ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION NINE-E DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008 200 PM PDT WED AUG 06 2008 THE LOW PRESSURE SYSTEM WELL SOUTHWEST OF THE PACIFIC COAST OF MEXICO HAS STEADILY BEEN GAINING ORGANIZATION TODAY...WITH A GRADUAL INCREASE IN CONVECTIVE COVERAGE AND A WELL-DEFINED SURFACE CIRCULATION EVIDENT IN VISIBLE SATELLITE IMAGERY. DVORAK CLASSIFICATIONS AT 18Z FROM BOTH TAFB AND SAB WERE T2.0...AND THE SYSTEM IS DESIGNATED A TROPICAL DEPRESSION WITH ESTIMATED MAXIMUM WINDS OF 30 KT. AS IS USUALLY THE CASE FOR EASTERN PACIFIC TROPICAL CYCLONES...THE FORWARD MOTION IS BEING DICTATED BY A SUBTROPICAL RIDGE OVER MEXICO...AND THE INITIAL MOTION ESTIMATE IS 290/14. WATER VAPOR IMAGERY DEPICTS A MID- TO UPPER-LEVEL TROUGH JUST OFF THE COAST OF CALIFORNIA. AS A RESULT...THE FORWARD SPEED OF THE DEPRESSION IS FORECAST TO SLOW DOWN A LITTLE DURING THE NEXT COUPLE OF DAYS AS IT APPROACHES A WEAKNESS IN THE RIDGE. BEYOND 48 HOURS...THE DYNAMICAL MODELS FORECAST THE WEST COAST TROUGH TO LIFT OUT AND ALLOW THE RIDGE TO BUILD WESTWARD A LITTLE OVER THE EASTERN PACIFIC...KEEPING THE TROPICAL CYCLONE ON A GENERAL WEST-NORTHWESTWARD HEADING. ONCE THE CYCLONE REACHES COOLER WATERS IN ABOUT THREE DAYS AND WEAKENS...IT SHOULD BECOME A MORE SHALLOW SYSTEM AND TURN WESTWARD WITH THE LOW-LEVEL FLOW. MODEL GUIDANCE IS IN GOOD AGREEMENT ON THIS GENERAL SCENARIO...AND THE OFFICIAL TRACK FORECAST IS JUST NORTH OF THE MODEL CONSENSUS. THE DEPRESSION IS CURRENTLY OVER SEA-SURFACE TEMPERATURES OF ABOUT 28 CELSIUS...AND THAT WILL REMAIN THE CASE FOR ABOUT THE NEXT 24 HOURS ALONG THE FORECAST TRACK...FOLLOWED BY STEADILY COOLER WATERS. MODERATE EASTERLY WIND SHEAR IS CURRENTLY AFFECTING THE CYCLONE...BUT MODELS FORECAST THE SHEAR TO WEAKEN A LITTLE AND REMAIN WEAK THROUGHOUT THE FIVE-DAY FORECAST PERIOD. AS A RESULT OF THESE CONDITIONS...A FAIRLY TYPICAL RISE AND FALL IN THE INTENSITY FOR AN EASTERN PACIFIC CYCLONE IS FORECAST. THE OFFICIAL FORECAST CALLS FOR A PEAK CLOSE TO HURRICANE INTENSITY IN A COUPLE OF DAYS...FOLLOWED BY A RAPID DECLINE OVER COOL WATERS...IN GENERAL AGREEMENT WITH BUT SLIGHTLY ABOVE THE SHIPS GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 06/2100Z 12.9N 111.8W 30 KT 12HR VT 07/0600Z 13.6N 113.8W 40 KT 24HR VT 07/1800Z 14.5N 116.1W 45 KT 36HR VT 08/0600Z 15.2N 118.1W 55 KT 48HR VT 08/1800Z 16.0N 120.2W 60 KT 72HR VT 09/1800Z 17.5N 124.5W 50 KT 96HR VT 10/1800Z 18.0N 128.5W 30 KT...REMNANT LOW 120HR VT 11/1800Z 18.0N 132.0W 20 KT...REMNANT LOW $$ FORECASTER KNABB NNNN
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