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#38414 (Received by flhurricane at: 5:05 PM 08.Aug.2005) TCDAT4 TROPICAL DEPRESSION IRENE DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT MON AUG 08 2005 CONVECTION HAS PERSISTED TO THE EAST OF THE LOW LEVEL CENTER THIS AFTERNOON... OFTEN EMANATING FROM THE CENTER ITSELF. HOWEVER... THE LOW LEVEL CENTER REMAINS EXPOSED DVORAK INTENSITY ESTIMATES REMAIN T2.0/30 KT. ALTHOUGH IT IS POSSIBLE THAT TROPICAL STORM FORCE WINDS ARE REACHING THE SURFACE IN A LIMITED AREA WITHIN THE SPARSE CONVECTION... IRENE IS MAINTAINED AS 30 KT DEPRESSION FOR THIS ADVISORY. THE SYSTEM IS STRUGGLING TO REORGANIZE WITHIN A FAIRLY DRY AND STABLE ENVIRONMENT WITH MODERATE VERTICAL SHEAR. THESE CONDITIONS SHOULD BE SLOW TO CHANGE ALONG THE FORECAST TRACK... AND ACCORDINGLY THE SHIPS GUIDANCE SHOWS GRADUAL STRENGTHENING TO 45 KT BY 60 HOURS...CONTINUING ON TO 62 KT BY 120 HOURS. HOWEVER... THE GFDL DISSIPATES THE SYSTEM WITHIN A COUPLE OF DAYS. THE OFFICIAL FORECAST WILL COMPROMISE AND REMAIN SIMILAR TO THE PREVIOUS ADVISORY... SHOWING MODEST AND GRADUAL STRENGTHENING. WHEN THE CONVECTION REDEVELOPED THIS MORNING... THE LOW LEVEL CENTER SLOWED DOWN IN RESPONSE. SMOOTHING THROUGH THE STOP-AND-GO MOTION DURING THE PAST 12 HOURS OR SO YIELDS AN INITIAL MOTION OF 285/10. THE NEW OFFICIAL FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS ADVISORY... AND THERE IS A LITTLE MORE CONFIDENCE IN THIS TRACK NOW SINCE SOME OF THE MODELS THAT WERE EASTERN OUTLIERS THIS MORNING... SUCH AS THE UKMET AND NOGAPS... HAVE SHIFTED WESTWARD. THEREFORE... MODELS ARE COMING INTO BETTER AGREEMENT THAT A SYSTEM OF MODERATE TROPICAL STORM STRENGTH WILL MOVE WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE LOWER/MID LEVEL SUBTROPICAL RIDGE. THE SLOW MOTION SHOWN AT THE END OF THE OFFICIAL FORECAST IS INDICATIVE OF THE GREAT UNCERTAINTY LATE IN THE PERIOD...WHEN THE SPREAD IN THE MODELS IS STILL QUITE SIGNIFICANT. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 08/2100Z 22.5N 51.5W 30 KT 12HR VT 09/0600Z 23.0N 53.1W 30 KT 24HR VT 09/1800Z 23.6N 55.4W 35 KT 36HR VT 10/0600Z 24.3N 57.8W 35 KT 48HR VT 10/1800Z 25.1N 59.7W 40 KT 72HR VT 11/1800Z 27.0N 63.5W 40 KT 96HR VT 12/1800Z 29.5N 66.5W 45 KT 120HR VT 13/1800Z 31.5N 67.0W 45 KT |