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| #38719 (Received by flhurricane at: 10:40 AM 10.Aug.2005) TCDAT4 TROPICAL DEPRESSION IRENE DISCUSSION NUMBER 24 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT WED AUG 10 2005 THE CONVECTIVE CLOUD PATTERN THIS MORNING HAS IMPROVED SIGNIFICANTLY COMPARED TO 24 HOURS AGO. IT IS STILL DIFFICULT...HOWEVER...TO DETERMINE AN EXACT CENTER LCOATION...ESPECIALLY IN CONVENTIONAL IMAGERY. THE INITIAL POSITION IS BASED ON CONTINUITY...A 24-HOUR WESTWARD MOTION...AND TRMM AND MICROWAVE SATELLITE DATA. A 0912Z QUIKSCAT PASS INTIMATED THAT A LOW-LEVEL CENTER COULD BE FARTHER SOUTH NEAR 21N...BUT I PREFER TO REMAIN FARTHER NORTH NEAR THE BETTER DEFINED MID-LEVEL CIRCULATION...WHICH ALSO ALLOWS FOR SOME POSSIBLE REDEVELOPMENT FARTHER NORTH. THE INITIAL MOTION ESTIMATE IS 275/10...EVEN THOUGH THE LONGER TERM MOTION HAS BEEN 270/08. GLOBAL MODEL GUIDANCE HAS CONSISTENTLY DISPLAYED A 20-30 DEGREE RIGHT-OF-TRACK BIAS THE PAST 48 HOURS. THIS IS NOT SURPRISING SINCE THE MODELS HAVE KEPT IRENE WEAK OR HAVE EVEN DISSIPATED IT...ALL THE WHILE MID-LEVEL NORTHERLY FLOW HAS BEEN KEEPING THE CYCLONE FARTHER SOUTH ON A MORE WESTWARD TRACK. WATER VAPOR IMAGERY AND SATELLITE-DERIVED WINDS FROM UW-CIMSS STILL INDICATE A LARGE MID- TO UPPER-LEVEL ANTICYCLONE LOCATED FROM THE SOUTHEASTERN U.S. EASTWARD ACROSS BERMUDA WITH DEEP NORTH TO NORTHEASTERLY MID-LEVEL FLOW ON THE EAST SIDE UNDERCUTTING THE IMPROVING UPPER-LEVEL OUTFLOW PATTERN. SO IN THE SHORT TERM...A MORE WESTWARD COMPONENT OF MOTION IS PROBABLE... BARRING ANY NORTHWARD REDEVELOPMENT OF THE LOW-LEVEL CENTER. BY DAYS 4-5...MOST OF THE GLOBAL MODELS CREATE A WEAKNESS IN THE SUBTROPICAL RIDGE OFF THE SOUTHEASTERN U.S. COAST...WITH A HIGH CENTER SHIFTING EASTWARD TO NEAR BERMUDA. THIS IS EXPECTED TO ALLOW IRENE TO MOVE SLOWLY NORTHWESTWARD AROUND THE SOUTHWEST PERIPHERY OF THE HIGH. THE OFFICIAL FORECAST IS TO THE LEFT OF THE PREVIOUS ADVISORY AND IS ON THE EXTREME LEFT...OR SOUTH ...SIDE OF THE NHC MODEL GUIDANCE ENVELOPE. IF A WESTWARD MOTION CONTINUES TODAY AND THE CENTER DOES NOT REFORM FARTHER NORTH...THEN THE TRACK WILL HAVE TO BE SHIFTED EVEN MORE TO THE LEFT ON THE NEXT ADVISORY. UPPER-LEVEL OUTFLOW HAS BECOME BETTER ESTABLISHED OVER THE PAST 12 HOURS AND IT IS EXPECTED TO CONTINUE TO IMPROVE FOR THE NEXT 3 DAYS OR SO. HOWEVER...THE AFOREMENTIONED MID-LEVEL NORTHERLY FLOW UNDERCUTTING THE OUTFLOW LAYER IS PRODUCING SOME MID-LEVEL SHEAR... AS WELL AS ADVECTING VERY DRY AIR INTO THE SYSTEM. THE WARM SEA-SURFACE TEMPERATURES AND IMPROVING OUTFLOW PATTERN SHOULD ALLOW FOR AT LEAST SLOW INTENSIFICATION AS INTERMITTENT BURSTS OF DEEP CONVECTION OCCUR NEAR THE CENTER. IT IS POSSIBLE THAT IRENE COULD REACH HURRICANE STRENGTH BEFORE THE END OF THE FORECAST PERIOD. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 10/1500Z 22.4N 57.7W 30 KT 12HR VT 11/0000Z 22.8N 59.4W 35 KT 24HR VT 11/1200Z 23.7N 61.9W 40 KT 36HR VT 12/0000Z 24.6N 64.3W 45 KT 48HR VT 12/1200Z 25.7N 66.6W 50 KT 72HR VT 13/1200Z 27.2N 69.3W 55 KT 96HR VT 14/1200Z 28.5N 71.5W 60 KT 120HR VT 15/1200Z 31.5N 74.5W 60 KT |
