ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM HERNAN DISCUSSION NUMBER 24 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008 800 AM PDT TUE AUG 12 2008 HERNAN HAS VERY LITTLE DEEP CONVECTION NOW THAT IT IS OVER SEA SURFACE TEMPERATURES NEAR 23C. AN AVERAGE OF THE TAFB AND SAB SATELLITE CLASSIFICATIONS PROVIDES AN ESTIMATE OF 45 KT AND THE MOST RECENT ADT IS NOW DOWN TO 30 KT. GIVEN THE DEGRADATION OF THE CLOUD PATTERN...THE INITIAL INTENSITY IS SET AS 40 KT AS A COMPROMISE OF THE SUBJECTIVE AND OBJECTIVE TECHNIQUES. SINCE IT IS UNLIKELY THAT HERNAN WILL BE ABLE TO GENERATE PERSISTENT CONVECTION OVER THE COOLER WATERS...THE CYCLONE IS EXPECTED TO WEAKEN TO A TROPICAL DEPRESSION LATER TODAY. THE NEW FORECAST SHOWS HERNAN DISSIPATING INTO AN OPEN WAVE WITHIN THE TRADE WIND BELT SOUTHEAST OF HAWAII BY DAY 5...IF NOT SOONER...IN LINE WITH THE GLOBAL MODEL GUIDANCE. THE INITIAL MOTION IS JUST SOUTH OF DUE WEST AT 260/8. THE SHORT-TERM MOTION WILL BE DICTATED BY A MID-LEVEL RIDGE AXIS EXTENDING SOUTHWEST OF SOUTHERN CALIFORNIA DIRECTLY TOWARDS HERNAN...WHICH WILL FORCE A MORE WEST-SOUTHWESTWARD MOTION. ONCE HERNAN WEAKENS TO A REMNANT LOW...IT IS EXPECTED TO TURN WEST WITH AN INCREASE IN SPEED AS IT IS STEERED BY THE LOW-LEVEL SUBTROPICAL RIDGE. FORECAST POSITIONS AND MAX WINDS INITIAL 12/1500Z 18.3N 133.6W 40 KT 12HR VT 13/0000Z 18.1N 134.7W 30 KT 24HR VT 13/1200Z 17.7N 136.2W 30 KT 36HR VT 14/0000Z 17.2N 137.7W 25 KT...REMNANT LOW 48HR VT 14/1200Z 16.7N 139.2W 25 KT...REMNANT LOW 72HR VT 15/1200Z 15.5N 143.5W 20 KT...REMNANT LOW 96HR VT 16/1200Z 15.0N 148.0W 20 KT...REMNANT LOW 120HR VT 17/1200Z...DISSIPATED $$ FORECASTER BERG/BROWN NNNN
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