Tropical storm Hanna has been upgraded to a hurricane as it moved toward the Texas coast and threatened to bring heavy rain, storm surges and possible tornadoes.

Hanna is the first hurricane of the 2020 Atlantic season, the US National Hurricane Centre said.

Maximum sustained winds had increased to 75 mph with the storm centred about 100 miles east-southeast of Corpus Christi in Texas and moving towards land at 9mph.

A storm surge warning of up to 5 feet in effect from Baffin Bay to Sargent was extended south of the bay to Port Mansfield, Texas, with people advised to protect life and property from high water.

Tornadoes were also possible on Saturday for parts of the lower to middle Texas coastal plain, forecasters said.

Meanwhile, tropical storm Gonzalo was still on track to move across the southern Windward Islands on Saturday afternoon or evening.

Gonzalo was moving west at nearly 18mph with maximum sustained winds at 40 mph, the National Hurricane Centre said on Saturday morning.

Tropical Weather-Texas
A sign reading Hurricane Warning Corpus Christi as Storm Hanna approaches (Courtney Sacco/Corpus Christi Caller-Times via AP)

A tropical storm warning remained for St Vincent and the Grenadines, Tobago and Grenada and its dependencies, with the weather system expected to dissipate by Sunday night or Monday.

Gonzalo and Hanna broke the record for the earliest seventh and eighth Atlantic named storms, respectively, according to Colorado State University hurricane researcher Phil Klotzbach.

The previous records were Gert on July 24, 2005, and Harvey on August 3, 2005, Mr Klotzbach said.

Cristobal, Danielle, Edouard and Fay also set records for being the earliest named Atlantic storm for their alphabetic order.