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Tropical Storm Dolly becomes 2nd earliest D-named storm in Atlantic

Subtropical Depression Four strengthened into Tropical Storm Dolly well off of the northeastern United States coast on Tuesday

Subtropical Depression Four strengthened into Tropical Storm Dolly well off of the northeastern United States coast on Tuesday. Not only did Dolly become a rare June D-named storm, only the third in recorded history, but it also will go down in the history books as the second-earliest fourth-named storm in the basin.

The storm's maximum sustained winds strengthened to 45 mph Tuesday, while it churned offshore of the East Coast, about 370 miles south of Nova Scotia, according to the National Hurricane Center (NHC).

The system managed to strengthen over water that is warm enough to support tropical development, according AccuWeather's Top Hurricane Expert Dan Kottlowski. The threshold that forecasters look for in order for tropical systems to develop or survive is 80 degrees Fahrenheit.

There was only a small window of opportunity for Dolly to develop as the system is expected to move over cooler water later on Tuesday, according to AccuWeather Meteorologist Mary Gilbert.

Credit: RAMMB-Satellite
Subtropical Depression Four was seen spinning east of the mid-Atlantic on June 22, 2020 before it strengthened into Dolly around midday.

Dolly will not pose any threat to land, and its lifespan will be extremely short.

The disturbance is expected to pass well to the south and east of Nova Scotia Tuesday afternoon and night, according to Kottlowski. Even though it will remain out to sea over its lifetime, it could stir rough seas and cause disruptions in the path of shipping interests.

It is extremely rare to have four named tropical storms by the end of June. According to records from the NHC, the month of June has only produced two other D-named storms: Tropical Storm Debby from 2012 and Tropical Storm Danielle from 2016.

Debby formed over the south-central Gulf of Mexico before slamming into the Big Bend area of Florida on June 26, 2012. The system weakened soon after moving inland, but it produced a considerable amount of flooding across northern and central portions of the state. Danielle formed in a similar area and was a short-lived tropical storm that developed over the southwestern Gulf of Mexico. The weak tropical storm made landfall near Tamiahua in eastern Mexico on June 20, 2016.

According to AccuWeather Senior Weather Editor and Meteorologist Jesse Ferrell, there have been 69 D-named storms in the Atlantic since storms were officially named starting in 1950. The most common of those names are Dolly at eight times and the aforementioned Debby and Danielle at seven times apiece.

Danielle's formation on June 20, 2016, just prior to landfall still holds the record for the earliest formation of the fourth tropical storm of the season.

So far, eight D-named storms have been retired, including Hurricane Diane in 1955 and Hurricane Dean in 2007. Hurricane Dorian from 2019 is expected to be retired sometime this year. Ferrell said all of the retired D-named storms formed in August, with the exception of Dennis, which formed the earliest on July 4, 2005.

The 2020 Atlantic hurricane season experienced its earliest third-named storm on record when Cristobal formed near the coast of southeastern Mexico on June 2.

The remainder of the Atlantic Ocean is quiet due to an "abnormally" large dust cloud spanning most of the basin and the presence of strong wind shear, or increasing winds with altitude.

Additional reporting by meteorologist Maura Kelly, staff writer Mark Puleo, and weather editor Jesse Ferrell.