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| #377979 (Received by flhurricane at: 10:41 AM 22.Sep.2010) TCDAT4 TROPICAL STORM LISA DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL142010 1100 AM EDT WED SEP 22 2010 LISA IS PRODUCING A SMALL AREA OF DEEP CONVECTION NEAR THE SURFACE CENTER...BUT MUCH OF THE LOW-LEVEL CIRCULATION IS EXPOSED AROUND THE CONVECTIVE MASS. DVORAK CURRENT INTENSITY ESTIMATES ARE 3.0/45 KT AND 2.5/35 KT FROM TAFB AND SAB...SO THE INITIAL INTENSITY IS BEING MAINTAINED AT 40 KT. A FEW MICROWAVE PASSES...PARTICULARLY A 0919 UTC SSMIS PASS...INDICATED THAT THE CENTER OF LISA HAS DRIFTED SOUTHEASTWARD OVERNIGHT AND IS NOW LOCATED JUST A LITTLE FARTHER SOUTH THAN PREVIOUSLY ESTIMATED. THE BEST ESTIMATE OF THE INITIAL MOTION IS 125 DEGREES AT 3 KT. LISA IS EXPECTED TO MOVE VERY LITTLE DURING THE NEXT 48 HOURS AS IT REMAINS TRAPPED IN A MID-LEVEL COL REGION BETWEEN A RIDGE TO THE EAST OVER AFRICA...A RIDGE TO THE WEST OVER THE CENTRAL ATLANTIC...AND A SHARP TROUGH TO THE NORTH BETWEEN THE AZORES AND CANARY ISLANDS. AFTER 48 HOURS...THE TROUGH IS EXPECTED TO LIFT NORTHEASTWARD TOWARDS EUROPE AND THE AFRICAN RIDGE WILL THEN BUILD WESTWARD...NUDGING LISA A LITTLE FARTHER WEST OVER THE ATLANTIC. THE TRACK GUIDANCE IS IN AGREEMENT ON THIS SCENARIO... AND THE NHC FORECAST IS VERY CLOSE TO THE MODEL CONSENSUS TVCN AND THE PREVIOUS FORECAST. THE STRONGEST UPPER-LEVEL WINDS ARE LOCATED JUST NORTH OF THE CYCLONE. SINCE THE STORM IS LOCATED WITHIN THE COL...THE SHEAR DIRECTLY OVER THE CENTER IS RATHER LOW AT THIS TIME. HOWEVER... THERE IS A LOT OF MID-LEVEL DRY AIR AROUND LISA...AND THAT COULD BE WHAT IS PREVENTING INTENSIFICATION. SOME STRENGTHENING IS STILL POSSIBLE DURING THE NEXT 48 HOURS WHILE THE SHEAR REMAINS RELATIVELY LOW...BUT INCREASING SHEAR AFTER THAT TIME SHOULD CAUSE WEAKENING. THERE IS GREATER SPREAD IN THE INTENSITY GUIDANCE AFTER 48 HOURS. THE OFFICIAL INTENSITY FORECAST...WHICH HAS AGAIN BEEN LOWERED A BIT FROM THE PREVIOUS FORECAST...IS CLOSE TO THE MODEL CONSENSUS DURING THAT TIME. FORECAST POSITIONS AND MAX WINDS INITIAL 22/1500Z 17.1N 30.5W 40 KT 12HR VT 23/0000Z 17.1N 30.3W 40 KT 24HR VT 23/1200Z 17.0N 30.3W 45 KT 36HR VT 24/0000Z 17.0N 30.7W 45 KT 48HR VT 24/1200Z 17.3N 31.3W 50 KT 72HR VT 25/1200Z 18.5N 33.0W 50 KT 96HR VT 26/1200Z 20.0N 35.0W 45 KT 120HR VT 27/1200Z 21.5N 38.5W 35 KT $$ FORECASTER BERG |
