000 WTPZ43 KNHC 082039 TCDEP3 TROPICAL STORM LOWELL DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP132008 200 PM PDT MON SEP 08 2008 LOWELL CONTINUES TO EXPERIENCE ABOUT 20 KT OF EASTERLY VERTICAL WIND SHEAR...WHICH IS CAUSING THE LOW-LEVEL CENTER TO BE PARTLY EXPOSED AT THE NORTHEASTERN EDGE OF A PULSING AND PERSISTENT CONVECTIVE MASS. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM SAB AND 35 KT FROM TAFB....WHILE A QUIKSCAT OVERPASS THIS MORNING SHOWED ONE 45 KT WIND. THE INITIAL INTENSITY IS HELD AT 45 KT...AND RECENTLY RECEIVED LOW-RESOLUTION ASCAT DATA SUGGESTS THIS MAY BE GENEROUS. THE INITIAL MOTION IS NOW 315/10. THERE IS LITTLE CHANGE TO THE EARLIER FORECAST PHILOSOPHY. LOWELL IS CURRENTLY BEING STEERED BY A MID-LEVEL RIDGE OVER NORTHERN MEXICO. ALL OF THE DYNAMICAL MODELS FORECAST A MID/UPPER-LEVEL TROUGH...CURRENTLY SEEN DEVELOPING IN WATER VAPOR IMAGERY...TO AMPLIFY SOUTHWARD ALONG THE WEST COAST OF THE UNITED STATES DURING THE NEXT COUPLE OF DAYS. THIS SHOULD TURN LOWELL TOWARD THE NORTH AND EVENTUALLY NORTHEAST. WHILE THE GUIDANCE AGREES ON THIS SCENARIO...THERE IS MAJOR DISAGREEMENT ON HOW FAST LOWELL WILL MOVE AFTER RECURVATURE. THE HWRF...LBAR...AND BAMD MOVE THE STORM VERY RAPIDLY...WITH 120 HR POSITIONS OVER THE CENTRAL UNITED STATES. ON THE OTHER HAND...THE GFS AND BAMS KEEP THE LOW-LEVEL CENTER WEST AND SOUTHWEST OF BAJA CALIFORNIA THROUGH 120 HR. THE DIFFERENCE BETWEEN THE BAMS AND BAMD MODELS IS STILL STRIKING AND SUGGESTS THE POSSIBILITY THAT LOWELL COULD SHEAR APART AFTER 48 HR. THE NEW FORECAST TRACK IS A SLOW-MOTION COMPROMISE BETWEEN THESE EXTREMES...SHOWING LOWELL SLOWLY RECURVING TO THE NORTHEAST AND REACHING THE SOUTHERN BAJA PENINSULA IN 72-96 HR. THE FORECAST TRACK IS A LITTLE SLOWER THAN THE OVERALL MODEL CONSENSUS AND IN BEST AGREEMENT WITH THE GUNA CONSENSUS MODEL AND THE FLORIDA STATE SUPERENSEMBLE. AS BEFORE...THE DYNAMICAL MODELS FORECAST THE CURRENT SHEAR TO DIMINISH IN ABOUT 24 HOUR. HOWEVER...LOWELL IS FORECAST TO MOVE TOWARD COOLER SEA SURFACE TEMPERATURES DURING THE NEXT 48 HR...AND THIS REDUCES THE CHANCE OF INTENSIFICATION WHEN THE SHEAR DECREASES. AFTER RECURVATURE...LOWELL MAY FIND WARMER WATER...BUT IS ALSO EXPECTED TO ENCOUNTER INCREASING SOUTHERLY AND SOUTHWESTERLY SHEAR. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A SLOW WEAKENING DURING THE FORECAST PERIOD. THE INTENSITY FORECAST AGAIN CALLS FOR A GRADUAL WEAKENING ...WITH THE INTENSITIES HELD A LITTLE ABOVE ALL THE GUIDANCE. AN ALTERNATIVE SCENARIO WOULD BE FOR LOWELL TO SHEAR APART AFTER 48 HR...WHICH WOULD LEAD TO DISSIPATION BEFORE THE END OF THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INITIAL 08/2100Z 19.8N 112.1W 45 KT 12HR VT 09/0600Z 20.4N 112.7W 45 KT 24HR VT 09/1800Z 21.2N 113.4W 40 KT 36HR VT 10/0600Z 22.1N 113.5W 40 KT 48HR VT 10/1800Z 23.1N 113.1W 35 KT 72HR VT 11/1800Z 24.5N 112.0W 35 KT...NEAR BAJA COAST 96HR VT 12/1800Z 25.5N 111.0W 30 KT...INLAND 120HR VT 13/1800Z 26.5N 110.0W 30 KT...OVER WATER $$ FORECASTER BEVEN