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| #943576 (Received by flhurricane at: 10:59 PM 08.Oct.2018) TCDAT4 Hurricane Michael Discussion Number 10 NWS National Hurricane Center Miami FL AL142018 1000 PM CDT Mon Oct 08 2018 Data from NOAA and Air Force Reserve hurricane hunter aircraft this evening indicate that Michael has continued to strengthen...despite westerly vertical shear of about 20 kt, which is most unusual. The maximum 8000-ft flight-level winds measured by NOAA so far has been 102 kt and maximum SFMR surface wind speed was 78 kt. The central pressure measured by the two aircraft has been fluctuating between 970 mb and 974 mb, which is likely due to small mesovortices rotating around inside the fairly large 35-nmi-wide eye. Given the aforementioned wind data and the possibility of locally enhanced winds due to the mesovortices, the initial intensity has only been increased to 80 kt rather than 85 kt, which the NOAA flight-level wind data would typically support. The initial motion estimate is 350/11 kt. The steering flow pattern isn't forecast to change much, if at all, for the next 36-48 hours, with Michael expected to remain caught between a deep-layer ridge centered off of the U.S. east coast and a highly amplitude mid-latitude trough over the U.S. Plains states and northern Mexico. The combined deep-layer southerly flow should keep the hurricane moving northward to north-northwestward for the next 36 hours or so. Shortly thereafter and just prior to landfall, the approaching mid-latitude trough is expected to turn Michael toward the north-northeast or northeast. By 48 hours and beyond, significant acceleration toward the northeast ahead of the trough is forecast to continue through the 120-h period, with Michael emerging off of the U.S. mid-Atlantic coast around 96 hours. The new NHC forecast track was nudged slightly to the east of the previous track through 36 h, based on the more eastward initial position and a forward motion that is still to the right or east of short term motion in the model guidance, but is still near the consensus models TVCN, TVCX, and NOAA-HCCA. By 48 hours and beyond, the official track is close to the previous advisory track. Michael's steady intensification over the past 48 hours in the face of 20-kt westerly shear defies traditional logic. Either the shear calculations are unrepresentative or Michael has become more inertially stable due to its large eye and large outer wind field, making it more shear resistant. Having said that, all of the model guidance calls for the shear to decrease to around 10 kt or less by 36 hours, which argues for at least steady intensification during that time given that Michael will be moving over warm SSTs of 28.5C-29C, which are about 1-2 deg C above average for this time of the year. Less-than-normal weakening after landfall in the 48- to 96-h period is expected due to Michael's fast forward speed of 20-30 kt. Re-strengthening as an extratropical low over water on days 4 and 5 is forecast due to baroclinic interaction with a frontal system and the cyclone being back over warm Atlantic waters. The official intensity forecast is a little higher than the consensus models IVCN and HCCA, and is similar to the previous advisory and the FSSE model. It should be noted that the location and magnitude of peak storm surge flooding is very sensitive to small changes in the track, intensity, and structure of the hurricane. Since there is still uncertainty in all of these parameters, the official NHC storm surge forecast and watch/warning areas includes various plausible scenarios. Regardless of the eventual track and intensity of Michael, life-threatening storm surge inundation is expected along portions of the Florida Panhandle and Big Bend/Nature Coast, and the storm surge watch has been upgraded to a storm surge warning for parts of this area. The NOAA G-IV aircraft is currently conducting a synoptic surveillance mission over the Gulf of Mexico and dropsondes from that mission will be assimilated into the 0000 UTC numerical models runs. Key Messages: 1. Life-threatening storm surge is likely along portions of the coasts of the Florida Panhandle, Big Bend, and Nature Coast, and a storm surge warning is in effect for these areas. Residents in these areas should follow all advice given by their local officials. 2. A hurricane warning has been issued for portions of the Florida Gulf Coast, and everyone in these areas should prepare for life-threatening winds associated with the core of Michael. Damaging winds will also extend inland across portions of the Florida Panhandle, southern Georgia, and southeast Alabama as Michael moves inland. 3. Heavy rainfall from Michael could produce life-threatening flash flooding from the Florida Panhandle and Big Bend region into portions of Georgia and South Carolina. 4. Hurricane conditions will continue in portions of western Cuba through this evening, where a hurricane warning is in effect. 5. Michael is expected to produce heavy rainfall and flash flooding over portions of western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 23.2N 85.3W 80 KT 90 MPH 12H 09/1200Z 24.7N 85.9W 90 KT 105 MPH 24H 10/0000Z 26.8N 86.3W 100 KT 115 MPH 36H 10/1200Z 29.1N 85.9W 105 KT 120 MPH 48H 11/0000Z 31.4N 84.4W 55 KT 65 MPH...INLAND 72H 12/0000Z 35.9N 77.3W 45 KT 50 MPH...INLAND 96H 13/0000Z 41.5N 63.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 14/0000Z 47.8N 46.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart |
