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| #877312 (Received by flhurricane at: 11:01 PM 07.Oct.2016) TCDAT4 HURRICANE MATTHEW DISCUSSION NUMBER 40 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 1100 PM EDT FRI OCT 07 2016 Coastal Doppler radar data this evening indicate that Matthew is gradually becoming less organized. The eyewall has broken open with the remaining deep convection in a band just north of the center, and there is now little precipitation in the southeastern quadrant. A combination of radar winds and earlier aircraft data suggests that the intensity has decreased slightly since the last advisory, so the initial intensity is lowered to 90 kt. The initial motion is now 010/10 kt. During the next 36 hours, Matthew should turn more northeastward as it moves along the southern edge of a mid-latitude trough. The forecast track, which lies in the center of the track guidance envelope, has the center moving near the coasts of Georgia and South Carolina during the next 12-18 hours, then near the North Carolina coast from 18-36 hours. While this occurs, the cyclone is forecast to encounter strong vertical wind shear and to entrain dry air associated with an approaching frontal system. This should result in a steady weakening, and Matthew is now forecast to weaken to a tropical storm by 36 hours in agreement with the SHIPS model. It is possible that Matthew could merge with the frontal system at about 36 hours, although none of the available guidance currently forecasts the system to become an extratropical low. The track and intensity forecasts become very low confidence after 36 hours due to a large diversity of model solutions. The GFDL and HWRF forecast Matthew to turn northeastward and become an extratropical low near the Canadian Atlantic provinces. The UKMET moves Matthew eastward and eventually has it absorbed by Tropical Storm Nicole. The ECMWF, NAVGEM, and Canadian models show a southwestward turn, with the cyclone or it remnants near the Bahamas by 120 hours. The GFS is between the UKMET and ECMWF, showing Matthew moving far enough to the east to interact with Nicole, then turning southward. The new track forecast follows the previous advisory in showing a southward/southwestward turn similar to the ECMWF, but is east of the previous track due to an overall eastward trend in the guidance. Regarding the intensity, the GFS suggests that Matthew could decay to a remnant low by 120 hours, while the ECMWF suggests the system could still be a tropical cyclone. Either way, continued weakening is likely due to shear and dry air entrainment, and the official forecast calls for Matthew to weaken to a depression by 96 hours. Due to the degradation of the radar signature of Matthew, the hourly Tropical Cyclone Updates will no longer be issued. KEY MESSAGES: 1. We have been very fortunate that Matthew's strongest winds have remained a short distance offshore of the Florida and Georgia coasts thus far, but this should not be a reason to let down our guard. Only a small deviation to the left of the forecast track could bring these winds onshore. The western eyewall of Matthew, which contains hurricane-force winds, is expected to move over or very near the coasts of Georgia and South Carolina tonight and Friday. 2. Hurricane winds increase very rapidly with height, and occupants of high-rise buildings along the coast are at particular risk of strong winds. Winds at the top of a 30-story building will average one Saffir-Simpson category higher than the winds near the surface. 3. The water hazards remain, even if the core of Matthew remains offshore. These include the danger of life-threatening inundation from storm surge, as well as inland flooding from heavy rains from Florida to North Carolina. 4. The National Hurricane Center is issuing Potential Storm Surge Flooding Maps, and Prototype Storm Surge Watch/Warning Graphics for Matthew. It is important to remember that the Potential Storm Surge Flooding Map does not represent a forecast of expected inundation, but rather depicts a reasonable worst-case scenario -- the amount of inundation that has a 10 percent chance of being exceeded. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 31.2N 80.5W 90 KT 105 MPH 12H 08/1200Z 32.5N 79.8W 80 KT 90 MPH 24H 09/0000Z 33.6N 77.8W 70 KT 80 MPH 36H 09/1200Z 33.9N 75.5W 60 KT 70 MPH 48H 10/0000Z 33.0N 74.0W 55 KT 65 MPH 72H 11/0000Z 30.0N 73.5W 40 KT 45 MPH 96H 12/0000Z 27.5N 74.5W 30 KT 35 MPH 120H 13/0000Z 26.0N 75.5W 30 KT 35 MPH $$ Forecaster Beven |
