000 WTPZ44 KNHC 271431 TCDEP4 HURRICANE FRANK DISCUSSION NUMBER 24 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092010 800 AM PDT FRI AUG 27 2010 FRANK CONTINUES TO WEAKEN. THE CLOUD PATTERN CONSISTS OF A SMALL AREA OF PULSATING DEEP CONVECTION JUST TO THE WEST OF THE ESTIMATED CENTER...WITH VERY LITTLE IN THE WAY OF BANDING FEATURES. DVORAK T-NUMBERS FROM SAB AND TAFB ARE 3.5 AND 4.5 RESPECTIVELY. ALTHOUGH THE DVORAK RULES SPECIFY 77 KT FOR THE CURRENT INTENSITY...THESE RULES HAVE BEEN KNOWN TO YIELD A HIGH BIAS FOR WEAKENING TROPICAL CYCLONES. USING A BLEND OF T-NUMBERS AND CURRENT INTENSITY VALUES...THE WIND SPEED IS SET TO 65 KT FOR THIS ADVISORY. WITH THE CYCLONE MOVING ACROSS A GRADIENT OF DECREASING SEA SURFACE TEMPERATURES...STEADY WEAKENING IS PREDICTED. THE OFFICIAL INTENSITY FORECAST FOLLOWS THE STATISTICAL/DYNAMICAL LGEM GUIDANCE RATHER CLOSELY. FRANK IS PREDICTED TO DROP BELOW TROPICAL STORM STRENGTH IN ABOUT 48 HOURS...HOWEVER THIS EVENT COULD EASILY OCCUR SOONER. FIRST-LIGHT VISIBLE IMAGES SHOW THAT THE CENTER OF FRANK HAS NOT MOVED AS FAR TO THE WEST-NORTHWEST AS EARLIER ESTIMATED...AND THIS REQUIRES A SLIGHT EASTWARD RELOCATION FOR THIS PACKAGE. BASED ON THE ADJUSTMENTS TO THE TRACK...THE FORWARD MOTION IS ESTIMATED TO HAVE SLOWED TO NEAR 5 KT. EVEN FURTHER DECELERATION IS LIKELY AS THE MID-LEVEL RIDGE TO THE NORTH OF FRANK CONTINUES TO BREAK DOWN DUE TO A DIGGING 500 MB TROUGH OVER CALIFORNIA. SINCE THE SYSTEM SHOULD BE REDUCED TO A SHALLOW CYCLONE IN 2-3 DAYS... IT WILL PROBABLY NOT RESPOND MUCH TO THE STEERING FLOW ASSOCIATED WITH THE ABOVE MENTIONED TROUGH. THEREFORE...THE OFFICIAL TRACK FORECAST SLOWS THE FORWARD SPEED TO A CRAWL LATER IN THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INITIAL 27/1500Z 18.8N 112.0W 65 KT 12HR VT 28/0000Z 19.3N 112.7W 55 KT 24HR VT 28/1200Z 20.0N 113.6W 45 KT 36HR VT 29/0000Z 20.8N 114.0W 40 KT 48HR VT 29/1200Z 21.2N 114.0W 35 KT 72HR VT 30/1200Z 22.0N 114.0W 30 KT 96HR VT 31/1200Z 22.5N 114.0W 25 KT...POST-TROP/REMNT LOW 120HR VT 01/1200Z 23.0N 114.0W 20 KT...POST-TROP/REMNT LOW $$ FORECASTER PASCH