Tropical Storm Edouard hit the upper Texas coast today, bringing driving rains and winds near 100 kilometres per hour.
Edouard, the fifth tropical storm of the 2008 Atlantic hurricane season, was just shy of hurricane strength when it came ashore halfway between High Island and Sabine Pass, forecasters said.
The storm will weaken as it moves inland, the US National Hurricane Centre said. The storm's sustained winds fell just short of hurricane speeds of 119 km/h.
The storm formed near a major oil- and gas-producing area of the northern Gulf of Mexico on Sunday and had previously been forecast to come ashore farther south, near Galveston.
A storm surge of 0.6 to 1.2 metres was expected for coastal areas between Grand Isle, Louisiana, and Sargent, Texas, the Miami-based centre said.
Flooding was the primary concern. The storm could cause rain accumulation up to 13 cm in coastal regions of Louisiana and up to 25 cm in some parts of southeastern Texas, US forecasters said, adding that isolated tornadoes were also possible.
Texas Gov. Rick Perry on Monday declared 17 counties disaster areas and mobilised about 1,200 National Guard troops.
A statewide emergency was declared in Louisiana.
The storm shut down a huge offshore oil port, closed the Houston Ship Channel and prompted several offshore operators to evacuate staff from their platforms.
A series of powerful hurricanes in 2004 and 2005, including Hurricane Katrina, toppled oil rigs and severed pipelines in the gulf.
The six-month hurricane season, which began on June 1st, has already seen two of this year's storms strengthen into hurricanes. Last month was the third most active July for storms since records began in 1851.