000 WTPZ43 KNHC 200900 TCDEP3 TROPICAL DEPRESSION THIRTEEN-E DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132011 100 AM PST SUN NOV 20 2011 CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATE THE DEPRESSION HAS CHANGED LITTLE DURING THE PAST 6 HOURS. CONVECTION HAS BEEN WAXING AND WANING...AND THE LOW-LEVEL CENTER NOTED IN MICROWAVE IMAGERY IS LOCATED NEAR THE SOUTHWESTERN EDGE OF THE MAIN CONVECTIVE CLOUD MASS AND NOT IN THE COLD CLOUD SHIELD. ALSO...A 20/0350Z ASCAT PASS REVEALED THAT WINDS IN THE NORTHERN SEMICIRCLE HAD WEAKENED AND DECREASED IN AREAL COVERAGE COMPARED THE PREVIOUS OVERPASS JUST 12 HOURS EARLIER. BASED ON THIS INFORMATION AND A CONSENSUS T2.0/30 KT CLASSIFICATION FROM TAFB AND SAB...THE INITIAL INTENSITY IS BEING HELD AT 30 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 280/12 KT BASED ON MICROWAVE FIXES OVER THE PAST 12 HOURS. THE DEPRESSION IS MOVING ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE LOCATED FROM CENTRAL MEXICO AND EXTENDING WESTWARD ALONG 20N LATITUDE AND INTO THE CENTRAL PACIFIC OCEAN. THE EAST-WEST ORIENTATION AND STRENGTH OF THE RIDGE IS EXPECTED TO CHANGE LITTLE THROUGHOUT THE FORECAST PERIOD DESPITE A SERIES OF WEAK SHORTWAVE TROUGHS PASSING ACROSS BAJA CALIFORNIA...WHICH MAY ACT TO BRIEFLY WEAKEN THE RIDGE AND CREATE SOME MINOR STAIR-STEP MOTION IN THE TRACK. THE LATEST NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS GENERAL SCENARIO...AND THE OFFICIAL FORECAST TRACK IS A LITTLE SOUTH OF AND FASTER THAN THE PREVIOUS ADVISORY...AND IS NEAR THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE. VERTICAL SHEAR IS EXPECTED TO REMAIN LESS THAN 10 KT FOR THE NEXT 12-18 HOURS...WITH A GRADUAL INCREASE AROUND 15 KT FORECAST AFTER THAT. HOWEVER...THE SHEAR DIRECTION IS EXPECTED TO BE FROM THE EAST...WHICH IS A FAVORABLE DIRECTION FOR STRENGTHENING TO OCCUR. BY 48-72 HOURS...THE CYCLONE WILL BE MOVING INTO A REGION OF DRIER MID-LEVEL AIR AND ALSO OVER COOLER SSTS. THE RESULT IS THAT SLOW BUT STEADY STRENGTHENING IS FORECAST...ALTHOUGH THERE MAY BE SHARP FLUCTUATIONS IN THE INTENSIFICATION PROCESS AS THE VERTICAL SHEAR PULSES UP AND DOWN. AFTER 96 HOURS...THE CYCLONE WILL ENCOUNTER SUB-26C SEA SURFACE TEMPERATURES...WHICH SHOULD INDUCE GRADUAL WEAKENING. THE INTENSITY FORECAST IS IDENTICAL TO THE PREVIOUS ADVISORY FORECAST...AND IS SIMILAR TO A BLEND OF THE LGEM AND GFS MODELS...AND REMAINS WELL BELOW THE HWRF AND GFDL INTENSITY FORECASTS...ESPECIALLY AT 96 AND 120 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 10.4N 103.7W 30 KT 35 MPH 12H 20/1800Z 10.9N 105.5W 35 KT 40 MPH 24H 21/0600Z 11.4N 107.9W 40 KT 45 MPH 36H 21/1800Z 11.6N 110.1W 50 KT 60 MPH 48H 22/0600Z 11.8N 112.3W 55 KT 65 MPH 72H 23/0600Z 11.9N 116.4W 65 KT 75 MPH 96H 24/0600Z 12.6N 120.7W 70 KT 80 MPH 120H 25/0600Z 13.5N 124.6W 55 KT 65 MPH $$ FORECASTER STEWART