000 WTPZ43 KNHC 100236 TCDEP3 TROPICAL STORM LOWELL DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP132008 800 PM PDT TUE SEP 09 2008 INTERMITTENT BURSTS OF MODERATE CONVECTION HAVE CONTINUE TO FORM IN THE WESTERN SEMICIRCLE...WHILE THE ASSOCIATED CIRRUS CANOPY HAS SPREAD EASTWARD AND HAS OBSCURED THE LOW-LEVEL CENTER. SATELLITE CURRENT INTENSITY ESTIMATES ARE T2.5/35 KT FROM BOTH TAFB AND SAB...BUT DATA T-NUMBERS ARE T2.0/30 KT. HOWEVER...LOW-CLOUD ELEMENTS IN THE EASTERN SEMICIRCLE HAVE BEEN MOVING AT 35-40 KT... SO THE INTENSITY IS BEING HELD AT 40 KT FOR THIS ADVISORY BASED ON THE ASSUMPTION THAT SLIGHTLY STRONGER WINDS EXIST WITHIN THE CONVECTION ON THE WEST SIDE OF THE LOW-LEVEL CENTER. THE MOTION ESTIMATE IS NOW 015/05. IT APPEARS THAT LOWELL IS NOW PASSING ALONG OR JUST NORTH OF THE SUBTROPICAL RIDGE AXIS AND WATER VAPOR IMAGERY INDICATES A BROAD MID-LATITUDE TROUGH TO THE NORTH CONTINUES TO DROP SLOWLY SOUTHWARD. SOUTHWESTERLY UPPER-LEVEL WINDS ARE BEGINNING TO IMPINGE ON THE WEST SIDE OF THE WEAK OUTFLOW PATTERN...WHICH MEANS THAT GRADUAL RECURVATURE TO THE NORTHEAST SHOULD BEGIN WITHIN THE NEXT 12 HOURS. THE NHC MODEL GUIDANCE IS TIGHTLY CLUSTERED ABOUT THE PREVIOUS FORECAST TRACK ACROSS SOUTHERN BAJA CALIFORNIA IN 24-36 HOURS...SO NO SIGNIFICANT CHANGES HAVE BEEN MADE TO THE PREVIOUS ADVISORY. LOWELL HAS BEEN INGESTING COOLER AND MORE STABLE AIR INTO THE CIRCULATION...WHICH HAS BEEN INHIBITING CONVECTIVE DEVELOPMENT. THE CYCLONE IS ALSO PASSING OVER THE COOLEST WATER ALONG THE FORECAST TRACK. VERTICAL SHEAR IS LOW AND IS EXPECTED TO REMAIN THAT WAY UNTIL LANDFALL OCCURS OVER SOUTHERN BAJA CALIFORNIA. SINCE LOWELL WILL BE MOVING RELATIVELY SLOWLY OVER SSTS THAT INCREASE TO NEAR 28C...SOME ADDITIONAL CONVECTION MAY DEVELOP BEFORE LANDFALL OCCURS...AND FOR THIS REASON THE INTENSITY IS BEING MAINTAINED AT 35 KT FOR THE NEXT 24-30 HOURS. THE OFFICIAL INTENSITY FORECAST IS IDENTICAL TO THE PREVIOUS ADVISORY AND IS SLIGHTLY LOWER THAN THE SHIPS INTENSITY MODEL FORECAST. FORECAST POSITIONS AND MAX WINDS INITIAL 10/0300Z 21.3N 113.1W 40 KT 12HR VT 10/1200Z 22.2N 112.6W 35 KT 24HR VT 11/0000Z 23.3N 111.8W 35 KT 36HR VT 11/1200Z 24.4N 110.9W 30 KT...INLAND OVER BAJA 48HR VT 12/0000Z 25.9N 110.2W 25 KT...OVER GULF OF CALIF 72HR VT 13/0000Z 27.3N 109.9W 20 KT...INLAND OVER MEXICO 96HR VT 14/0000Z...DISSIPATED $$ FORECASTER STEWART