The first named storm of the hurricane season is taking aim at Texas and Mexico, threatening the Gulf Coast with severe flooding and high winds.

Tropical Storm Alberto formed over the western Gulf of Mexico on Wednesday morning and is expected to reach Mexico’s Gulf coast early Thursday, according to the National Hurricane Center.

The storm is large, with tropical-storm-force winds extending 415 miles from its center.

A tropical storm warning is in effect for the northeastern coast of Mexico as well as part of Texas coast from the mouth of the Rio Grande up to San Luis Pass. High winds and as much as 10 to 15 inches of rain are expected in Corpus Christi.

Gov. Greg Abbott issued a disaster declaration for 51 Texas counties “to ensure Texans and at-risk regions have the resources and personnel needed to respond to this storm,” he said in a statement.

With maximum sustained winds near 40 miles per hour, the storm is expected to strengthen slightly as it approaches land, then weaken rapidly once its center moves inland.

Alberto was about 305 miles southeast of Brownsville, Texas, traveling about 9 miles per hour, as of around 4 p.m. local time, officials said.

The National Hurricane Center said tornadoes were possible Wednesday across parts of Texas. Up to 10 inches of rain is expected across northeast Mexico and South Texas. Some parts of Mexico, including Coahuila, Nuevo Leon, and Tamaulipas, could see up to 20 inches.

The National Weather Service office in Houston said at 4:30 a.m. local time that there had already been reports of coastal flooding as rain moved inland.

“The disturbance is very large, with rainfall, coastal flooding and wind impacts likely to occur far from the center along the coasts of Texas and northeastern Mexico,” the National Hurricane Center said in an update.

The hurricane center also said early Wednesday that life-threatening mudslides were likely in higher areas of northern Mexico, including around the cities of Monterrey and Ciudad Victoria.

The Texas A&M Forest Service has mobilized four teams comprised of 100 personnel and 24 vehicles, while the Texas National Guard has three platoons of more than 40 personnel in total, alongside 20 vehicles, including Chinook helicopters.

The weather service told people in the affected areas to have five to seven days’ supplies of food, water and other necessities.

The storm warning came as 71 million people were under some form of heat advisory on Wednesday, as a severe heat wave is set to last through Friday.

This article was originally published on NBCNews.com