000 WTPZ43 KNHC 072048 TCDEP3 TROPICAL STORM LOWELL DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP132008 200 PM PDT SUN SEP 07 2008 ALL OF THE LOWELL'S DEEP CONVECTION REMAINS ON THE SOUTHWEST SIDE OF ITS CENTER DUE TO PERSISTENT NORTHEASTERLY WIND SHEAR. THE CENTER IS ALSO PARTIALLY EXPOSED...REVEALING A COMPLEX PATTERN OF MESOVORTICES WITHIN THE LARGER CIRCULATION. A QUIKSCAT PASS FROM EARLIER SUGGESTS THE MAXIMUM WINDS WERE ABOUT 45 KT...SO THIS VALUE WILL BE USED AS THE INITIAL INTENSITY. ALTHOUGH GLOBAL MODELS FORECAST A MORE FAVORABLE UPPER ENVIRONMENT FOR STRENGTHENING IN A DAY OR SO...NONE OF THE DYNAMICAL OR STATISTICAL MODELS FORECAST MUCH STRENGTHENING. GIVEN THAT LOWELL SHOULD BE OVER RELATIVELY WARM WATER AND LIGHT SHEAR FOR AT LEAST 48 HR...I'M GOING TO REDUCE THE NHC FORECAST ONLY SLIGHTLY FROM THE PREVIOUS ONE...BUT NOT AS MUCH AS MOST OF THE MODEL GUIDANCE. A COMBINATION OF COOLER SSTS AND ENTRAINMENT OF DRIER AIR FROM THE NORTHWEST SHOULD WEAKEN THE STORM IN THE LONG-TERM. VISIBLE SATELLITE IMAGERY IS GIVING A BETTER IDEA OF THE INITIAL MOTION...NOW 305/10. THERE IS NO CHANGE TO THE SYNOPTIC REASONING. A GENERAL NORTHWESTWARD TRACK IS EXPECTED AS LONG AS THE LOWELL REMAINS ON THE SOUTHWEST SIDE OF A SUBTROPICAL RIDGE OVER MEXICO. A WEAKNESS IN THE RIDGE SHOULD DEVELOP IN TWO OR THREE DAYS AS A TROUGH MOVES DOWN THE WEST COAST OF THE USA...STEERING THE STORM TOWARD THE NORTH AND EVENTUALLY NORTHEAST. THERE IS STILL SOME SPREAD OF WHEN THE TURN BACK TOWARD BAJA OCCURS. HOWEVER ALL RELIABLE MODELS EXCEPT THE NOGAPS NOW TURN THE SYSTEM TO THE NORTHEAST OR EAST BY THE END OF THE FORECAST. THE OFFICIAL FORECAST IS SHIFTED TO THE EAST...BUT IS STILL WEST OF THE MODEL CONSENSUS. IT WOULD NOT BE SURPRISING IF THE NEXT FORECAST WAS ADJUSTED EVEN FARTHER NORTHEAST. FORECAST POSITIONS AND MAX WINDS INITIAL 07/2100Z 17.9N 108.8W 45 KT 12HR VT 08/0600Z 18.7N 110.0W 45 KT 24HR VT 08/1800Z 19.6N 111.3W 50 KT 36HR VT 09/0600Z 20.4N 112.4W 50 KT 48HR VT 09/1800Z 21.0N 113.2W 50 KT 72HR VT 10/1800Z 22.0N 113.5W 50 KT 96HR VT 11/1800Z 23.0N 112.5W 45 KT 120HR VT 12/1800Z 23.5N 111.5W 35 KT $$ FORECASTER BLAKE