ZCZC MIATCDEP3 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP182006 800 AM PDT THU OCT 26 2006 VISIBLE IMAGERY THIS MORNING SHOWS THAT THE AREA OF DISTURBED WEATHER THAT HAS BEEN SOUTH OF THE COAST OF MEXICO FOR THE PAST TWO DAYS IS NOW ORGANIZED ENOUGH TO BE DESIGNATED A TROPICAL DEPRESSION. THE CYCLONE HAS A SMALL AREA OF CENTRAL CONVECTION... WITH WELL-DEFINED OUTER BANDS IN ALL QUADRANTS EXCEPT THE SOUTH. SATELLITE INTENSITY ESTIMATES ARE 30 KT FROM TAFB AND SAB...AND THAT IS THE INITIAL INTENSITY. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/8. THE DEPRESSION IS ON THE SOUTHWEST SIDE OF A MID/UPPER-LEVEL RIDGE CENTERED OVER MEXICO. LARGE-SCALE MODELS ALL AGREE THAT THIS RIDGE SHOULD BUILD WESTWARD DURING THE NEXT 72 HR...WHICH SHOULD STEER THE DEPRESSION ON A GENERALLY WESTWARD TRACK. BY 96 HR...A SHORTWAVE TROUGH MOVING TOWARD CALIFORNIA SHOULD WEAKEN THE RIDGE...LEAVING THE DEPRESSION IN WEAK STEERING CURRENTS. THE MODELS FORECAST THE RIDGE TO RE-BUILD WEST OR WEST-NORTHWEST OF THE CYCLONE AFTER 96 HR...LEAVING THE CYCLONE ON THE WEST SIDE OF THE WEAKNESS AND TURNING SOUTHWESTWARD. THE FORECAST TRACK AFTER 72 HR IS SOMEWHAT LOW CONFIDENCE...AS THERE IS A CHANCE THE CYCLONE COULD TURN NORTHWARD INTO THE WEAKNESS IN THE RIDGE. THE DEPRESSION IS CURRENTLY IN AN ENVIRONMENT OF LIGHT SOUTHEASTERLY SHEAR...AND THE LARGE-SCALE MODELS FORECAST A LIGHT SHEAR ENVIRONMENT TO PERSIST THROUGH 72 HR. THE INTENSITY FORECAST CALLS FOR STEADY SLOW STRENGTHENING...ALTHOUGH DUE TO THE SMALL INNER CORE THERE IS A CHANCE IT COULD STRENGTHEN FASTER. AFTER 72 HR... THE MODELS DIVERGE ON THE AMOUNT OF SHEAR CAUSED BY THE SHORTWAVE TROUGH. THE GFS KEEPS ENOUGH UPPER-LEVEL RIDGING BETWEEN THE DEPRESSION AND THE TROUGH TO KEEP THE SHEAR LIGHT. ON THE OTHER HAND...THE ECMWF AND NOGAPS FORECAST 20-25 KT OF NORTHWESTERLY SHEAR...AND THE UKMET FORECASTS A VERY UNFAVORABLE 40-60 KT OF NORTHWESTERLY SHEAR. THE INTENSITY FORECAST WILL LEAN ON THE ECMWF/NOGAPS SOLUTIONS TO FORECAST A SLOW WEAKENING AFTER 72 HR. FORECAST POSITIONS AND MAX WINDS INITIAL 26/1500Z 16.8N 104.2W 30 KT 12HR VT 27/0000Z 17.1N 105.5W 35 KT 24HR VT 27/1200Z 17.1N 107.1W 40 KT 36HR VT 28/0000Z 17.1N 108.5W 45 KT 48HR VT 28/1200Z 17.1N 110.0W 50 KT 72HR VT 29/1200Z 17.0N 112.5W 60 KT 96HR VT 30/1200Z 17.0N 113.5W 55 KT 120HR VT 31/1200Z 16.5N 114.5W 50 KT $$ FORECASTER BEVEN NNNN
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Page last modified: Thursday, 26-Oct-2006 14:40:03 UTC