000 WTPZ43 KNHC 081446 TCDEP3 TROPICAL STORM LOWELL DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP132008 800 AM PDT MON SEP 08 2008 MORNING VISIBLE SATELLITE IMAGERY AND A RECENT TRMM MICROWAVE OVERPASS SHOW THAT THE CENTER OF LOWELL REMAINS EXPOSED TO THE NORTHEAST OF A CONVECTIVE BURST. ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE THAT THE STORM IS UNDERGOING ABOUT 20 KT OF EASTERLY VERTICAL WIND SHEAR. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 35 AND 45 KT RESPECTIVELY. IN ADDITION...JUST-RECEIVED QUIKSCAT DATA SHOW 40 KT WINDS...AND THERE WAS AN AMSU INTENSITY ESTIMATES OF 43 KT AT 0926Z. BASED ON THE ABOVE...THE INITIAL INTENSITY IS REDUCED TO 45 KT. THE INITIAL MOTION IS 305/8. LOWELL IS CURRENTLY BEING STEERED BY A MID-LEVEL RIDGE OVER NORTHERN MEXICO. ALL OF THE DYNAMICAL MODELS FORECAST A MID/UPPER-LEVEL TROUGH TO AMPLIFY SOUTHWARD ALONG THE WEST COAST OF THE UNITED STATES DURING THE NEXT COUPLE OF DAYS...WHICH 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...BAMD...AND LBAR ALL MOVE THE THE STORM VERY RAPIDLY... WITH 120 HR POSITIONS OVER THE CENTRAL UNITED STATES. ON THE OTHER HAND...THE GFS...UKMET...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 STRIKING AND SUGGESTS THE POSSIBILITY THAT LOWELL COULD SHEAR APART AFTER 48 HR. THE NEW FORECAST TRACK IS A LITTLE FASTER THAN THE SLOWEST MODELS...CALLING FOR LOWELL TO REACH BAJA CALIFORNIA IN ABOUT 4 DAYS AND THEN MOVE INTO THE GULF OF CALIFORNIA. IT IS A LITTLE TO THE RIGHT OF THE PREVIOUS TRACK BASED ON THE INITIAL POSITION AND MOTION...AND IT IS IN THE BEST AGREEMENT WITH THE GFDL AND ECMWF. 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 SHOULD REDUCE THE CHANCE OF INTENSIFICATION EVEN WHEN THE SHEAR DECREASES. AFTER RECURVATURE...LOWELL MAY FIND WARMER WATER...BUT IS ALSO EXPECTED TO ENCOUNTER INCREASING SOUTHWESTERLY SHEAR.. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A SLOW WEAKENING DURING THE FORECAST PERIOD. THUS...THE NEW INTENSITY FORECAST ALSO CALLS FOR A GRADUAL WEAKENING...WITH THE NEW INTENSITIES 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 08/1500Z 19.0N 111.2W 45 KT 12HR VT 09/0000Z 19.8N 112.0W 45 KT 24HR VT 09/1200Z 20.7N 113.0W 45 KT 36HR VT 10/0000Z 21.5N 113.5W 40 KT 48HR VT 10/1200Z 22.4N 113.5W 40 KT 72HR VT 11/1200Z 23.5N 112.5W 35 KT 96HR VT 12/1200Z 25.0N 111.0W 30 KT...INLAND 120HR VT 13/1200Z 26.0N 110.0W 30 KT $$ FORECASTER BEVEN