(Adds detail on Chris, disturbance in Gulf of Mexico)

MIAMI, June 21 (Reuters) - Tropical Storm Chris strengthened in the North Atlantic off Newfoundland on Thursday, becoming the season's first Atlantic hurricane, forecasters at the U.S. National Hurricane Center said.

Chris had top winds of 75 miles per hour (120 km per hour) and was about 625 miles (1,005 km) southeast of Cape Race, Newfoundland. It posed no threat to land, forecasters said.

Chris formed unusually far north for an early season hurricane, and was expected to make a slow loop before weakening over cooler waters during the weekend.

Forecasters also kept watch on a low pressure area associated with a broad mass of thunderstorms in the southeastern Gulf of Mexico and northwestern Caribbean.

It had a 30 percent chance of developing into a tropical depression or tropical storm in the next couple of days, the forecasters said. That system soaked southern Florida and could bring heavy rain and flooding to Mexico's Yucatan Peninsula and western Cuba, the forecasters said.

It was too early to know whether the system would threaten energy interests clustered in the northern Gulf of Mexico.

The Atlantic hurricane season runs from June 1 to Nov. 30, but got off to an early start this year. Tropical Storm Alberto quickly fizzled off South Carolina and Tropical Storm Beryl soaked the southeastern United States in May.

The U.S. National Oceanic and Atmospheric Administration predicted there would be nine to 15 tropical storms in the Atlantic basin this year, with four to eight strengthening into hurricanes.

(Reporting By Jane Sutton; Editing by Vicki Allen)

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