Tropical Depression Twenty-Nine Forms In The Caribbean Sea

Tropical Depression Twenty-Nine has formed in the northwestern Caribbean Sea, becoming the 29th tropical cyclone for 2020. This system is forecast to strengthen into a tropical storm over the next 72 hours as it moves south of Jamaica.

Note that this system has not broken the 2005 record for the most tropical depressions (at 31, 2020 is at 29) or the most number of tropical storms (at 28, 2020 is at 27), at this time.

If this system strengthens into a tropical storm, it will be named Eta, becoming the earliest 28th named storm in Atlantic History, edging out 2005’s version of Zeta which formed on December 30th. This will be the first time Eta will be used in Atlantic history.

This tropical cyclone is not forecast to impact Trinidad, Tobago, or the Lesser Antilles. The tropical wave did produce floods, gusty winds, and landslides across parts of Barbados, St. Vincent, and St. Lucia over the past week.

List of names for the 2020 Atlantic Hurricane Season. The next named tropical cyclone will be called Eta.
List of names for the 2020 Atlantic Hurricane Season. The next named tropical cyclone will be called Eta.
List of Greek names for the Atlantic Hurricane Season. The next named tropical cyclone will be called Eta.
List of Greek names for the Atlantic Hurricane Season. The next named tropical cyclone will be called Eta.

At 5:00 PM AST, the center of Tropical Depression Twenty-Nine was located near latitude 15.0 North, longitude 73.2 West. The depression is moving toward the west near 15 mph (24 km/h), and this westward motion is expected to continue through Sunday night. A slower motion toward the west-southwest and then southwest is forecast on Monday and Tuesday. On the forecast track, the center of the cyclone is expected to be near the northeastern coast of Nicaragua by Monday night.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts. Strengthening is forecast, and the depression is expected to become a tropical storm tonight. The system is then expected to become a hurricane by Monday. The estimated minimum central pressure is 1006 millibars.

Tropical Depression Twenty-Nine Forecast Track as of 5:00 PM AST Saturday 31st October 2020. (National Hurricane Center)
Tropical Depression Twenty-Nine Forecast Track as of 5:00 PM AST Saturday 31st October 2020. (National Hurricane Center)

Watches & Warnings

Tropical Depression Twenty-Nine Watches and Warnings as of 5:00 PM AST Saturday 31st October 2020. (National Hurricane Center)
Tropical Depression Twenty-Nine Watches and Warnings as of 5:00 PM AST Saturday 31st October 2020. (National Hurricane Center)

There are no coastal watches or warnings in effect.

Interests in Nicaragua and Honduras should monitor the progress of the depression. Hurricane or tropical storm watches will likely be required for portions of these countries later tonight or early Sunday.

Hazards Affecting Land

Tropical Depression Twenty-Nine probabilities for tropical-storm-force winds as of 5:00 PM AST Saturday 31st October 2020, as well as the most likely time of arrival of tropical-storm-force winds. (National Hurricane Center)
Tropical Depression Twenty-Nine probabilities for tropical-storm-force winds as of 5:00 PM AST Saturday 31st October 2020, as well as the most likely time of arrival of tropical-storm-force winds. (National Hurricane Center)

RAINFALL: Through Thursday afternoon, the depression is expected to cause 5 to 10 inches of rain, with local 15-inch amounts, across Jamaica, the Cayman Islands, and possibly the southern coast of Hispaniola. Across portions of Central America, 10 to 15 inches of rain, with local amounts to 25 inches are expected. This rainfall should lead to flash flooding and river flooding and could cause landslides in areas of higher terrain.

This system is of no direct threat to the Windward Islands, including Trinidad and Tobago.

Tropical Depression Twenty-Nine Forecast Discussion

Tropical Depression Twenty Nine (Weathernerds.org)
Tropical Depression Twenty Nine (Weathernerds.org)

Showers and thunderstorms have continued to become better organized in association with a tropical wave that 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 discussion by NHC Forecaster Berg.

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