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MIAMI — Tropical Storm Harvey regained strength as it drifted in the Gulf of Mexico toward Texas early Thursday and forecasters said those in its path must start preparing for the storm to potentially become a hurricane before it even makes landfall.

A hurricane warning was issued for the Texas coast Thursday morning, covering an area from Port Mansfield to Matagorda.

Louisiana could also experience a dangerous combination of rainfall and storm-surge this weekend or early next week, according to Weather.com.

In a first for the National Hurricane Center, a public storm surge warning has been issued for long swaths of the Texas coast.

Warnings extend as far inland as Houston, Texas and Galveston, Texas.

Harvey could produce 10 to 15 inches of rain over the Texas coast and southwest Louisiana. Some areas could see as much as 20 inches.

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The storm's maximum sustained winds had increased to near 45 mph. The NHC said additional strengthening was expected and Harvey could become a hurricane by Friday, when it's expected to approach the southern Texas coast.

As of 5 a.m. EDT, the storm was centered about 370 miles southeast of Port Mansfield and was moving north near 10 mph.

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In Texas, Gov. Greg Abbott has ordered the State Operations Center to elevate its readiness level, making state resources available for possible rescue and recovery actions. Abbott also pre-emptively declared a state of disaster for 30 counties on or near the coast to speed deployment of state resources to any areas affected.

Harvey "poses a threat of imminent disaster, including severe flooding, storm surge and damaging winds," Abbott's statement said.

Emergency officials Wednesday asked residents along the upper Texas coastline to move or prepare to move inland. Those in low-lying areas were urged to seek higher ground, and those elsewhere were told to monitor official announcements closely.

Chris Mathew fills his vehicle and five gas cans at Costco in preparation for tropical weather on Aug. 23, 2017, in Pearland, Texas. Steve Gonzales / Houston Chronicle via AP

"Now is the time to check your emergency plan and take necessary actions to secure your home or business. Deliberate efforts should be underway to protect life and property," the weather service said in an statement early on Thursday.

On South Padre Island, people filled sandbags and loaded them into cars and vans Wednesday to take to protect exposed homes and businesses.

Texas A&M University-Corpus Christi issued a mandatory evacuation to all students who live on campus and canceled events.

Royal Dutch Shell, Anadarko Petroleum and Exxon Mobil announced on Wednesday they were curbing some oil and gas output at facilities in the Gulf of Mexico ahead of the storm.

Others in the forecast path of the storm sought out generators, plywood and other goods from hardware stores.

Meanwhile, rice farmers in coastal Matagorda County moved quickly to harvest their crops.