Floodwaters deepened across much of Texas as storms dumped almost another foot (30 centimetres) of rain on the Houston area, stranding hundreds of motorists and inundating the famously congested highways that serve the fourth-largest US city.
Meanwhile, the search went on for about a dozen people who were still missing, including a group that disappeared after a vacation home was swept down the river and slammed into a bridge.
Several more fatalities were reported four in Houston and four more in Central Texas. That brought to 17 the number of people killed by the holiday weekend storms in Texas and Oklahoma.
Similar search efforts unfolded just south of the Texas-Mexico border, where crews tried to track down the missing and assess the damage in the city of Ciudad Acuna after a tornado killed 13 people Monday.
In Houston, the water rose sharply overnight as about 11 more inches (28 more centimetres) of rain fell, much of it in a six-hour period. By yesterday evening, most rivers had receded back within their banks.
The floodwaters affected virtually every part of the city and paralyzed some areas. Firefighters carried out more than 500 water rescues, most involving stranded motorists. At least 2,500 vehicles were abandoned by drivers seeking higher ground, officials said.
"Given the magnitude and how quickly it happened, in such a short period of time, I've never seen this before," said Rick Flanagan, Houston's emergency management coordinator. The drenching weather threatened to linger. National Weather Service forecasts called for a 20 to 40 percent chance of thunderstorms through the rest of the week in Houston.
The flooding closed several highways, and the ones that stayed open became a gridlocked mess.
Interstate 45 near downtown was backed up for miles on Tuesday morning, and a handful of motorists travelled the wrong way on the highway to retreat from high water.
The small cars weaved between massive 18-wheelers as other drivers stared at them in disbelief. With no end to the backup in sight, some drivers got off the freeway, only to be held up again by water covering nearby access roads.
Some motorists were stuck on I-45 all night, sleeping in their cars until the backup was cleared about 8 am.
NBA fans at the Toyota Center, where the Houston Rockets hosted a Western Conference finals game against Golden State on Monday, were asked with about two minutes left in the game not to leave the arena because of the severe weather.
