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| #542073 (Received by flhurricane at: 10:41 AM 11.Sep.2012) TCDAT4 TROPICAL DEPRESSION FOURTEEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 AM AST TUE SEP 11 2012 ALTHOUGH THERE IS NOT MUCH DEEP CONVECTION NEAR THE CENTER OF CIRCULATION OF THE LOW PRESSURE SYSTEM OVER THE CENTRAL TROPICAL ATLANTIC...AN OUTER CONVECTIVE BAND TO THE WEST OF THE CENTER HAS CONTINUED TO BECOME BETTER ORGANIZED. DVORAK ESTIMATES HAVE RISEN TO T2.5 FROM TAFB AND T2.0 FROM SAB...SUPPORTING THE DESIGNATION OF THIS SYSTEM AS A TROPICAL DEPRESSION. THE INITIAL MOTION IS ESTIMATED TO BE WESTWARD...OR 275/9 KT. THE DEPRESSION SHOULD BE TURNING WEST-NORTHWESTWARD VERY SOON AS IT MOVES ALONG THE SOUTHWESTERN EDGE OF THE SUBTROPICAL RIDGE...WHICH CURRENTLY EXTENDS FROM AFRICA WESTWARD TO 50W. THE RIDGE IS EXPECTED TO WEAKEN OVER THE NEXT 5 DAYS WHILE BEING ERODED BY A LARGE MID-/UPPER-LEVEL LOW THAT WILL BE DROPPING SOUTH OF THE AZORES...AND THE DEPRESSION SHOULD RESPOND BY TURNING NORTHWARD BY DAY 4 AND NORTHEASTWARD BY DAY 5. THE TRACK GUIDANCE IS IN GOOD AGREEMENT UNTIL ABOUT 72 HOURS WHEN THE ECMWF MODEL BEGINS TO LAG BEHIND THE OTHER MODELS...BUT THIS IS COMPENSATED FOR IN THE MODEL CONSENSUS BY THE FASTER GFDL AND HWRF MODELS. THE OFFICIAL NHC FORECAST INDICATES A TRACK LEANING TOWARDS THE SLOWER SCENARIO... AND IS VERY CLOSE TO THE GFS SOLUTION. SATELLITE IMAGERY INDICATES THAT THE DEPRESSION IS BORDERED BY DRY SAHARAN AIR TO ITS NORTH AND WEST...BUT THE CYCLONE IS ALSO DRAWING IN MOIST AIR FROM THE SOUTH. SINCE DEEP CONVECTION NEAR THE CENTER IS SCANT...IT MIGHT TAKE SOME TIME FOR THE DEPRESSION TO STRENGTHEN UNTIL IT CAN MIX OUT SOME OF THE DRY AIR. SHEAR IS EXPECTED TO BE LOW FOR THE NEXT 3 DAYS OR SO...AND STRENGTHENING IS INDICATED IN THE OFFICIAL FORECAST UP TO THAT TIME. STRENGTHENING COULD BE ARRESTED IN 4-5 DAYS WHEN THE CYCLONE BEGINS TO ENCOUNTER WESTERLY SHEAR. THERE IS SOME SIGNIFICANT SPREAD IN THE INTENSITY MODELS AT THE LATTER END OF THE FORECAST PERIOD...WITH THE SHIPS AND LGEM MODELS BEING 20-25 KT DIFFERENT FROM EACH OTHER. SINCE THE LGEM MODEL...WHICH IS THE LOWER OF THE TWO...IS DESIGNED TO BETTER HANDLE CHANGES IN THE SHEAR AT THE LONGER FORECAST TIMES... IT IS POSSIBLE THAT THE CYCLONE COULD BE WEAKER THAN INDICATED IN THE FORECAST ON DAYS 4 AND 5. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 16.3N 43.1W 30 KT 35 MPH 12H 12/0000Z 17.0N 44.5W 35 KT 40 MPH 24H 12/1200Z 18.3N 46.8W 40 KT 45 MPH 36H 13/0000Z 19.8N 49.3W 50 KT 60 MPH 48H 13/1200Z 21.4N 51.3W 60 KT 70 MPH 72H 14/1200Z 25.0N 54.0W 65 KT 75 MPH 96H 15/1200Z 28.5N 53.5W 65 KT 75 MPH 120H 16/1200Z 30.5N 51.0W 65 KT 75 MPH $$ FORECASTER BERG |
