A tropical depression in the Gulf of Mexico strengthened into Tropical Storm Harold as it moved toward Texas early on Tuesday.

A Tropical Storm Warning was issued for the southern Texas coast, including Corpus Christi, after the storm strengthened at about 2 a.m. ET, according to the National Hurricane Center.

The storm's center was about 155 miles south-southeast off of Port Mansfield, Texas, as of 4 a.m. local time. It had been 180 miles offshore at about 2 a.m. local time, the National Weather Service station in Brownsville, Texas, said on Tuesday.

Downpours from the "far reaches of Harold lurk offshore early this morning," the station said.

Heavy rain, gusty winds and some coastal flooding is possible in southern Texas as Harold is expected to make landfall Tuesday morning south of Corpus Christi.

Residents of that coastal city were being urged to review their personal emergency response plans, government officials said on Monday.

"Along area beaches, the storm surge is expected to produce moderate coastal flooding through late Wednesday, with the potential for water to reach the dunes and beach access roads," the city's Emergency Operations Center said in a statement.

Very wet and stormy conditions were expected during Tuesday's commute in Corpus Christi, with about 3 inches of rain across the region on Tuesday and Wednesday, officials said. As much as 5 inches were expected in a few areas, the statement said.

"This rainfall could lead to areas of flash and urban flooding," the city said.

The highest rainfall is expected to be along the coast between Brownsville and Corpus Christi, the NWS Weather Prediction Center said Tuesday.

"The good news is that the bulk of this rainfall will be beneficial for the drought-stricken region, but too much rainfall too fast could lead to isolated to scattered instances of flash flooding," the center said.

This is a developing story. Please check for updates.