Millions of people along the southern coast of Texas were under severe weather advisories as officials warned of high storm surge, torrential rain and possible tornadoes as Tropical Storm Alberto barreled over northern Mexico.

The first named storm in the 2024 Atlantic hurricane season made landfall in Mexico sometime between 4 a.m. and 7 a.m. local time, according to the National Hurricane Center. Along with sustained winds near 45 mph, the storm is forecast to dump up to 20 inches across parts of northeast Mexico with nearly a foot of rain expected throughout southern Texas.

Such high rainfall totals will likely produce “considerable flash flooding and urban flooding” as well as possible mudslides across northern Mexico, the NHC said.

After making landfall, Alberto is expected to diminish in strength, though it could still produce life-threatening weather conditions.

Alberto began drenching southern Texas on Wednesday, triggering widespread coastal flooding that left Surfside Beach, a city along the Texas Gulf Coast south of Houston, under several feet of water. The storm also lashed Mexico with heavy rain, and caused the deaths of at least three minors, Nuevo Leon state Governor Samuel Garcia told local media without providing details.

Across southern Texas, the combination of storm surge and high tide is raising alarms on Thursday as floodwaters could reach up to 4 feet along the coast. The deepest waters will breach the shore along the Texas coast just to the north of Mexico, where the surge will be accompanied by large and dangerous waves, according to NHC.

Life-threatening surf and rip current conditions are among the central threats for the Gulf Coast of Texas through Friday. In deep South Texas, multiple counties were under a tornado watch as forecasters warned that a possible tornado or two could spin up through the morning.

Flood advisories were also active. Multiple south-central counties received 1 and 3 inches of rain by 2 a.m. Thursday, the weather service office in Corpus Christy said, adding: “Flash flooding is ongoing or expected to begin shortly.”

Gov. Greg Abbott issued a disaster declaration for 51 counties and activated three platoons of the Texas National Guard, including more than 40 personnel, 20 vehicles and Chinook helicopters.

Tropical Storm Alberto is kicking off what experts have said will be a busy storm season. National Oceanic and Atmospheric Administration Director Rick Spinrad said last month that the Atlantic hurricane season is shaping up to be “extraordinary,” with an “85% chance for an above-average year.”

Tropical Storm Alberto tracker

Contributing: Reuters; Doyle Rice, John Bacon, Kirsten Crow, USA TODAY

This article originally appeared on USA TODAY: Tropical Storm Alberto makes landfall; Texas braces for deluge