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Tropical Depression Fourteen Forecast Discussion Number 3
2020-08-21 04:58:15| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Thu Aug 20 2020 000 WTNT44 KNHC 210258 TCDAT4 Tropical Depression Fourteen Discussion Number 3 NWS National Hurricane Center Miami FL AL142020 1100 PM EDT Thu Aug 20 2020 The overall convective pattern has improved somewhat since the previous advisory, with a band of deep convection having developed near and just south of the low-level center. A pronounced mid-level circulation has been rotating westward to the north of the center of the broader low-level circulation, which has likely prevented the cyclone from becoming a tropical storm by now, especially given the very impressive outflow pattern. However, NOAA buoy 42057 to the north of the center recently reported a sustained wind of 29 kt at 4 meters elevation, which equals about a 32-kt 10-meter wind speed, which means that the cyclone isn't far from becoming a tropical storm. The intensity is being maintained at 30 kt until convection becomes more persistent. The center has been reforming a little farther north and has also slowed down, with the initial motion now being west-northwestward or 285/12 kt. The slower and farther north initial position has required a slight northward shift in the forecast track for the next 24 hours and, as a result, the center of the cyclone is no longer expected to make landfall very far inland over Honduras or Nicaragua, if it makes landfall at all. By 36 hours, the new NHC forecast track shifts back closer to the previous advisory track due to a strong mid-level ridge extending westward across Florida and into the eastern and central Gulf of Mexico. That feature is expected to keep the cyclone moving in a general northwestward direction on days 2-5, resulting in landfall over the northeastern Yucatan Peninsula on Saturday, and be approaching the northwestern Gulf coast by the middle of next week. The official forecast track lies along the southern edge of the guidance envelope, close to the middle of the simple consensus models and a little south of the NOAA-HCCA corrected model. Due to the northward shift in the new forecast track, the center and inner-core wind field of the cyclone will not be disrupted as much as previously expected, which has significant implications in the intensity forecast. The depression is now expected to reach hurricane strength just before it makes landfall on the east side of the Yucatan Peninsula in about 48 hours. Weakening is forecast in 60 hours while the cyclone moves across northeastern Yucatan, followed by gradual re-strengthening thereafter. Ocean temperatures along the path of the cyclone are forecast to be 30.0-30.5 deg C and the vertical shear is expected to remain low at less than 10 kt through 96 hours. Those conditions coupled with the impressive outflow pattern should allow for at least typical strengthening. By 120 hours, the GFS- and ECMWF-based SHIPS models show the vertical wind shear increasing sharply from the southwest to 20-25 kt, which would normally induce weakening. However, it appears that those models are incorporating some strong jetstream winds of 60-70 kt well to the northwest of the center of the cyclone, which has resulted in high bias in the shear output. Therefore, the cyclone is forecast to be near hurricane strength when it approaches the Texas coast in 120 hours. The new intensity forecast is similar to but a little higher then the previous advisory due to less land interaction than previously expected, and is is a blend of the Decay-SHIPS and LGEM models, which are at the upper-end of the guidance envelope. Key Messages: 1. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and is likely to produce tropical-storm-force winds and heavy rainfall over portions of the coasts of Nicaragua and Honduras, including the Bay Islands, beginning tonight through Friday. The system is expected be near or at hurricane strength when it reaches the Yucatan Peninsula of Mexico late Saturday where a Hurricane Watch and a Tropical Storm Warning are in effect. 2. 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 western 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 21/0300Z 14.9N 82.2W 30 KT 35 MPH 12H 21/1200Z 15.5N 83.8W 35 KT 40 MPH 24H 22/0000Z 16.8N 85.1W 45 KT 50 MPH 36H 22/1200Z 18.2N 86.0W 55 KT 65 MPH 48H 23/0000Z 19.8N 87.2W 65 KT 75 MPH 60H 23/1200Z 21.4N 88.5W 40 KT 45 MPH...INLAND 72H 24/0000Z 23.2N 89.8W 50 KT 60 MPH...OVER WATER 96H 25/0000Z 26.7N 92.3W 65 KT 75 MPH 120H 26/0000Z 29.1N 94.3W 65 KT 75 MPH $$ Forecaster Stewart
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