Rescue workers were activated in southern Texas in preparation for heavy rain expected to accompany a tropical depression slowly churning its way through the Gulf of Mexico.

The fifth depression of the Atlantic hurricane season formed late Tuesday and was expected to become a tropical storm before making landfall in Texas on Thursday morning, the National Weather Service said.

At 7 a.m. CDT Wednesday, the depression was centered 275 miles east-southeast of Brownsville, Texas, and about 310 miles east of La Pesca, Mexico, according to the National Hurricane Center in Miami. Forecasters at the center said the depression appeared to be moving to the west-northwest around 13 mph.

Its maximum sustained wind speeds were near 30 mph and gusting, and forecasters said it was expected to strengthen. If its wind speeds reach the 39-mph threshold for a tropical storm, it would be named Erin.

The National Hurricane Center issued a tropical storm watch for the Texas coast from Freeport, south of Houston, southward to the border. The government of Mexico issued a tropical storm watch for the northwest coast of Mexico from Rio San Fernando northward.

A tropical storm watch means that tropical storm conditions are possible within 36 hours.

Gov. Rick Perry said he was sending emergency vehicles and personnel to southern Texas in advance of the weather system.

“Because storms have saturated much of our state this summer, many communities in this storm’s projected path are at high risk of dangerous flash flooding,” Perry said in a statement hours before the tropical storm watch was issued.

He said he was sending 30 vehicles and 60 Texas National Guard members to Weslaco and San Antonio, was activating three helicopter rescue swimmer teams and was putting six teams on standby. Volunteer organizations were being prepared to provide mass care support.

National Weather Service forecaster Tim Speece said the system could bring heavy rains as far north as Victoria and as far inland as the Hill Country.

Meanwhile, Tropical Storm Dean got a little stronger late Tuesday in the Atlantic but remained far from land early Wednesday, forecasters said.

At 5 a.m. EDT, the storm was centered about 1,170 miles east of the Lesser Antilles in the Caribbean. It had top sustained winds of 50 mph, up from 40 mph on Tuesday. Some strengthening was expected within the next day.

Dean was moving over increasingly warmer waters, where atmospheric conditions could create a favorable environment for intensification into a hurricane by Friday, forecasters said. It was cruising west at about 18 mph. Forecasters said it was too early to tell where Dean will go.

Hurricanes have sustained winds of at least 74 mph.

Hurricane forecasters expect this year’s Atlantic hurricane season to be busier than average. Last week, they said as many as 16 tropical storms were likely to form, with nine strengthening into hurricanes.

The season runs from June 1 to Nov. 30, but August typically marks the start of the most active period. Ten tropical storms developed in the Atlantic last year, but only two made landfall in the United States.