Subtropical Depression Four Forms, Forecast to be named Dolly by Tuesday

At 5:00 PM AST, the center of Subtropical Depression Four was located near latitude 38.2 North, longitude 65.7 West.

The subtropical depression is moving toward the east-northeast near 9 MPH (15 KM/H) and this motion is forecast to continue through tonight. A motion toward the northeast is expected on Tuesday and Wednesday.

Maximum sustained winds are near 35 MPH (55 KM/H) with higher gusts. Some slight strengthening is possible tonight and early Tuesday, and the subtropical depression could briefly become a subtropical storm. Slow weakening is expected to begin by Tuesday afternoon or evening.

The earliest 4th Atlantic named storm on record is Danielle (6/20/2016), with Debby at the 2nd earliest (6/23/2012 at 12 UTC). Subtropical Depression Four forecast to be named in 12 hours – which would make it 2nd earliest on record.

The estimated minimum central pressure is 1009 millibars.

Subtropical Depression Four Forecast Cone as of 5:00 PM AST Monday 22nd June 2020. Credit: National Hurricane Center
Subtropical Depression Four Forecast Cone as of 5:00 PM AST Monday 22nd June 2020. Credit: National Hurricane Center

Watches & Warnings

Subtropical Depression Four Watches and Warnings as of 5:00 PM AST Monday 22nd June 2020. Credit: National Hurricane Center

There are no watches or warnings in effect, as this system moves into the North Atlantic Ocean, away from land masses.

Hazards Affecting Land

Subtropical Depression Four as of 5:00 PM AST Monday 22nd June 2020. (Weathernerds)
Subtropical Depression Four as of 5:00 PM AST Monday 22nd June 2020. (Weathernerds)

There are no hazards affecting land at this time.

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

Subtropical Depression Four Forecast Discussion

The non-tropical low-pressure system that the National Hurricane Center has been following for the past couple of days off of the U.S. east coast has developed enough organized convection near the center to be classified as a subtropical depression. The subtropical status is due to the low-level circulation center being co-located beneath an upper-level cold low as seen in water vapor imagery. The initial intensity of 30 kt is based on earlier ASCAT wind data indicating numerous surface wind vectors of 26-28 kt in the southern semicircle, along with a TAFB subtropical satellite classification of ST1.5/25-30 kt.

The initial motion estimate is 075/08 kt. Subtropical Depression Four is located north of a deep-layer ridge and is being influenced by weak westerly mid- to upper-level flow. The cyclone is forecast by all of the global and regional models to move east-northeastward tonight and then turn northeastward on Tuesday. A northeastward motion at a faster forward speed is expected Tuesday night through Thursday when the system is forecast to be located over the cold waters of the far north Atlantic. The cyclone should be absorbed by a larger extratropical low or dissipate on Thursday. The NHC track forecast is close to a blend of the simple consensus aids TVCN and GFEX and the NOAA-HCCA corrected consensus.

The cyclone is beginning to move over a ridge of higher SSTs of 26.0-26.5 deg C in the northern extent of the Gulf Stream. The forecast track takes the subtropical depression down the length of the axis of warmer water during the next 12-18 h, so there is the potential for the cyclone to become a subtropical storm during that time, especially given the large pool of cold air aloft, with 200-mb temperatures of near -58 deg C and 500-mb temperatures of about -10 deg C which is creating a lot of instability. After the system moves off of the warm ridge and into sharply cooler water around 36 hours or so, gradual weakening is expected, with a transition to an extratropical cyclone forecast by 48 hours. The NHC intensity forecast closely follows a blend of the consensus models ICON, IVCN, and HCCA.

Forecast Discussion by Forecaster Stewart from the NHC.

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