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Chill falls over the Atlantic as the official season heads towards close
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| #1013097 (Received by flhurricane at: 4:59 AM 21.Aug.2020) TCDAT3 Tropical Depression Thirteen Discussion Number 6 NWS National Hurricane Center Miami FL AL132020 500 AM AST Fri Aug 21 2020 Tropical Depression Thirteen remains very disorganized this morning. The associated convection is elongated from northwest to southeast, and the low-level center is located near the northwestern end of the convective area. Additionally, satellite imagery and model analyses indicate that the mid-level center is located several hundred miles to the southeast of the low-level center. Earlier aircraft and scatterometer data suggested the possibility that the system was an open wave. However, the currently available data is ambiguous on whether the system still has a closed circulation, so it will be maintained as a tropical depression. The initial intensity remains 30 kt. The initial motion is west-northwestward or 285/18 kt. There is little change to the track forecast philosophy through about 96 h. A strong subtropical ridge over the western Atlantic should remain north of the depression during the next few days, steering the cyclone at a fast pace to the west-northwest. After that, the ridge weakens some over the eastern Gulf of Mexico, and Tropical Depression Thirteen may interact with Tropical Depression Fourteen, which is also forecast to be in the Gulf by that time, with the result of these things being a turn toward the northwest or north-northwest. The track guidance has shifted southward since the last advisory, with the UKMET shifting far enough to the south that it takes the system over the Caribbean south of Cuba. The new forecast track is also shifted a bit southward from the previous track. However, it lies to the north of the GFS, the UKMET, and the various consensus models. It also lies north of the ECMWF model from 24-72 h. The intensity forecast remains low confidence. The separation between the low- and mid-level centers, as well as some westerly shear and dry air entrainment, suggests that significant strengthening is unlikely during the next 24 h or so. The dynamical models suggests the centers will become more vertically aligned around 36-48 h and that the shear should diminish. However, the system could be close to Hispaniola during this time, and be near Cuba thereafter, especially if it moves south of the forecast track. The upper-level winds over the Gulf of Mexico should be generally favorable for development if the cyclone doesn`t get too close to Tropical Depression Fourteen. The possibilities range from the system degenerating to an open wave as seen in the GFS and ECMWF to a major hurricane as seen in the HWRF. Given the uncertainty, the intensity forecast is unchanged from the previous advisory, and it lies a little below the intensity consensus. Key Messages: 1. Tropical storm conditions are possible across portions of the northern Leeward Islands, the Virgin Islands, Puerto Rico, the southeastern Bahamas, and the Turks and Caicos islands later today through Saturday night, and Tropical Storm Watches have been issued for some of these islands. Heavy rainfall is likely across this area beginning today and could cause mudslides and flash and urban flooding through Sunday. 2. The details of the long-range track and intensity forecasts are more uncertain than usual since the system could move over portions of the Greater Antilles this weekend. However, this system could bring some storm surge, rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida this weekend and early next week. Interests there should monitor this system`s progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 17.8N 58.5W 30 KT 35 MPH 12H 21/1800Z 18.1N 60.7W 30 KT 35 MPH 24H 22/0600Z 18.8N 64.0W 35 KT 40 MPH 36H 22/1800Z 19.7N 67.5W 40 KT 45 MPH 48H 23/0600Z 20.6N 71.1W 45 KT 50 MPH 60H 23/1800Z 21.8N 74.9W 50 KT 60 MPH 72H 24/0600Z 23.2N 78.5W 55 KT 65 MPH 96H 25/0600Z 26.5N 84.0W 65 KT 75 MPH 120H 26/0600Z 30.0N 87.0W 65 KT 75 MPH $$ Forecaster Beven |
