When Hurricane Harvey slammed into Texas on Friday, it came with dire warnings about rainfall and the potential for severe flooding.

But it's likely that most residents of the second most populous state never anticipated an amount of water that has shattered records.

In the first graphic, the red dots show areas of major flooding. In the three locations highlighted here, the numbers reflect the water level of the rivers.

At the Buffalo Bayou, for example, a river height of 9.7 metres is considered a major flood. But the river crested Monday at 11.8 metres.

And it's not over yet: the forecast calls for an additional 15 to 31 centimetres of rain through to Friday.

On Tuesday, the National Oceanic and Atmospheric Administration (NOAA) said in a public advisory, "Catastrophic and life-threatening flooding continues in southeastern Texas and portions of southwestern Louisiana."

Here's how the rainfall from the Harvey system compares to that from Hurricane Rita, which was the last major hurricane in the area.

"Isolated storm totals may reach 50 inches (127 centimetres) over the upper Texas coast, including the Houston/Galveston metropolitan area," NOAA warned.

The graphic below shows Harvey's path and strength. It made landfall as a Category 4 hurricane Friday, where it lingered as a tropical storm before moving briefly offshore.

The system is expected to move inland again and continue northeast as a tropical depression.

The National Weather Service office in Houston tweeted about the record-breaking rainfall Tuesday.

As for the human toll, more than 17,000 people have sought refuge in Texas shelters — a number that is only expected to grow. Officials have also warned that the death toll — sitting at more than a dozen, according to some estimates — will likely also rise once floodwaters recede.

"We know in these kinds of events that, sadly, the death toll goes up historically," Acevedo told The Associated Press. "I'm really worried about how many bodies we're going to find."