Residents along the US Gulf Coast have been placed on alert as approaching Tropical Storm Karen threatens damaging winds, heavy rain and high tides.
Oil platforms in the Gulf of Mexico have also started shutting production as Tropical Storm Karen sweeps in.
The White House said the Federal Emergency Management Agency (FEMA) was recalling some employees sent home by the US government shutdown.
Karen is forecast to lash the northern Gulf Coast over the weekend.
The storm is grinding slowly north-west and could be at or near hurricane strength by late Friday or early Saturday, forecasters said.
A hurricane watch has been issued for the coast from Grand Isle, Louisiana, east to Indian Pass, Florida,
“Now is the time for people to review their emergency plans in case conditions worsen,” Mississippi Governor Phil Bryant said.
In Louisiana, Governor Bobby Jindal declared a state of emergency while his Florida counterpart Rick Scott also declared an emergency for 18 counties.
Army engineers in Louisiana are also closing a huge barrier intended to keep storm surges out of the Inner Harbor Navigation Canal where levee breaches during Hurricane Katrina in 2005 led to catastrophic flooding.
In Alabama, safety workers raised double red flags along beaches warning of treacherous rip currents.
Off the coast, BHP Billiton said it was fully evacuating and shutting oil and gas production at its two platforms in the Gulf of Mexico.
Anadarko Petroleum Corp said it had done the same at one of its eight platforms.
On Thursday afternoon the National Hurricane Center in Miami said Karen was about 400 miles south of the mouth of the Mississippi River and had maximum sustained winds of 65 mph with higher gusts.
Heavy rain could also affect parts of Cuba and Mexico’s Yucatan Peninsula in the next couple of days, the forecasters said.
The hurricane centre forecasters are exempt from the US government shutdown because their work is deemed vital to protecting life and property.
However, the centre’s parent agency, the National Oceanic and Atmospheric Administration (NOAA), carried a message on its website saying: “Due to the Federal government shutdown, NOAA.gov and most associated web sites are unavailable.”
It referred visitors to the National Weather Service for vital information.
Tropical Storm Karen will become a hurricane if its sustained winds reach 74 mph.
The storm, which formed in the south-eastern Gulf of Mexico on Thursday, is the first to threaten the US coast during the 2013 Atlantic hurricane season.