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| #905802 (Received by flhurricane at: 10:49 AM 05.Oct.2017) TCDAT1 Tropical Storm Nate Discussion Number 5 NWS National Hurricane Center Miami FL AL162017 1100 AM EDT Thu Oct 05 2017 The cloud pattern associated with Tropical Depression Sixteen increased in organization after the last advisory, with the formation of a ragged central convective feature and outer banding in the northeastern semicircle. In addition, data from the Colombian radar at San Andres showed a partial eyewall, and surface observations from Puerto Cabezas, Nicaragua, included a pressure of 1001 mb outside of the center. Based on these data, the initial intensity has been increased to 35 kt, and the depression has been upgraded to Tropical Storm Nate. The center of Nate is now inland over northeastern Nicaragua, and little change in strength is expected until the center moves over the northwestern Caribbean Sea. After that, a combination of warm sea surface temperatures and light shear should allow for at least steady strengthening. However, the guidance is producing mixed signals despite a favorable-looking environment. The Rapid Intensification Index of the SHIPS model is showing high chances of rapid intensification, with better than a 50 percent chance of 25 kt of strengthening in the next 24 h and nearly a 50 percent chance of 65 kt of strengthening in 72 h. On the other side, the GFS and Canadian models show only modest development and keep the cyclone as a tropical storm until it reaches the northern Gulf coast. Given the environment, the intensity forecast leans towards the high end of the guidance envelope and calls for Nate to become a hurricane in about 48 h and reach the northern Gulf Coast as a hurricane. The initial motion is 325/8. A combination of a large cyclonic gyre over Central America, a trough of low pressure moving westward across the Gulf of Mexico, and a building subtropical ridge over the western Atlantic should steer Nate generally north-northwestward with an increase in forward speed during the next 72 h. While the guidance is in better agreement on the direction that Nate should move, there remains disagreement on the speed despite an overall trend toward a faster motion. The new forecast track is similar to the direction of the previous track, but shows a faster forward speed that has the center near the northeastern Yucatan Peninsula in about 36 h and near the northern Gulf Coast in about 72 h. After the Gulf Coast landfall, Nate or its remnants are expected to recurve northeastward upon encountering the mid-latitude westerlies. KEY MESSAGES: 1. Heavy rainfall is the main threat from Nate in portions of Central America, with life-threatening flash flooding and mud slides possible in portions of Nicaragua, Honduras, Costa Rica, Panama, and Belize through Friday night. 2. Nate is forecast to be near hurricane intensity when it approaches the Yucatan Peninsula late Friday, bringing direct impacts from wind, storm surge, and heavy rainfall. A tropical storm warning and a hurricane watch are in effect for a portion of this area and life-threatening flash flooding is also possible. 3. Nate is forecast to reach the northern Gulf Coast this weekend as a hurricane, and the threat of direct impacts from wind, storm surge, and heavy rainfall is increasing. However, it is too early to specify the exact timing, location, or magnitude of these impacts. Residents along the Gulf Coast from Louisiana through the Florida Panhandle should monitor the progress of Nate and heed any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 14.3N 83.7W 35 KT 40 MPH...INLAND 12H 06/0000Z 15.6N 84.3W 35 KT 40 MPH...INLAND 24H 06/1200Z 18.1N 85.4W 45 KT 50 MPH...OVER WATER 36H 07/0000Z 20.8N 86.8W 55 KT 65 MPH 48H 07/1200Z 23.7N 88.1W 65 KT 75 MPH 72H 08/1200Z 29.5N 89.5W 70 KT 80 MPH 96H 09/1200Z 36.0N 85.0W 30 KT 35 MPH...INLAND 120H 10/1200Z 41.5N 76.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Beven |
