Tropical storm Danielle formed Monday off the east coast of Mexico, US weather experts said. It was the fourth named storm of the season.
"Tropical storm Danielle is the earliest fourth tropical storm on record in (the) Atlantic basin," the Miami-based National Hurricane Center said.
The previous record was held by Tropical Storm Debbie, which formed in June 2012.
Danielle was not expected to develop into a hurricane over the next five days.
With maximum sustained winds of 47 miles (75 kilometers) per hour, Danielle was 75 miles southeast of Tuxpan, Mexico, the hurricane center said.
The storm is traveling in a westerly direction at a speed of about seven miles per hour.
A tropical storm warning was posted for a stretch of the Mexican coast from Laguna Verde to the Panuco river.
The Atlantic hurricane season runs from June 1 to November 30, but this year the season's first hurricane, Alex, formed in January, an unusual event.
The period between the end of May and the beginning of June saw the formation of Tropical Storms Bonnie and Colin, which did not become hurricanes.
