UPDATE: Arlene has been downgraded to a post-tropical cyclone. No further advisories will be issued.
Tropical Storm Arlene has developed, becoming the first tropical storm of the 2017 Atlantic hurricane season.
Arlene first formed on Wednesday as a sub-tropical depression, but gradually strengthened and took on more tropical characteristics with winds of 45 mph.
Tropical storm formation over the Atlantic basin is very rare during the months of January, February, March and April. There has been only one tropical storm on record during April from 1851 to 2016, according to the Atlantic Oceanographic and Meteorological Laboratory.
The system migrated from part tropical and part subtropical to a fully tropical system on Thursday morning just a few hours before becoming a tropical storm.
A tropical storm has winds ranging from 39 to 73 mph that rotate around a well-organized center that contains showers and thunderstorms.
Tropical Storm Arlene will not pose a threat to the U.S. coast.
The Atlantic Hurricane Season officially starts June 1.