Tropical Depression Twenty Forms In The Far Eastern Atlantic, No Threat To T&T

From the 52nd tropical wave of the 2021 Atlantic Hurricane Season to move off the African Coast, Tropical Depression Twenty has formed, forecast to become Tropical Storm Victor within the next 24 hours.

Based on the current forecast, if Victor forms south of 9°N, only Kirk in 2018 has become an Atlantic named storm south of 9°N in the satellite era (1966 onwards). Kirk formed at 8.1°N.

By October 1st, Tropical Depression Twenty is forecast by the National Hurricane Center to become a hurricane. The 2021 Atlantic hurricane season has already had 7 hurricanes. 7 seasons in the satellite era (1966 onwards) have had 8+ Atlantic hurricanes by 1 October: 1969, 1995, 2004, 2005, 2012, 2017, 2020.

This depression is forecast to move into the North Atlantic Ocean without any direct threats to land. Tropical Depression Twenty, and eventual Victor, is not forecast to affect the Lesser Antilles, including Trinidad and Tobago. There are no alerts, watches, or warnings for T&T from the Trinidad and Tobago Meteorological Service at this time.

The Latest From The National Hurricane Center

Tropical Depression Twenty's Forecast Track as of 11:00 AM Wednesday 29th September 2021. (National Hurricane Center)
Tropical Depression Twenty’s Forecast Track as of 11:00 AM Wednesday 29th September 2021. (National Hurricane Center)

At 11:00 AM AST, the center of Tropical Depression Twenty was located near 8.3°N, 24.6°W. The depression is moving toward the west-northwest near 22 KM/H, and this motion is expected to continue during the next couple of days, followed by a turn to the northwest.

Maximum sustained winds are near 55 KM/H with higher gusts. Steady strengthening is forecast, and the depression is expected to become a tropical storm tonight and a hurricane in a couple of days. The estimated minimum central pressure is 1007 millibars.

Tropical Depression Twenty's latest information as of 11:00 AM Wednesday 28th September 2021. (National Hurricane Center)
Tropical Depression Twenty’s latest information as of 11:00 AM Wednesday 28th September 2021. (National Hurricane Center)

Tropical Depression Twenty’s Watches & Warnings

Tropical Depression Twenty's Watches and Warnings as of 11:00 AM Wednesday 29th September 2021. (National Hurricane Center)
Tropical Depression Twenty’s Watches and Warnings as of 11:00 AM Wednesday 29th September 2021. (National Hurricane Center)

There are no coastal watches or warnings in effect at this time. As this tropical cyclone gradually strengthens and moves into the North Atlantic, we’ll be monitoring for the possibility of long-period swells.

At this time, there are also no hazards affecting land.

Tropical Depression Twenty's probabilities for tropical-storm-force winds as of 11:00 AM Wednesday 29th September 2021. (National Hurricane Center)
Tropical Depression Twenty’s probabilities for tropical-storm-force winds as of 11:00 AM Wednesday 29th September 2021. (National Hurricane Center)

This system is of no direct threat to Trinidad and Tobago.

Tropical Depression Twenty’s Forecast Discussion

Tropical Depression Twenty (Weathernerds.org)

The area of low pressure located over the far eastern tropical Atlantic that NHC has been monitoring has now become a tropical depression, the twentieth tropical cyclone of the 2021 Atlantic hurricane season. Satellite images indicate that the system is producing a large area of showers and thunderstorms that have become fairly well organized around the center. An ASCAT-A pass from a few hours ago indicated that the system now has a well-defined circulation and that the radius of maximum wind is 30-40 n mi north of the center. The initial intensity is set at 30 kt based on the ASCAT data and the T2.0/30 kt Dvorak classifications from TAFB and SAB. The minimum pressure of 1007 mb is partially based on data from a ship report that passed near the depression.

Based on satellite fixes, the depression appears to be moving west-northwestward at about 12 kt. The system is currently located on the south side of a deep-layer ridge, and that feature should keep the cyclone on a west-northwest track during the next couple of days. After that time, the models show a mid- to upper-level low developing over the central tropical Atlantic, which erodes the western portion of the ridge. This change in the steering flow should cause the system to turn northwestward on Friday and then northward toward the end of the forecast period. Although the models generally agree on the evolution of the large-scale pattern, there are notable differences in the details, which leads to a fair amount of spread concerning when and where the turn to the north occurs. The GFS is farthest east while the ECMWF shows the westernmost solution. The NHC track forecast lies between those models and is near the TVCA multi-model consensus.

The depression is expected to remain in conducive environmental conditions for strengthening during the next 2 or 3 days. During that time period, the storm is forecast to move over 28-29 deg C waters while embedded within an airmass of high mid-level moisture and very low wind shear (less than 10 kt). Therefore, steady strengthening seems likely, and the NHC forecast brings the system to a tropical storm by tonight and a hurricane in a couple of days. Beyond a few days, however, the models show a pronounced increase in southwesterly shear and a notably drier atmosphere. These unfavorable conditions should end the opportunity for strengthening and promote a weakening trend. The NHC intensity forecast is a near a blend of the HCCA, IVCN, and IVDR consensus models.

Tropical Cyclone Climatology

2021 has already produced 20 tropical cyclones in the Atlantic Basin, with the next system being named Victor for the 2021 Atlantic Hurricane Season. For this time of year, most systems form in the Caribbean, the Gulf of Mexico, and off of the Eastern United States.

As we head through the last few days of September and into October, we’ll continue to monitor the entire Atlantic closely as tropical cyclones could form from tropical waves, non-tropical low-pressure systems in the North Atlantic, and from the Central America Gyre in the Western Caribbean Sea or the southwestern Gulf of Mexico.

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