000 WTPZ43 KNHC 080228 TCDEP3 TROPICAL STORM LOWELL DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP132008 800 PM PDT SUN SEP 07 2008 ALTHOUGH LOWELL HAS BEEN EXPERIENCING MODERATE EASTERLY SHEAR...DEEP CONVECTION HAS CONTINUED TO INCREASE AND NOW COMPLETELY COVERS THE PREVIOUSLY EXPOSED LOW-LEVEL CENTER. THE DVORAK INTENSITY ESTIMATE AT 00Z FROM BOTH TAFB AND SAB WAS T3.0/45 KT. HOWEVER...DURING THE PAST 2 HOURS SINCE THAT SATELLITE FIX...DATA T-NUMBERS HAVE INCREASED TO T3.5/55 KT AS THE CENTER HAS BECOME EMBEDDED FARTHER INTO THE EASTERN PORTION OF THE CONVECTIVE CLOUD MASS. THEREFORE ...THE INITIAL INTENSITY IS INCREASED TO 50 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 295/10. LOWELL HAS MADE A SLIGHT WESTWARD JOG PROBABLY IN RESPONSE TO THE DEVELOPMENT OF THE DEEP CONVECTION OVER THE CENTER...WHICH HAS VERTICALLY INCREASED THE VORTEX UP TO THE 200 MB LEVEL WHERE MODERATE EASTERLY WINDS EXIST. OTHER THAN THIS SHORT TERM WOBBLE TO THE LEFT OF THE PREVIOUS TRACK ...THE PREVIOUS FORECAST TRACK AND REASONING REMAINS UNCHANGED. ALL OF THE GLOBAL MODELS AGREE THAT AN UPPER-LEVEL TROUGH/LOW CURRENTLY OVER NORTHERN CALIFORNIA WILL DIG SOUTHWARD AND ERODE THE MID-/UPPER-LEVEL RIDGE TO THE NORTH OF LOWELL BY 48-72 HOURS. THIS IS EXPECTED TO WEAKEN THE STEERING FLOW AND PERMIT LOWELL TO SLOWLY RECURVE TO THE NORTHEAST TOWARD SOUTHERN BAJA CALIFORNIA. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK AND IS A LITTLE TO THE LEFT...OR WEST...OF THE NHC MODEL CONSENSUS. THE VERTICAL SHEAR ACROSS LOWELL IS FORECAST TO GRADUALLY WEAKEN TO LESS THAN 10 KT BY 36 HOURS...WHILE REMAINING OVER SSTS OF AT LEAST 27C. THE MID-LEVEL ENVIRONMENT IS ALSO FORECAST TO REMAIN QUITE MOIST WITH RELATIVE HUMIDITY VALUES OF MORE THAN 70 PERCENT. THESE CONDITIONS WOULD TYPICALLY INDICATE THAT SOME DEGREE OF STRENGTHENING IS LIKELY. HOWEVER...THE SHIPS MODEL STEADILY DECREASES LOWELL'S INTENSITY AND MAKES THE CYCLONE A DEPRESSION BY 96 HOURS. GIVEN THE FAVORABLE CONDITIONS DESCRIBED ABOVE...THE OFFICIAL INTENSITY FORECAST IS HELD HIGHER THAN THE SHIPS MODEL AND IS SIMILAR TO THE HWRF MODEL...WHICH MAKES LOWELL A CATEGORY 1 HURRICANE BY 24 HOURS BEFORE SLOWLY WEAKENING IT. FORECAST POSITIONS AND MAX WINDS INITIAL 08/0300Z 18.2N 109.8W 50 KT 12HR VT 08/1200Z 18.9N 110.9W 55 KT 24HR VT 09/0000Z 19.9N 112.3W 55 KT 36HR VT 09/1200Z 20.7N 113.3W 60 KT 48HR VT 10/0000Z 21.6N 113.7W 60 KT 72HR VT 11/0000Z 22.8N 113.3W 55 KT 96HR VT 12/0000Z 24.0N 112.0W 50 KT...NEAR SOUTHWEST BAJA 120HR VT 13/0000Z 25.0N 110.5W 35 KT...OVR SRN GULF OF CALIF $$ FORECASTER STEWART