000 WTPZ44 KNHC 130834 TCDEP4 TROPICAL STORM CARLOS DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP042009 200 AM PDT MON JUL 13 2009 CARLOS CONSISTS OF AN AMORPHOUS BLOB OF DEEP CONVECTION WITH A FEW POORLY-DEFINED BANDING FEATURES OVER THE SOUTHERN AND WESTERN PORTIONS OF THE CIRCULATION. ITS RECENT APPEARANCE REPRESENTS A DECREASE IN ORGANIZATION...AND SUBJECTIVE DVORAK T-NUMBERS OF 2.5 AND 3.0 FROM SAB AND TAFB...RESPECTIVELY...REFLECT A GRADUAL WEAKENING. THEREFORE THE INITIAL INTENSITY IS LOWERED TO 45 KT...WITHIN THE REALM OF AVAILABLE ESTIMATES. THE WEAKENING OF CARLOS OBSERVED DURING THE PAST 24 HOURS HAS INDEED BEEN PUZZLING...AND THUS THE INTENSITY FORECAST IS OF LOW CONFIDENCE. CARLOS HAS WELL-DEFINED UPPER-LEVEL OUTFLOW...AND IS IN AN ENVIRONMENT OF LOW VERTICAL WIND SHEAR AND RELATIVELY WARM SEA SURFACE TEMPERATURES. ALL OF THESE FACTORS SHOULD FAVOR INTENSIFICATION...YET THE CYCLONE HAS WEAKENED 30 KT SINCE THIS TIME YESTERDAY. THIS IS ANOTHER EXAMPLE OF OUR LACK OF UNDERSTANDING OF TROPICAL CYCLONE INTENSITY CHANGE. NO MATTER THE INEXPLICABLE WEAKENING...THE GFDL AND GFDN MODELS PREDICT THAT CARLOS WILL REACQUIRE HURRICANE STATUS...WHILE SHIPS INDICATES LITTLE FURTHER DEVELOPMENT...AND THE HWRF WEAKENS CARLOS TO A TROPICAL DEPRESSION. GIVEN RECENT TRENDS AND THE LESS BULLISH NUMERICAL GUIDANCE...THE OFFICIAL FORECAST WILL CALL FOR ONLY MODEST STRENGTHENING EVEN THOUGH ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE FOR THE NEXT 2 TO 3 DAYS. THEREAFTER...A SUBTLE INCREASE IN WESTERLY FLOW ALOFT AND SLIGHTLY COOLER WATERS SHOULD RESULT IN WEAKENING. THE INITIAL MOTION ESTIMATE IS 270/11. THE NOGAPS AND GFDN MODELS REMAIN NORTHERN OUTLIERS...AND ARE DISCOUNTED AS MOST DYNAMICAL GUIDANCE INDICATES THE MID-LEVEL SUBTROPICAL RIDGE REMAINING WELL-ESTABLISHED TO THE NORTH OF CARLOS THROUGH THE FORECAST PERIOD. ESSENTIALLY...THE NEW OFFICIAL FORECAST IS AN UPDATE OF THE PREVIOUS ADVISORY BUT IS FARTHER SOUTH THAN THE MODEL CONSENSUS...SINCE THE LATTER INCLUDES THE QUESTIONABLE NOGAPS AND GFDN SOLUTIONS. FORECAST POSITIONS AND MAX WINDS INITIAL 13/0900Z 10.2N 124.1W 45 KT 12HR VT 13/1800Z 10.2N 125.8W 50 KT 24HR VT 14/0600Z 10.4N 128.0W 50 KT 36HR VT 14/1800Z 10.7N 130.2W 55 KT 48HR VT 15/0600Z 11.1N 132.3W 55 KT 72HR VT 16/0600Z 11.9N 136.4W 55 KT 96HR VT 17/0600Z 12.5N 141.0W 50 KT 120HR VT 18/0600Z 12.5N 145.5W 45 KT $$ FORECASTER KIMBERLAIN/PASCH