Tropical Depression Eleven Forms In The Atlantic

Tropical Depression Eleven has formed in the Central Atlantic after being tracked as INVEST 95L over the last few days. It is forecast to move just north of the Leeward Islands this weekend as a tropical storm. Based on the forecast track, this would result in minimal impacts to T&T, though its associated tropical wave will bring showers and thunderstorms to T&T beginning on Friday through Sunday.

It is forecast to become a tropical storm Wednesday night. If it gets named, it would be Josephine. Current earliest Atlantic ‘J’ storm on record is Jose on Aug 22, 2005

At 5:00 PM AST, the center of Tropical Depression Eleven was located near latitude 11.7 North, longitude 40.0 West. The depression is moving toward the west near 16 MPH (26 KM/H), and this general motion is expected to continue through Wednesday. A west-northwestward motion at a similar forward speed is forecast to begin Wednesday night and continue through the rest of the week.

Maximum sustained winds are near 35 MPH (55 KM/H) with higher gusts. Some strengthening is forecast during the next 48 hours, and the depression is expected to become a tropical storm by Wednesday night. The estimated minimum central pressure is 1007 millibars.

Tropical Depression Eleven Forecast Track as of 5:00 PM AST Tuesday 11th August 2020. (National Hurricane Center)
Tropical Depression Eleven Forecast Track as of 5:00 PM AST Tuesday 11th August 2020. (National Hurricane Center)

Watches & Warnings

Tropical Depression Eleven Watches and Warnings as of 5:00 PM AST Tuesday 11th August 2020. (National Hurricane Center)
Tropical Depression Eleven Watches and Warnings as of 5:00 PM AST Tuesday 11th August 2020. (National Hurricane Center)

There are no alerts, watches or warnings in effect from the NHC for coastal areas.

Hazards Affecting Land

Tropical Depression Eleven probabilities for tropical-storm-force winds as of 5:00 PM AST Tuesday 11th August 2020, as well as the most likely time of arrival of tropical-storm-force winds. (National Hurricane Center)
Tropical Depression Eleven probabilities for tropical-storm-force winds as of 5:00 PM AST Tuesday 11th August 2020, as well as the most likely time of arrival of tropical-storm-force winds. (National Hurricane Center)

There are no hazards affecting land at this time.

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

Tropical Depression Eleven Forecast Discussion

Tropical Depression Eleven, well east of T&T and the Windward Islands (Weathernerds)
Tropical Depression Eleven, well east of T&T and the Windward Islands (Weathernerds)

Visible satellite imagery and ASCAT-C data from earlier in the day have shown that the area of low-pressure NHC has been monitoring over the tropical Atlantic has developed a less-elongated circulation with a well-defined center. For the most part, deep convection has persisted with the system since about this time yesterday, save a brief period of warming cloud tops this morning. The low now meets the criteria of a tropical cyclone, and advisories have been initiated on Tropical Depression Eleven with 30-kt winds, in line with the latest Dvorak Current Intensity numbers from TAFB and SAB.

The depression is moving westward, or 280/14 kt, to the south of a large mid-tropospheric high centered over the central Atlantic. This pattern is expected to evolve rather quickly, with a break developing in the ridge over the central Atlantic by 48 hours. This change should allow the depression to begin making more poleward progress, moving west-northwestward from 36 hours until the end of the forecast period. The track models are in good agreement on this scenario, as well as the system’s forward speed, and bring the center of the cyclone near or just to the north of the northern Leeward Islands in 4-5 days. This first NHC forecast lies just to the north of the multi-model consensus cluster through day 3, out of respect for the northern-lying ECMWF model, and then is close to HCCA on days 4 and 5.

Conventional satellite imagery and Saharan Air Layer analyses suggest that the center of the depression is being shielded from much drier air to its north and west. However, as has been the case for a few days, at least 15 kt of easterly shear has been pushing deep convection to the western side of the circulation. This shear is expected to decrease over the next day or two, which should allow for gradual strengthening to begin by 36 hours, and a peak in the cyclone’s intensity should occur in about 3 days.

For this period, the NHC intensity forecast is a little above HCCA and the IVCN intensity consensus. After that time, westerly or southwesterly shear is forecast to develop and increase to 20-30 kt by days 4 and 5, which is likely to induce significant weakening. In fact, it’s notable that the conditions become hostile enough that the global models are showing the system opening up into a trough near the northern Leeward Islands by day 5, which is a plausible alternate scenario.

Forecast Discussion by Forecaster Berg from the NHC.

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