Tropical Depression Bill drenched large parts of Texas on Wednesday, turning streets into lakes, raising flood worries and killing at least one person in the state where severe weather killed about 30 people last month.
There were scores of traffic accidents related to Bill, the second named tropical storm of the 2015 Atlantic hurricane season. It was downgraded from a tropical storm on Wednesday as it lost power. It first came ashore on Tuesday and has taken a northern path into central Texas.
The heavy rains could cause rivers already swollen from torrential rains in late May to spill over their banks again.
"This event is not over," Texas Governor Greg Abbott said at a news conference. "There will be a lot of rainfall that will still come. There could be some potential tornadoes."
A 62-year-old woman died on Wednesday when she lost control of her car on a rain-soaked highway near the central town of West, a state trooper said.
Rainfall is expected to be 4 to 8 inches (10 to 20 cms) over eastern Texas and eastern Oklahoma and 3 to 6 inches over western Arkansas and southern Missouri. Some areas could see as much as 12 inches (30 cms), the National Hurricane Center said.
"These rains may produce life-threatening flash floods," it said. The heavy rains shut roads and snarled transportation in the Houston and Dallas areas, two of the largest U.S. metropolitan areas.
More than 160 flights were canceled at Dallas and Houston airports, some of the nation's busiest, as of 11 a.m. CDT, tracking service FlightAware.com said.
The National Weather Service issued a flash flood watch for an area from the Texas coast into Illinois, affecting more than 20 million people.
"It's not fun taking your dogs out to pee during a tropical storm," said Dallas resident Christal Neumann. "I had to coax them out the door with an umbrella."
In Sealy, about 50 miles (80 kms) west of Houston, police rescued people caught in rising water.
Voluntary evacuations were called for some flood-prone areas south of Houston.
Oilfields in the Gulf of Mexico and near the coast were not impacted by the storm.
Refineries and a nuclear power plant, the South Texas Nuclear Generating Station in Bay City, also operated normally.
More than 45 percent of U.S. refining capacity and half of natural gas processing capacity sits along the U.S. Gulf Coast.