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ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Hurricane Irma Discussion Number 23 NWS National Hurricane Center Miami FL AL112017 1100 PM AST Mon Sep 04 2017 Irma's satellite presentation remains quite impressive with a well-defined eye and a symmetrical CDO containing very cold cloud tops. Flight-level and SFMR-observed surface winds from NOAA and Air Force Hurricane Hunter aircraft indicate that the current intensity is about 120 kt. Since the hurricane will be moving through an environment of low vertical wind shear, a moist mid-level atmosphere, and increasing upper-ocean heat content, additional intensification is likely. The only expected impediment to strengthening should be eyewall replacement cycles, which are difficult to predict. The official intensity forecast is very close to the latest model consensus, ICON. Although the consensus of the guidance shows slight weakening in the 96- to 120-hour time frame, Irma is forecast to remain a powerful hurricane throughout the 5-day forecast period. Center fixes from the aircraft indicate a westward motion of about 270/11 kt. Irma should turn toward the west-northwest tomorrow while it is steered by the flow to the south of a mid-level ridge. A broad trough is forecast to amplify over the eastern U.S. in 72 hours and then lift northeastward leaving a weakness in the ridge to north of the hurricane. This should cause a slowing of the forward speed near the end of the forecast period. The official track forecast is similar to the previous one and is close to the model consensus. Users are reminded to not focus on the exact forecast track, especially at the longer ranges, since the average NHC track errors are about 175 and 225 statute miles at days 4 and 5, respectively. KEY MESSAGES: 1. Irma is expected to affect the northeastern Leeward Islands a dangerous major hurricane, accompanied by life-threatening wind, storm surge, and rainfall impacts. Hurricane warnings are in effect for portions of the Leeward Islands. Preparations should be rushed to completion, as tropical-storm force winds are expected to first arrive in the hurricane warning area by late Tuesday. 2. Irma is also expected affect the British and U.S. Virgin Islands and Puerto Rico as a dangerous major hurricane later this week. Hurricane warnings have been issued for these areas, and tropical-storm-force winds could arrive in these areas by early Wednesday. 3. Irma could directly affect Hispaniola, the Turks and Caicos, the Bahamas, and Cuba as a dangerous major hurricane later this week. Residents in these areas should monitor the progress of Irma and listen to advice given by officials. 4. There is an increasing chance of seeing some impacts from Irma in the Florida Peninsula and the Florida Keys later this week and this weekend. Otherwise, it is still too early to determine what direct impacts Irma might have on the continental United States. However, everyone in hurricane-prone areas should ensure that they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 16.7N 55.6W 120 KT 140 MPH 12H 05/1200Z 16.9N 57.4W 125 KT 145 MPH 24H 06/0000Z 17.5N 60.0W 130 KT 150 MPH 36H 06/1200Z 18.3N 62.7W 130 KT 150 MPH 48H 07/0000Z 19.3N 65.5W 125 KT 145 MPH 72H 08/0000Z 21.2N 71.0W 120 KT 140 MPH 96H 09/0000Z 22.5N 76.0W 115 KT 130 MPH 120H 10/0000Z 24.0N 80.0W 115 KT 130 MPH $$ Forecaster Pasch NNNN