First tropical depression forms

The first tropical storm of the 2017 season has formed in the north Atlantic, in what is a rare event for one of these systems to happen this early in the year.

Tropical storm Arlene formed over the open waters of the Atlantic Ocean Thursday afternoon. Tropical storm-force winds extended out 105 miles from its center. Forecasters expect the storm to dissipate sometime on Friday.

Forecasters say the storm - only the second tropical storm on record in the Atlantic during the month of April - is very far out in the ocean and poses no threat to land. Tropical Storm Colin waited until the official start of the season when it was named June 5.

Arlene is the first April Atlantic Basin system since 2003, and its formation by no means is an indicator as to whether the tropics will be busy or not later this summer and fall. In fact, early forecasts suggest the 2017 season will be just below average in terms of the number of storms expected. Therefore, it was declared that it transitioned from a subtropical depression to a tropical depression Thursday morning.

"If El Niño fails to launch, we may be too low with our numbers", said Todd Crawford, chief meteorologist with the Weather Company, an IBM Corp business, which forecast 12 named storms, four hurricanes and two major hurricanes.

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While a subtropical storm shares some features with the more familiar tropical systems, there are some key differences. Tropical storms in April surely emerged before satellite monitoring, but they probably went unnoticed, according to Phil Klotzbach, a hurricane researcher at Colorado State University. The 2016 season got a jump-start when Hurricane Alex formed january 14. The depression became Tropical Storm Arlene later in the day.

A subtropical depression or storm exhibits features of both tropical and non-tropical systems.

"A non-tropical storm will sweep in prior to the end of the week and should create a more hostile atmosphere for strengthening", Kottlowski said.

As a result, the strongest winds and rain become closer to the center and, with time, further intensification becomes possible.

  • Toni Ryan