The National Weather Service issued a dire warning on Sunday as massive floods inundated Houston in the aftermath of Hurricane Harvey, saying the severe weather conditions were “beyond anything experienced.”

“This event is unprecedented & all impacts are unknown & beyond anything experienced. Follow orders from officials to ensure safety. #Harvey,” it said on Twitter.

It said some parts of Houston and just west of the city may receive a Texas record of 50 inches of rain as Tropical Storm Harvey stalls over Texas.

So far rainfall totals since Thursday evening have reached about 25 inches in south Houston.