ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION NINE-E DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092010 200 PM PDT SAT AUG 21 2010 THE AREA OF LOW PRESSURE SOUTH-SOUTHEAST OF THE GULF OF TEHUANTEPEC HAS BECOME BETTER ORGANIZED TODAY...WITH AN INCREASE IN DEEP CONVECTION NEAR THE ESTIMATED CENTER LOCATION AND THE DEVELOPMENT OF MULTIPLE CURVED CONVECTIVE BANDS. THEREFORE...ADVISORIES ARE INITIATED AT THIS TIME...AND THE INITIAL INTENSITY IS SET AT 25 KT IN AGREEMENT WITH THE DVORAK ESTIMATE FROM TAFB AT 1800 UTC. ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR AT LEAST STEADY INTENSIFICATION IN THE SHORT TERM...AS THE DEPRESSION IS SITUATED BENEATH AN UPPER-LEVEL ANTICYCLONE AND OVER VERY WARM WATERS OF ALMOST 30C. BEYOND THE NEXT 24 HOURS OR SO...THE INTENSITY OF THE CYCLONE WILL BE PRIMARY DETERMINED BY HOW MUCH IT INTERACTS WITH THE COAST OF MEXICO. THE CURRENT OFFICIAL FORECAST ASSUMES THE CENTER WILL REMAIN OFFSHORE AND IS CLOSE TO THE SHIPS MODEL IN THE SHORT TERM AND FOLLOWS A BLEND OF THE SHIPS AND LGEM LATE IN THE PERIOD. THE DEPRESSION IS CURRENTLY SITUATED IN A WEAK STEERING ENVIRONMENT...AND SOME ERRATIC MOTION IS POSSIBLE AS THE SYSTEM DEVELOPS OVER THE NEXT 12 TO 24 HOURS. BEYOND THAT TIME...THE GLOBAL MODELS SHOW A DEEP-LAYER RIDGE BUILDING NORTH OF THE CYCLONE...WHICH SHOULD RESULT IN AN INCREASING WESTWARD MOTION OVER THE NEXT TWO OR THREE DAYS. BOTH THE GFS AND UKMET SHOW THE CYCLONE MOVING ONSHORE...ALTHOUGH THE GFS SHOWS THE DEPRESSION INTERACTING WITH A SECOND VORTEX DURING THIS TIME THAT NONE OF THE OTHER GUIDANCE SHOWS. THE OFFICIAL FORECAST SHOWS A SLOW WESTWARD MOTION FOR THE FIRST 2 TO 3 DAYS WITH A TURN TOWARD THE WEST-NORTHWEST AT DAYS 4 AND 5 AS THE RIDGE LIFTS NORTH. THIS SOLUTION REPRESENTS A BLEND OF THE GLOBAL MODEL AND ENSEMBLE GUIDANCE...EXCLUDING THE GFS. THIS INITIAL TRACK FORECAST HAS LARGER THAN USUAL UNCERTAINTY DUE TO THE WEAK INITIAL STEERING PATTERN AND POTENTIAL INTERACTION WITH THE MONSOON FLOW AND LAND. GIVEN THE CONSIDERABLE TRACK FORECAST UNCERTAINTY...A TROPICAL STORM WATCH HAS BEEN ISSUED FOR PORTIONS OF THE COAST OF MEXICO. FORECAST POSITIONS AND MAX WINDS INITIAL 21/2100Z 13.9N 93.2W 25 KT 12HR VT 22/0600Z 13.9N 93.6W 35 KT 24HR VT 22/1800Z 13.8N 94.5W 40 KT 36HR VT 23/0600Z 13.7N 95.6W 50 KT 48HR VT 23/1800Z 13.7N 96.6W 55 KT 72HR VT 24/1800Z 14.0N 98.5W 65 KT 96HR VT 25/1800Z 15.0N 101.0W 65 KT 120HR VT 26/1800Z 16.0N 103.5W 65 KT $$ FORECASTER BRENNAN NNNN
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