Tropical Storm Hanna is expected to grow into a hurricane by the time it makes landfall on the southern Texas Gulf coast Saturday afternoon or early evening.
The U.S. National Weather Center says dangerous to catastrophic flash flooding is expected.
Hanna is set to move southwesterly into Deep South Texas by Sunday morning before it crosses the Rio Grande into Mexico.
Rainfall of 15 to 30 centimeters is likely, with as much as 46 centimeters possible, the weather service says.
Hurricane force winds are predicted as Hanna travels across sections of the Texas ranchlands.
Forecasters predict power outages.
To the South and East, Tropical Storm Gonzalo is moving with maximum sustained winds of 65 kilometers per hour, bringing gusty wind and heavy rains to the Southern Windward Islands Saturday.
A Tropical Storm Warning is in effect for St. Vincent and the Grenadines, Tobago, and Grenada and its dependencies.