Much of the Houston metro area remains underwater Tuesday morning after 11 inches of rain fell in the dark of night. Extreme rainfall rates caused bayous to swell far past their banks, stranding drivers on major thoroughfares and prompting a flash flood emergency. The storm followed quick on the heels of a similarly critical flash flood event for the Austin and San Antonio areas Saturday night.
Heavy rain began to spread across the Houston area around 9 p.m. on Monday night. It was the southern flank of a line of storms pushing east across the southern U.S., associated with a deep, upper-level trough combined with extremely moist surface conditions. As the system reached the Houston area, it slowed down as it encountered a very damp air mass, which led to extreme rainfall rates and totals.
By 11 p.m., the National Weather Service in Houston was forced to issue a flash flood emergency for the hardest hit areas of Harris, including the western Houston metro, and Fort Bend counties. A flash flood emergency is only issued in the most life-threatening rainfall situations. The Houston Weather Service office hasn’t needed to issue one since Hurricane Ike in 2008.
The southwest area of Houston received nearly 11 inches of rain overnight, but totals over 6 inches were widespread across the counties of Fort Bend and Harris, which includes the city of Houston.
Overnight rainfall rates of 2 to 3 inches per hour were widespread across the Houston metro area. The National Weather Service reports that around 11 p.m., the 1-hour rainfall rate at one part of the Buffalo Bayou, one of two slow-moving rivers that flow through Houston, was up to 4.16 inches.
The river gauge on the Buffalo Bayou at Shepherd Drive, which is in west Houston, climbed from around 3 feet at 9 p.m. on Monday night, peaking at around 34 feet at 5 a.m. Tuesday morning. This is the sixth highest crest on record for the location. At this point on the Buffalo, major flooding begins at 32 feet, inundating major parkways, and homes upstream of the gauge begin to flood. Weather.com reports that the flooding at the Upper Brays Bayou was near the all-time record flood event of September 1983 at that location.
Interstates are submerged and cars are abandoned on Monday morning after the overnight deluge. The Texas DOT is reporting flooding along nearly every major freeway in the Houston area. Images and video from social media are sobering and similar — parts of Houston were transformed into a lake overnight, dangerously deep at some locations, and city officials are asking residents to just stay home today, if at all possible.
A flash flood watch remains in effect for the Houston region until noon central time Tuesday. A flood warning has been issued for the entire Houston metro area until 2:45 p.m. The National Weather Service continues to use strong language to dissuade drivers from trying to cross flooded roads. Drivers often don’t realize that it may only take less than a foot of moving water to carry a vehicle away — but they also run the risk of stalling out and becoming trapped in potentially rising water, which ends up risking not only their lives but those of the emergency responders who perform water rescues.
Monday night’s torrential rainfall was yet another storm in a very wet pattern for Texas over the past month. According to the National Weather Service, the Houston area has seen up to around 15 inches of rain since May 1, while northern Texas and Oklahoma totals are pushing past 20 inches.
Houston Hobby Airport itself has recorded 10.28 inches of rain so far this month, which makes this the eighth-wettest May on record for the location. The wettest May on record for the airport was in 1970 when 14.84 inches of rain fell. Weather records go back to 1930 at Houston Hobby.