000 WTPZ44 KNHC 221458 TCDEP4 TROPICAL STORM FRANK DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092010 800 AM PDT SUN AUG 22 2010 THE CLOUD PATTERN ASSOCIATED WITH THE CYCLONE HAS CONTINUED TO BECOME BETTER ORGANIZED...AND 1200 UTC DVORAK ESTIMATES WERE 2.5 FROM SAB AND 3.0 FROM TAFB. BASED ON A BLEND OF THE SATELLITE ESTIMATES...THE DEPRESSION IS UPGRADED TO A TROPICAL STORM AND THE INITIAL INTENSITY IS SET AT 40 KNOTS. THE SHIPS MODEL AND UW-CIMSS SATELLITE ANALYSIS SHOW THAT FRANK IS LOCATED IN A LOW SHEAR ENVIRONMENT. THIS...COMBINED WITH WARM WATERS AND A VERY MOIST LOWER TO MID-TROPOSPHERE SUGGEST THAT STRENGTHENING IS LIKELY. HOWEVER...THE SHIPS MODEL SHOWS THE SHEAR INCREASING TO 15 TO 20 KNOTS IN THE NEXT 12 TO 24 HOURS...WHICH COULD TEMPER INTENSIFICATION SOMEWHAT. THE OFFICIAL FORECAST IS ADJUSTED UPWARD THROUGH THE FIRST 48 HOURS AND IS CLOSE TO A BLEND OF THE SHIPS AND LGEM THROUGH THE PERIOD. AN 0804 UTC AMSR-E PASS AND 1201 UTC SSM/I PASS WERE HELPFUL IN LOCATING THE CENTER...WHICH IS LOCATED A LITTLE FARTHER NORTH AND WEST THAN PREVIOUSLY ESTIMATED. THE INITIAL MOTION ESTIMATE IS 270/6...AS THE CYCLONE IS BEING STEERED BY A DEEP-LAYER RIDGE CENTERED OVER THE SOUTHWESTERN UNITED STATES. ALL OF THE GLOBAL MODEL AND ENSEMBLE GUIDANCE IS IN GOOD AGREEMENT SHOWING THE CORE OF THE RIDGE SHIFTING NORTHWESTWARD DURING THE FORECAST PERIOD... AND THIS SHOULD ALLOW FRANK TO TURN GRADUALLY TOWARD THE WEST-NORTHWEST WITHIN A DAY OR SO...AND REMAIN ON THAT HEADING THROUGH THE FORECAST PERIOD. WHILE MOST OF THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO...THERE REMAINS CONSIDERABLE DISAGREEMENT ON HOW CLOSE FRANK WILL GET TO THE COAST OF MEXICO. THE OFFICIAL FORECAST HAS BEEN ADJUSTED NORTHWARD TOWARD THE TVCN MULTI-MODEL CONSENSUS...AND IS FASTER THAN THE PREVIOUS PACKAGE. GIVEN THE ADJUSTMENTS TO THE TRACK FORECAST...A TROPICAL STORM WARNING IS NOW NEEDED FOR PORTIONS OF THE MEXICAN COAST. BASED ON THE OFFICIAL FORECAST AND PREVIOUS NHC FORECAST ERRORS...THERE IS ABOUT A 20 TO 35 PERCENT CHANCE OF TROPICAL STORM FORCE WINDS AFFECTING ANY INDIVIDUAL POINT LOCATION WITHIN THE WARNING AREA. FORECAST POSITIONS AND MAX WINDS INITIAL 22/1500Z 14.0N 95.3W 40 KT 12HR VT 23/0000Z 14.1N 96.3W 50 KT 24HR VT 23/1200Z 14.2N 97.8W 60 KT 36HR VT 24/0000Z 14.6N 99.3W 65 KT 48HR VT 24/1200Z 15.1N 100.8W 65 KT 72HR VT 25/1200Z 16.5N 103.5W 70 KT 96HR VT 26/1200Z 17.5N 106.0W 70 KT 120HR VT 27/1200Z 18.5N 109.0W 70 KT $$ FORECASTER BRENNAN