In addition to winds that have reached 110 miles per hour, Harvey is expected to dump a foot or two of rain on much of Texas.
The projected rainfall is going to be so heavy, in fact, that the National Weather Service had to add an extra colour to its scale to mark the areas expected to get 20+ inches of rain, the Washington Post reports.
The middle and upper part of the Texas coast could get as much as 35 inches of rain — almost 3 feet — according to forecasts as of 11 a.m. Eastern time on Friday.
That rain could create major damage in Texas and Louisiana.
Jeff Masters, a meteorologist at The Weather Company and the co-founder of Weather Underground, told Business Insider that the damage could total as high as $US10 billion, placing it among the most costliest storms in US history. The rain could break records.
“There is an unusual amount of moisture available to this storm, and it is large and powerful, so rainfall records could topple,” he said.