Slow-moving summer storms capable of extreme rain are poised to drench the East Coast Monday, threatening millions from North Carolina to New England with even more dangerous flash flooding.

Over 130 people have died after heavy rain pounded Kerr County, Texas, early Friday, leading to "catastrophic" flooding, the sheriff said.

The National Weather Service warned that the Guadalupe River could surge to nearly 15 feet—5 feet above flood stage—by Sunday afternoon.