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Tropical Depression Fourteen Forecast Discussion Number 5
2020-08-21 16:56:53| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Fri Aug 21 2020 000 WTNT44 KNHC 211456 TCDAT4 Tropical Depression Fourteen Discussion Number 5 NWS National Hurricane Center Miami FL AL142020 1100 AM EDT Fri Aug 21 2020 An Air Force Reserve Hurricane Hunter aircraft flew into the depression a few hours ago, and the plane made two center fixes that were about 35 n mi apart, indicating that there are likely multiple low-level swirls rotating around a common center. A well-defined swirl coincident with the second center fix has become apparent in visible satellite imagery, but for now a blend of the aircraft fixes is being used for the initial position until we can be sure the satellite feature is in fact the one and only center. Flight-level and SFMR winds, outside of heavy rainfall, indicate that the maximum winds remain 30 kt. Deep convection is still lacking in organization, with the heaviest activity well to the north near the Cayman Islands and along the Honduras coast. The depression is moving northwestward, or 305/12 kt, along the southwestern periphery of an Atlantic subtropical ridge and toward a deep-layer trough over the Gulf of Mexico. This northwestward motion is expected to persist for the entire 5-day forecast period, with a decrease in forward speed anticipated while the cyclone approaches the Yucatan coast. The track guidance has slowed down a bit during that time, especially the GFS, and the new NHC forecast is therefore a little slower than the previous forecast. After that time, an increase in forward speed is expected, and the NHC forecast lies to the west of the TVCN model consensus, closer to the GFS, ECMWF, and HCCA scenarios. The structure of the depression aside, the environment still appears conducive for strengthening while the system approaches the Yucatan Peninsula. Vertical shear over the depression is currently less than 10 kt and is expected to remain low for the next 36-48 hours, and sea surface temperatures will be around 30 degrees Celsius. Therefore, steady intensification is shown in the official forecast through 36 hours, and the NHC prediction lies near the upper end of the guidance envelope between the HCCA and HWRF solutions just before the center reaches the Yucatan coast. After some weakening while over the Yucatan Peninsula, re-intensification is likely to occur over the central Gulf of Mexico between days 2 and 3 while vertical shear remains relatively low, and the cyclone could become a hurricane during that time, as shown by the HCCA, HWRF, and HMON models. After day 3, southwesterly vertical shear of 30 kt or more is expected to develop over the northwestern Gulf, and the official forecast follows the trend of all the intensity guidance, showing weakening by day 4 as the cyclone approaches the southeastern Texas or southwestern Louisiana coastline. This forecast remains highly uncertain, however, and users are urged to continue monitoring changes to this forecast over the next couple of days. Key Messages: 1. Heavy rainfall and gusty winds over portions of the coasts of Nicaragua and Honduras, including the Bay Islands, are expected to diminish today. 2. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and it is expected to be near or at hurricane strength when it reaches the east coast of the Yucatan Peninsula of Mexico late Saturday. A Hurricane Watch and a Tropical Storm Warning are in effect for portions of that region. 3. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Some strengthening is anticipated while it moves northwestward over the central Gulf of Mexico early next week, but it is too soon to know exactly how strong it will get or the location and magnitude of impacts it will produce along the central or northwestern Gulf Coast. Interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 16.6N 84.1W 30 KT 35 MPH 12H 22/0000Z 17.4N 85.0W 40 KT 45 MPH 24H 22/1200Z 18.6N 85.9W 50 KT 60 MPH 36H 23/0000Z 20.0N 86.9W 60 KT 70 MPH 48H 23/1200Z 21.5N 88.2W 50 KT 60 MPH...INLAND 60H 24/0000Z 23.2N 89.7W 55 KT 65 MPH...OVER WATER 72H 24/1200Z 25.1N 91.4W 65 KT 75 MPH 96H 25/1200Z 28.7N 94.1W 60 KT 70 MPH 120H 26/1200Z 31.3N 95.5W 40 KT 45 MPH...INLAND $$ Forecaster Berg
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