(HOUSTON) — At least four people have died Thursday after an “exceptionally” strong storm hit Texas, according to Houston Mayor John Whitmire.

Preliminary investigations indicate falling trees caused two deaths and a fallen crane caused one, according to Houston Police Chief Samuel Pena.

Urging Houston, Texas, residents to stay home, Whitmire said the city was in “recovery mode” and schools will be closed in the Houston area on Friday.

A rare “high risk” warning for flash flooding was issued in Texas and Louisiana early Thursday as the states braced for up to 9 inches of rain in 24 hours.

“The high risk area has seen over 600% of their normal rainfall for the past two weeks alone,” the National Oceanic and Atmospheric Administration warned, and the flash flooding could be life-threatening.

“High risk” days account for just 4% of days, but they are responsible for more than one-third of flooding deaths, according to the Weather Prediction Center.

Rainfall rates could top 2 inches per hour.

The storm first hit Texas on Thursday afternoon, bringing the heaviest rain from Dallas to Waco. Damaging winds, large hail and a few tornadoes are also possible.

The worst flash flooding will be overnight, targeting eastern Texas and western Louisiana.

On Friday morning, the line of storms will continue to push east, bringing a threat of flooding to Louisiana, southern Mississippi and Alabama.

By Friday afternoon and evening, another round of severe storms will develop from New Orleans to Birmingham.

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