Tropical storm Nicholas has been downgraded from a hurricane after making landfall on the Texas coast in the US, bringing heavy rain and the risk of life-threatening flooding.
The storm was upgraded to a hurricane after reaching land at 00:30 (05:30 GMT), but has now weakened.
More than 500,000 power outages have been reported in Texas, according to PowerOutage.us.
President Joe Biden declared an emergency in Louisiana.
It comes just weeks after Hurricane Ida - the fifth strongest to ever hit the US mainland - killed dozens and left more than a million Louisiana residents without power.
Nicholas is carrying maximum sustained winds of 70mph (110km/h), weather officials said, and is expected to hit the Texas coast and upper Louisiana with five to 10 inches of rain.
There could be rainfall of up to 20 inches across central to southern Louisiana, they said.
The US National Hurricane Centre said that Nicholas "has continued to move slowly inland and has weakened during the past few hours".
But it warned that "life-threatening flash flooding impacts, especially in highly urbanised metropolitan areas, are possible", and the National Weather Service called it a "life-threatening situation".
"We want to make sure that no one is caught off guard by this storm," Louisiana Governor John Bel Edwards told a news conference.
He warned that drainage systems still clogged from Ida could trigger flash floods.
More than 119,000 homes and businesses remain without power in Louisiana due to Ida, he added.
Texas Governor Greg Abbott declared states of emergency in 17 counties and three cities.
Houston Mayor Sylvester Turner warned of flooding and urged the city's roughly 2.3 million residents to stay off streets and motorways.
"Take things seriously and prepare," Mr Turner said at a news conference. "This is primarily a rain event and we don't know how much rain we will be getting."
Dozens of schools across the two states have been closed, and hundreds of flights have been cancelled or delayed at airports in the Texas cities of Corpus Christi and Houston.