000 WTPZ43 KNHC 290854 TCDEP3 TROPICAL STORM JIMENA DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP132009 200 AM PDT SAT AUG 29 2009 ENHANCED INFRARED SATELLITE IMAGERY INDICATES THAT THE CENTER IS LIKELY EMBEDDED IN A SMALL MASS OF DEEP CONVECTION TO -80C...WITH A WELL-DEFINED CURVED BAND ARCING OUTWARD IN THE NORTHERN SEMICIRCLE. OVERALL...THE CLOUD PATTERN HAS EXHIBITED INCREASED ORGANIZATION DURING THE LAST SEVERAL HOURS. DVORAK T-NUMBERS OF T 2.5 AND T 3.0 FROM SAB AND TAFB...RESPECTIVELY. THEREFORE...THE DEPRESSION IS BEING UPGRADED TO TROPICAL STORM JIMENA WITH A 35 KT INITIAL INTENSITY. JIMENA CONTINUES TO MOVE ON A GENERAL WESTERLY COURSE...WITH A SOMEWHAT UNCERTAIN INITIAL MOTION ESTIMATE OF 280/10. MODEL GUIDANCE SHOWS A MID-LEVEL RIDGE COVERING CENTRAL/WESTERN MEXICO WHICH SHOULD STEER JIMENA ON A WESTWARD TO WEST-NORTHWESTWARD COURSE DURING THE NEXT 36-48 HOURS WITH SOME DECREASE IN FORWARD SPEED. THEREAFTER...GLOBAL MODELS DEPICT AN AMPLIFYING LONGWAVE TROUGH OVER THE EAST PACIFIC ALONG 135 WEST WHICH SHOULD CAUSE THE MID-LEVEL RIDGE OVER MEXICO TO SHIFT EASTWARD. THIS CHANGE IN THE STEERING FLOW SHOULD FORCE JIMENA TO MOVE ON A MORE NORTHWESTERLY COURSE BEYOND 48 HOURS. IT SHOULD BE NOTED THAT MODEL SPREAD IS RATHER LARGE TOWARD THE END OF THE FORECAST PERIOD...AS MODELS DIFFER ON THE STRENGTH OF SUBTROPICAL RIDGE TO THE NORTH OF THE CYCLONE. IN ONE CAMP...THE HWRF/GFDL CONTINUE TO FAVOR LESS RIDGING TO THE NORTH...RESULTING IN A TRACK RIGHT OF THE MODEL CONSENSUS. IN THE OTHER CAMP...THE UKMET/ECMWF/CANADIAN MODELS KEEP A MORE ROBUST RIDGE TO THE NORTH OF JIMENA AND THEREFORE TRACK THE CYCLONE MUCH FARTHER WEST. THE OFFICIAL FORECAST TRACK IS A COMPROMISE BETWEEN THE TWO EXTREMES...NEARLY IN BETWEEN THE PREVIOUS PACKAGE AND THE UPDATED MODEL CONSENSUS. JIMENA IS FORECAST TO ENCOUNTER A LIGHT SHEAR ENVIRONMENT AND VERY WARM SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK OVER THE NEXT FEW DAYS. THEREFORE...STRENGTHENING IS EXPECTED AND THE OFFICIAL FORECAST FOLLOWS THE MODEL CONSENSUS...CALLING FOR JIMENA TO BECOME A HURRICANE IN 36-48 HOURS. BY 96 HOURS...JIMENA SHOULD BE TRAVERSING COOLER WATERS...AND A GENERAL WEAKENING IS FORECAST. THE OFFICIAL INTENSITY FORECAST IS SLIGHTLY HIGHER THAN THE SHIPS MODEL GUIDANCE BUT LOWER THAN THE GFDL/HWRF RUNS WHICH MAKE JIMENA A MAJOR HURRICANE. FORECAST POSITIONS AND MAX WINDS INITIAL 29/0900Z 14.1N 102.3W 35 KT 12HR VT 29/1800Z 14.4N 103.5W 40 KT 24HR VT 30/0600Z 14.9N 104.8W 50 KT 36HR VT 30/1800Z 15.4N 106.1W 60 KT 48HR VT 31/0600Z 16.4N 107.3W 75 KT 72HR VT 01/0600Z 19.5N 110.0W 80 KT 96HR VT 02/0600Z 23.0N 112.5W 75 KT 120HR VT 03/0600Z 25.5N 114.0W 60 KT $$ FORECASTER KIMBERLAIN