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| #906020 (Received by flhurricane at: 10:58 PM 06.Oct.2017) TCDAT1 Tropical Storm Nate Discussion Number 11 NWS National Hurricane Center Miami FL AL162017 1000 PM CDT Fri Oct 06 2017 Recent data from NOAA and Air Force Reserve reconnaissance flights indicate that Nate continues to strengthen and is near hurricane strength. The NOAA plane measured a maximum 700-mb flight-level wind of 75 kt, but the SFMR instruments on both planes have only measured surface winds as high as 55 kt. It seems that the highest winds haven`t quite mixed down to the surface, but it`s likely that the system is at least producing surface winds of 60 kt, which will be the initial intensity for this advisory. The NOAA flight also reported that an eyewall is forming to the east of Nate`s center. Nate has been accelerating toward the north-northwest between a large cyclonic gyre centered over southern Mexico and a mid-level high located over the southwestern Atlantic, and the initial motion estimate is 340/19 kt. This north-northwestward motion is expected to continue for the next 24 hours, with Nate turning northward and slowing down only slightly around the time it is forecast to cross the northern Gulf coast between 24-36 hours. After landfall, the cyclone is expected to get swept up ahead of a large mid-latitude trough, and accelerate northeastward over the eastern United States. At least up until landfall, the track guidance is in good agreement, and the NHC forecast is relatively unchanged from the previous one. After landfall, the new forecast is just a tad slower in order to give some credence to the slower solution provided by the ECMWF model. Atmospheric and oceanic conditions appear conducive for Nate to continue strengthening up until the time it makes landfall along the northern Gulf coast. Nate is likely to become a hurricane overnight, and the new NHC forecast has been raised to a peak intensity of 75 kt at 24 hours based on guidance from the SHIPS and LGEM models. The intensity consensus and HCCA are lower than that due to the HWRF solution, which shows absolutely no strengthening before landfall. Disregarding that solution, it seems prudent to be above the consensus, close to the upper end of the guidance envelope. Rapid intensification still cannot be ruled out since the indices are showing a 50/50 chance of a 25-kt increase over the next 24 hours. If Nate becomes a hurricane soon, then additional increases in the official intensity forecast may be necessary in subsequent advisories. Aircraft data indicate that Nate is an asymmetric storm, with most of the winds located on the eastern side of the circulation, and this structure is likely to continue until landfall due to the cyclone`s fast forward speed. Therefore, locations to the east of where Nate makes landfall are expected to receive significantly stronger winds than locations to the west of the center. Regardless, there is still too much uncertainty to know exactly where landfall will occur, and all locations within the hurricane warning area should be preparing for hurricane-force winds. KEY MESSAGES: 1. Life-threatening storm surge flooding is likely along portions of the northern Gulf Coast, and a storm surge warning is now in effect from Morgan City, Louisiana, to the Okaloosa/Walton county line in Florida. Residents in these areas should heed any evacuation instructions given by local officials. 2. A hurricane warning is in effect for portions of the northern Gulf Coast from Louisiana to Alabama, and preparations to protect life and property should be rushed to completion in these areas. 3. 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 the potential for flash flooding in these areas. 4. Moisture from Nate interacting with a frontal zone will also bring 2 to 4 inches with isolated totals of 6 inches across the lower Ohio Valley into the central Appalachians Sunday into Monday, which will also increase the risk for flash flooding across these locations. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 22.3N 86.4W 60 KT 70 MPH 12H 07/1200Z 25.1N 87.8W 70 KT 80 MPH 24H 08/0000Z 28.5N 88.9W 75 KT 85 MPH 36H 08/1200Z 31.4N 88.1W 65 KT 75 MPH...INLAND 48H 09/0000Z 34.7N 85.8W 35 KT 40 MPH...INLAND 72H 10/0000Z 40.5N 76.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 11/0000Z 44.5N 63.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 12/0000Z...ABSORBED $$ Forecaster Berg |
