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Hurricane Irma Forecast Discussion Number 46
2017-09-10 16:50:11| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Sun Sep 10 2017 000 WTNT41 KNHC 101450 TCDAT1 Hurricane Irma Discussion Number 46 NWS National Hurricane Center Miami FL AL112017 1100 AM EDT Sun Sep 10 2017 Latest observations from the Air Force Hurricane Hunters had flight-level winds that corresponded to surface winds near 110 kt. Thus, given sampling considerations, the 115-kt intensity is retained for this advisory. Irma should maintain this intensity until the center reaches the southwest Florida coast, and then begin to weaken while the system interacts with the landmass of the Florida peninsula. Increasing southwesterly shear associated with an upper-level trough should also cause weakening of the hurricane during the next day or so. More rapid weakening is likely after Irma moves into the southeastern United States in 24-36 hours, and the cyclone should weaken to a remnant low in 72 hours or sooner. The official intensity forecast is close to the simple and corrected consensus models. The center of Irma wobbled more northward over the past few hours and the initial motion estimate is about 350/8 kt. Irma is embedded within a broad mid-level gyre over the Gulf of Mexico. The cyclone is expected to be steered north-northwestward at a faster forward speed over the next day or two on the eastern side of the gyre. This will take Irma inland over northern Florida early on Monday and the southeastern United States over the next couple of days. The track guidance remains fairly tightly clustered with the ECMWF track a little to the left and slower than the other models. The official track forecast lies between the model consensus and the ECMWF solution. This is just slightly east of the previous official forecast. KEY MESSAGES: 1. Life-threatening wind and storm surge from Irma will continue in the Florida Keys and southwestern Florida today and spread into central and northwestern Florida tonight and Monday. Preparations in central and northwestern Florida should be rushed to completion. 2. There is imminent danger of life-threatening storm surge flooding along much of the Florida west coast, including the Florida Keys, where a Storm Surge Warning is in effect. The threat of catastrophic storm surge flooding is highest along the southwest coast of Florida, where 10 to 15 feet of inundation above ground level is expected. This is a life-threatening situation. 3. Irma will bring life-threatening wind impacts to much of Florida regardless of the exact track of the center. Wind hazards from Irma are also expected to spread northward through Georgia and into portions of Alabama, Tennessee, South Carolina, and North Carolina. 4. Irma is expected to produce very heavy rain and inland flooding across much of Florida and many other parts of the southeast United States. Rainfall occurring very quickly, at 2 to 4 inches per hour, will lead to flash flooding and rapid rises on creeks, streams, and rivers. Significant river flooding is likely over the next five days in the Florida peninsula and southeast Georgia, where average rainfall of 8 to 15 inches and isolated 20 inch amounts are expected. Significant river flooding is also possible beginning Monday and Tuesday in much of eastern and central Georgia, western South Carolina, and western North Carolina, where average rainfall of 3 to 8 inches and isolated 12 inch amounts are expected. Mountainous parts of these states will be especially vulnerable to flash flooding. Farther west, Irma is expected to produce average amounts of 2 to 5 inches in parts of Alabama and Tennessee, where isolated higher amounts and local flooding may occur. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 25.0N 81.5W 115 KT 130 MPH 12H 11/0000Z 26.6N 82.1W 110 KT 125 MPH 24H 11/1200Z 29.2N 83.0W 80 KT 90 MPH 36H 12/0000Z 31.9N 84.6W 40 KT 45 MPH...INLAND 48H 12/1200Z 33.8N 86.7W 30 KT 35 MPH...INLAND 72H 13/1200Z 36.0N 89.0W 25 KT 30 MPH...POST-TROP/INLAND 96H 14/1200Z 38.5N 86.5W 20 KT 25 MPH...POST-TROP/INLAND 120H 15/1200Z...DISSIPATED $$ Forecaster Pasch
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