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#39221 (Received by flhurricane at: 10:46 PM 12.Aug.2005) TCDAT4 TROPICAL STORM IRENE DISCUSSION NUMBER 34 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT FRI AUG 12 2005 SINCE THE LAST RECON REPORT AND 00Z SATELLITE INTENSITY ESTIMATES ...IRENE'S CONVECTIVE PATTERN HAS DEGRADED SOMEWHAT. A 12/2245Z SSMI OVERPASS INDICATED A SHARP DRY SLOT HAD PUSHED INTO THE CIRCULATION FROM THE NORTH...ALL THE WHILE CLOUD TOPS HAVE WARMED NEAR THE CENTER AND A CDO FEATURE IS NO LONGER EVIDENT IN INFRARED IMAGERY. THEREFORE...THE INTENSITY IS BEING MAINTAINED AT 60 KT. HOWEVER... THE CENTRAL PRESSURE HAS BEEN DECREASED TO 991 MB BASED ON A 12/2300Z PRESSURE OF 995.9 MB REPORTED BY BUOY 41927 LOCATED ABOUT 30 NMI NORTHEAST OF THE CENTER...WHICH WAS LOWER THAN THE LAST RECON REPORTED CENTRAL PRESSURE OF 997 MB AT 12/2023Z. THE BEST MOTION ESTIMATE REMAINS 310/09...WHICH IS A LITTLE TO THE RIGHT OF THE RECON FIX MOTION. A NOAA G-IV JET AIRCRAFT AND AN AIR FORCE RESERVE AIRCRAFT HAVE BEEN CONDUCTING SYNOPTIC SURVEILLANCE MISSIONS AROUND IRENE THIS EVENING. DROPSONDE DATA FROM THOSE AIRCRAFT INDICATE A SLIGHTLY STRONGER AND MORE WESTWARD EXTENSION OF THE MID-LEVEL RIDGE THAN ANY OF THE MODELS WERE INDICATING FOR 13/00Z...WITH THE UKMET HAVING THE CLOSEST VERIFICATION. THE RIDGE ...ALBEIT SOMEWHAT NARROW...EXTENDS FROM NEAR BERMUDA WESTWARD TO NORTH CAROLINA. A SHORTWAVE TROUGH HAS MOVED EASTWARD OFF THE U.S. EAST COAST AND A SHORTWAVE RIDGE OVER THE EASTERN OHIO VALLEY IS MOVING EASTWARD TO TAKE THE PLACE OF THAT TROUGH. IN THE SHORT TERM ...THIS SHOULD BUILD OR AT LEAST MAINTAIN THE EXISTING RIDGE TO THE NORTH OF IRENE...WHICH MAY CAUSE A LITTLE MORE WESTWARD MOTION THAN FORECAST FOR THE NEXT 24 HOURS OR SO. AFTER THAT...ALL THE MODELS AGREE THAT IRENE WILL ERODE THE RIDGE AND MOVE SLOWLY NORTHWARD THROUGH THE RIDGE BETWEEN 70-72W LONGITUDE...AND THEN TURN EAST-NORTHEASTWARD BY 72 HOURS. HOWEVER...GIVEN MORE RIDGE SHOWING UP IN THE SYNOPTIC DROPSONDE DATA...THERE MAY BE A WESTWARD SHIFT IN THE 00Z MODEL GUIDANCE. FOR THIS ADVISORY...THOUGH...THE OFFICIAL TRACK WILL REMAIN CLOSE TO THE PREVIOUS FORECAST TRACK. BRIEF PERIODS OF INTENSIFICATION WILL PROBABLY OCCUR THROUGH AT LEAST THE NEXT 48 HOURS OR SO...DESPITE WARM SSTS OF AT LEAST 28C AND FAVORABLE UPPER-LEVEL SHEAR CONDITIONS. THIS IS MAINLY DUE TO THE VERY DRY AIR THAT IRENE WILL BE MOVING THROUGH AND CONSTANTLY HAVING TO MIX OUT. THE OFFICIAL INTENSITY FORECAST IS CLOSE TO THE PREVIOUS ADVISORY AND REMAINS A LITTLE STRONGER THAN THE SHIPS INTENSITY MODEL...BUT MUCH HIGHER THAN THE GFDL MODEL...WHICH WEAKENS IRENE TO LESS THAN 30 KT IN 48H. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 13/0300Z 29.2N 68.3W 60 KT 12HR VT 13/1200Z 29.9N 69.3W 65 KT 24HR VT 14/0000Z 31.4N 70.3W 70 KT 36HR VT 14/1200Z 33.0N 70.6W 75 KT 48HR VT 15/0000Z 34.6N 70.5W 75 KT 72HR VT 16/0000Z 36.7N 70.0W 75 KT 96HR VT 17/0000Z 38.0N 67.5W 75 KT 120HR VT 18/0000Z 39.0N 61.5W 75 KT |