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Hurricane Nate Forecast Discussion Number 13
2017-10-07 17:04:35| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sat Oct 07 2017 000 WTNT41 KNHC 071504 CCA TCDAT1 Hurricane Nate Discussion Number 13...Corrected NWS National Hurricane Center Miami FL AL162017 1000 AM CDT Sat Oct 07 2017 Corrected 24 kt motion to 23 kt motion in third paragraph Nate is showing improved organization in satellite imagery this morning, with the formation of a symmetric central dense overcast with cloud tops colder than -80C. In addition, Air Force Reserve and NOAA Hurricane Hunter aircraft have reported a central pressure near 984 mb inside a 25 n mi wide eye that is starting to form under the overcast. The planes have reported 700-mb flight level winds of up to 88 kt and surface wind estimates from the SFMR instrument between 75-85 kt. Based on these data, the initial intensity is increased to a possibly conservative 80 kt. Conditions appear favorable for Nate to continue strengthening for the next 12 h or so before it encounters land and increasing shear. The new intensity forecast thus follows the SHIPS model in showing Nate become a Category 2 hurricane before landfall on the central Gulf Coast. After landfall, Nate should weaken rapidly as it moves through the eastern United States. The cyclone is now forecast to become extratropical near the 72 hr point and dissipate completely by 96 h. The initial motion is toward the north-northwest at a very rapid 23 kt. The hurricane is being steered by the flow between a large cyclonic gyre over the southwestern Gulf of Mexico and a mid-level ridge over the western Atlantic. In addition, a mid-latitude trough in the westerlies is moving eastward through the central United States. This pattern is expected to cause Nate to turn northward during the next 12-18 h as it rounds the western end of the ridge, followed by a turn toward the northeast as it enters the westerlies. The new forecast track is nudged a little to the left of the previous track, and it lies near the center of the tightly clustered guidance. KEY MESSAGES: 1. Nate is expected to bring life-threatening storm surge flooding near and well east of where the center makes landfall, and a storm surge warning is in effect from Morgan City, Louisiana, to the Okaloosa/Walton county line in Florida. Maximum flooding of 7 to 11 feet above ground level is expected in portions of southeastern Louisiana and along the Mississippi coast. Residents in these areas should immediately heed any evacuation instructions given by local officials. 2. Nate is forecast to reach Category 2 intensity before landfall. A hurricane warning is in effect for portions of the northern Gulf Coast from Louisiana to Alabama, with the strongest winds expected to occur primarily to the east of the center. Preparations to protect life and property should be rushed to completion in these areas, as tropical storm conditions will first arrive in the warning area this afternoon. 3. Nate's fast forward speed after landfall will bring tropical- storm-force winds well inland across portions of the southeastern U.S. Tropical storm watches and warnings are in effect for portions of southeastern Mississippi, Alabama, and western Georgia. 4. Nate will bring heavy rainfall of 3 to 6 inches with isolated totals of 10 inches east of the Mississippi River from the central Gulf Coast into the Deep South, eastern Tennessee Valley, and southern Appalachians through Monday, resulting in the potential for flash flooding in these areas. 5. Moisture from Nate interacting with a frontal zone will also bring 2 to 4 inches of rain with isolated totals of 6 inches across the Ohio Valley and central Appalachians Sunday and Monday, which will increase the risk for flash flooding across these locations. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 26.6N 88.4W 80 KT 90 MPH 12H 08/0000Z 29.1N 89.0W 90 KT 105 MPH 24H 08/1200Z 32.1N 88.3W 60 KT 70 MPH...INLAND 36H 09/0000Z 35.7N 85.5W 35 KT 40 MPH...INLAND 48H 09/1200Z 39.2N 80.6W 30 KT 35 MPH...INLAND 72H 10/1200Z 44.5N 67.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 11/1200Z...DISSIPATED $$ Forecaster Beven
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