURES AND MOVES INTO A MORE STABLE AIR MASS. THE INITIAL MOTION IS A STEADY 285/8. FRANK IS MOVING WITHIN THE DEEP-LAYER EAST-SOUTHEASTERLY FLOW TO THE SOUTH OF A RIDGE OVER THE SOUTHWESTERN U.S. AND NORTHERN MEXICO. THIS GENERAL WEST- NORTHWESTWARD MOTION IS EXPECTED TO CONTINUE DURING THE NEXT 3 DAYS. AFTERWARD...THE AFOREMENTIONED RIDGE IS FORECAST TO WEAKEN IN RESPONSE TO A MID- TO UPPER-LEVEL TROUGH AMPLIFYING ALONG THE WEST COAST OF THE U.S. THIS CHANGE IN THE SYNOPTIC PATTERN SHOULD CAUSE FRANK TO DECREASE IN FORWARD SPEED AND TURN TOWARD THE NORTHWEST...AND THEN NORTHWARD INTO THE WEAKNESS BY DAY 5. THE TIGHTLY CLUSTERED DYNAMICAL MODELS HAVE AGAIN SHIFTED TO THE SOUTH OR LEFT OF THE PREVIOUS ADVISORY. CONSEQUENTLY...THE NHC OFFICIAL FORECAST FOLLOWS SUIT AND IS CLOSE TO THE MULTI-MODEL CONSENSUS... TVCN...AND THE ECMWF GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 25/0900Z 16.2N 103.6W 60 KT 12HR VT 25/1800Z 16.6N 105.0W 65 KT 24HR VT 26/0600Z 17.1N 106.8W 65 KT 36HR VT 26/1800Z 17.7N 108.7W 65 KT 48HR VT 27/0600Z 18.3N 110.3W 60 KT 72HR VT 28/0600Z 19.5N 112.5W 55 KT 96HR VT 29/0600Z 20.5N 113.5W 45 KT 120HR VT 30/0600Z 21.5N 113.5W 35 KT $$ FORECASTER ROBERTS/PASCH