Houston: The tropical weather season revved up as the Atlantic's first hurricane formed and quickly strengthened, and as Tropical Storm Erin's remnants soaked rain-weary Texas, snarling rush-hour traffic and killing at least two people.

Even as they fetched dozens of stranded drivers on Thursday, authorities in Houston and San Antonio looked over their shoulders at Hurricane Dean, a Category 2 storm building in the Atlantic as it neared islands in the eastern Caribbean.

Hurricane warnings were issued for some islands, and a tropical storm warning was issued for the US Virgin Islands and Puerto Rico.

The thunderstorms from Erin brought 18 centimetres of rain to parts of San Antonio and Houston, where one person died and another was injured when the waterlogged roof of a storage unit outside a grocery store collapsed, Fire Chief Omero Longoria said.

The National Hurricane Centre said 25 centimetres of rain was possible in some areas.

In San Antonio, a man was swept away after apparently getting out of his vehicle in floodwater, a police spokeswoman said. Three people died in a head-on collision on a rain-soaked highway in Comal County.