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| #1023455 (Received by flhurricane at: 4:53 PM 31.Oct.2020) TCDAT4 Tropical Depression Twenty-Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL292020 500 PM EDT Sat Oct 31 2020 Showers and thunderstorms have continued to become better organized in association with a tropical wave which has been moving westward across the central Caribbean Sea. It was unclear this morning if the system had developed a closed low-level circulation, since scatterometers have avoided the system over the past 24 hours, but recent visible and microwave satellite images suggest that the system almost certainly now has a well-defined center. For that reason, the system is being designated as a tropical depression with 30-kt winds, based on Dvorak classifications of T2.0 from both TAFB and SAB. A low- to mid-level ridge axis that extends from the subtropical Atlantic southwestward to Cuba and the Bahamas is currently steering the depression toward the west (270 degrees) at an estimated speed of 13 kt. Model guidance is in fairly good agreement on the depression's future track for the first 48 hours or so. The cyclone is expected to continue westward for the first 36 hours and then slow down and turn west-southwestward by 48 hours as it approaches the coasts of Nicaragua and Honduras, in response to a building ridge over the Gulf of Mexico. After that time, however, there is significant divergence in the models. For example, the ECWMF and its ensemble members continue on a faster westward motion across Central America, while the GFS and its ensemble members stall the system over the western Caribbean Sea through day 5. Given this discrepancy, the NHC official track forecast shows a slow motion on days 3 through 5, and brings the cyclone's center slowly across northern Nicaragua, more or less in line with the multi-model consensus aids. This forecast is of generally low confidence, however, and significant changes could be required in later advisory packages depending on model trends. The waters over the Caribbean Sea remain very warm--around 29 degrees Celsius--and the environment is characterized by low vertical shear of 10 kt or less. Along with plenty of ambient moisture, these parameters suggest the system is primed for steady, if not significant, strengthening during the next few days. The NHC official forecast generally lies between the SHIPS guidance and the HCCA corrected-consensus aid, which lie near the upper bound of the intensity guidance, and it brings the system to hurricane strength in 48 hours. The intensity forecast hinges greatly on whether or not the cyclone's center moves inland over Central America, but regardless, the system is expected to be a hurricane when it approaches the Honduras and Nicaragua coasts in a few days. Key Messages: 1. The depression is expected to strengthen to a hurricane early next week as it approaches the coast of Central America late Monday and Monday night, and there is a risk of storm surge, hurricane-force winds, and heavy rainfall for portions of Nicaragua and Honduras. Hurricane Watches could be needed for portions of those areas later tonight. 2. Through Thursday afternoon, heavy rainfall from the system will likely lead to flash flooding and river flooding across portions of Jamaica, the Cayman Islands, and Central America, which could result in landslides in areas of higher terrain. Flooding is also possible near the southern coast of Hispaniola. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 15.0N 73.2W 30 KT 35 MPH 12H 01/0600Z 15.1N 75.6W 35 KT 40 MPH 24H 01/1800Z 15.4N 78.3W 45 KT 50 MPH 36H 02/0600Z 15.5N 80.4W 55 KT 65 MPH 48H 02/1800Z 15.1N 82.1W 65 KT 75 MPH 60H 03/0600Z 14.3N 83.1W 75 KT 85 MPH 72H 03/1800Z 13.8N 83.7W 70 KT 80 MPH...INLAND 96H 04/1800Z 13.5N 85.5W 40 KT 45 MPH...INLAND 120H 05/1800Z 14.0N 86.9W 25 KT 30 MPH...INLAND $$ Forecaster Berg |
