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Tropical Storm Michael Forecast Discussion Number 5
2018-10-07 23:01:14| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Sun Oct 07 2018 000 WTNT44 KNHC 072101 TCDAT4 Tropical Storm Michael Discussion Number 5 NWS National Hurricane Center Miami FL AL142018 400 PM CDT Sun Oct 07 2018 Deep convection has continued to develop over the eastern semicircle of the cyclone, and data from the reconnaissance aircraft indicate that the center has re-formed farther east, closer to the convection. The Air Force aircraft has measured peak 925-mb flight-level winds of 56 kt, and believable SFMR winds of 40-45 kt. Based on these data, the initial wind speed has been increased to 45 kt. Due to the center reformation, the initial motion estimate is a highly uncertain 020/3 kt. The overall forecast reasoning has not changed much since the previous advisory. Although there could be some additional eastward re-formation of the center, the tropical storm is forecast to begin moving northward between a ridge over the western Atlantic and a deep-layer trough over the west-central United States. A general northward motion at around 10 kt is then expected to continue during the next 2 to 3 days. After that time, Michael should turn northeastward ahead of an approaching trough. The track guidance remains in overall agreement on this scenario, however, significant along-track (forward speed and timing) differences remain. The HWRF brings Michael onshore the northern Gulf coast within 72 hours, while the ECMWF is much slower and has Michael still offshore at day 4. The new NHC track has been shifted eastward primarily in the short term due to the more eastward initial position. The latter portion of the track forecast is again close to the consensus aids due to the large along- and cross-track guidance spread. Michael has strengthened today despite moderate westerly shear. The shear is forecast to gradually decrease over the next couple of days while the system moves over warm waters. This should allow for steady strengthening and most of the intensity models bring Michael to hurricane strength within the next couple of days. It should also be noted that the global models also significantly deepen the storm over the next 72 hours to pressures below 970 mb. The new NHC intensity forecast calls for Michael to become a hurricane in about 36 hours when the storm reaches the southeastern Gulf of Mexico. Additional strengthening is indicated through 72 hours when the storm is forecast to be near the northern Gulf coast, and the NHC forecast is near the higher SHIPS and HWRF models. Key Messages: 1. 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. 2. Tropical storm conditions are expected tonight over portions of western Cuba and the northeastern Yucatan Peninsula, where tropical storm warnings are in effect. 3. Michael is forecast to be a hurricane when it reaches the northeastern Gulf Coast by mid-week, and the risk of dangerous storm surge, rainfall, and wind impacts continues to increase. In addition, Michael is expected to affect portions of the Florida Gulf Coast that are especially vulnerable to storm surge, regardless of the storm's exact track or intensity. Residents in these areas should monitor the progress of this system and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 19.2N 85.5W 45 KT 50 MPH 12H 08/0600Z 20.1N 85.6W 50 KT 60 MPH 24H 08/1800Z 21.5N 85.8W 60 KT 70 MPH 36H 09/0600Z 23.2N 86.2W 70 KT 80 MPH 48H 09/1800Z 25.0N 86.7W 80 KT 90 MPH 72H 10/1800Z 29.2N 85.7W 85 KT 100 MPH 96H 11/1800Z 33.7N 80.4W 50 KT 60 MPH...INLAND 120H 12/1800Z 39.0N 68.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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