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Tropical Depression Fourteen Forecast Discussion Number 1
2020-08-20 16:56:38| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Thu Aug 20 2020 046 WTNT44 KNHC 201456 TCDAT4 Tropical Depression Fourteen Discussion Number 1 NWS National Hurricane Center Miami FL AL142020 1100 AM EDT Thu Aug 20 2020 Visible satellite images indicate that the area of disturbed weather moving across the central Caribbean Sea has developed a closed surface circulation, with the center embedded beneath cellular convective cells and a large cirrus canopy. Also, convection has increased in organization, and TAFB and SAB have given the system classification of T2.0/30 kt and T1.5/25 kt, respectively. Therefore, advisories are being initiated on Tropical Depression Fourteen with maximum winds of 30 kt. An expected ASCAT pass later today and an Air Force Reserve Hurricane Hunter mission scheduled for this afternoon should give us a better handle on both the depression's center location and its maximum winds. The depression continues to move westward at a pretty good clip, currently estimated to be on a heading of 280 degrees at 18 kt. This motion is being driven by the western extent of the Bermuda high, which currently noses into the northwestern Caribbean Sea. However, a deep-layer trough over the Gulf of Mexico is expected to become the main driver in the coming days, causing the cyclone to slow down and turn rather suddenly toward the west-northwest and northwest in the next 24-36 hours. A general northwestward motion should then continue until the end of the 5-day forecast period, bringing the system across the Yucatan Peninsula Saturday night and into the central and western Gulf of Mexico early next week. Most of the reliable track models are clustered close to one another, and the official NHC track forecast is therefore very close to the multi-model consensus aids, including the HCCA model. Once the depression slows down during the next 24-36 hours, environmental conditions appear ideal for strengthening. The magnitude of vertical shear is expected to be less than 10 kt for at least the next 2 days, while the system will be moving over the deep, warm waters of the northwestern Caribbean Sea, where sea surface temperatures are 29-30 degrees Celsius. Given these conditions, some of the intensity guidance actually appears more muted than I would have expected, and I have therefore elected to closely follow the SHIPS and LGEM models, which are near the upper end of the guidance envelope. It is possible that the depression could be near or at hurricane strength when it approaches the Yucatan Peninsula of Mexico in 2-3 days. Some weakening is anticipated when the center moves over land, and then re-strengthening is likely after it moves over the Gulf of Mexico. There will be an increase in shear over the Gulf in 4-5 days, and right now there is greater-than-normal uncertainty in how this will affect the cyclone's intensity at that point. For now, the official forecast on days 4 and 5 shows a flat-lined intensity, and this scenario lies a little above the ICON intensity consensus and the HCCA model solution. Key Messages: 1. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and it could produce tropical-storm-force winds and heavy rainfall over portions of the coast of Honduras and the Bay Islands beginning tonight through Friday. The system could be near or at hurricane strength when it reaches the Yucatan Peninsula of Mexico late Saturday, and watches could be required for a portion of that area later today. 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 20/1500Z 15.1N 79.7W 30 KT 35 MPH 12H 21/0000Z 15.5N 81.9W 35 KT 40 MPH 24H 21/1200Z 16.3N 84.2W 40 KT 45 MPH 36H 22/0000Z 17.1N 85.5W 50 KT 60 MPH 48H 22/1200Z 18.4N 86.4W 55 KT 65 MPH 60H 23/0000Z 19.9N 87.4W 60 KT 70 MPH 72H 23/1200Z 21.5N 88.9W 45 KT 50 MPH 96H 24/1200Z 25.0N 92.0W 50 KT 60 MPH 120H 25/1200Z 28.0N 94.0W 50 KT 60 MPH $$ Forecaster Berg
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