Flood-prone Houston hit by heavy rain as Harvey batters coast

(CNN) — Bands of heavy rain from Hurricane Harvey began pummeling Houston early Saturday as the flood-prone city braced for what could be several days of downpours as the monster storm hovers over Texas.

Harvey made landfall as a Category 4 storm late Friday between Port Aransas and Port O’Connor, Texas, about 150 miles southwest of Houston, the nation’s fourth largest city with a metropolitan-area population of 5 million people.

A flash-flood watch was in effect Saturday for the Houston area, according to the National Weather Service, with CNN predicting as much as 22 inches of rain over the next week. By 7 a.m. ET, the city had gotten 1.44 inches of rain over the prior 24 hours, the weather service’s Houston office reported.

And more heavy rain was expected, with Harvey due to stall over southeast Texas. The system could maintain tropical storm strength through early Wednesday, then weaken into a tropical depression, the weather service predicted.

“People need to know this is not a one-, two-day event and done,” Houston Mayor Sylvester Turner said Friday. “Even though it may seem like it will get better, this is a four- or five-day event, starting tomorrow evening, going through Monday or Tuesday.”

“It’s all hands on deck,” Turner said. “The fire department is ready, the police department is ready. The emergency management is 24 hours. We will stay with this thing all the way through.”

Houston residents should “exercise common sense,” and stay off the roads this weekend, the mayor said.

Houston public schools have canceled classes on Monday, which was scheduled to be the first day of the academic year. The city’s parks and main zoo also are closed. The Houston Dynamo, the city’s Major League Soccer team, canceled its Saturday game, and Coldplay canceled a concert Friday night.

Voluntary evacuation orders were in place Saturday for several communities around Trinity Bay in Harris County, which is also home to Houston, county officials said.

Flat land means flood risk

Houston’s main concern from Harvey remained the flood risk, with one estimate setting the potential for damage at $20 billion in metropolitan Houston alone, analytics firm CoreLogic said.

Strong storms last spring claimed at least eight lives and caused at least $5 billion in property damage in Harris County. Damaging flooding from heavy rain also socked Houston in the fall of 2015.

Houston floods easily because of how flat it is, CNN meteorologist Jennifer Varian said.

“They start flooding between 2 and 3 inches” of rain over a short time, Varian said, adding that the amount of rain predicted in Houston from Harvey is “going to be far exceeding that.”

“In the next seven days,” Varian said, “Houston is looking at 22 1/2 inches.”

Many have compared Harvey with Tropical Storm Allison, which in 2001 killed 23 people and caused billions of dollars in damage in Texas, according to the National Hurricane Center. Allison stalled over land and dumped more than 30 inches of rain on Houston, causing catastrophic flooding.

Compared with Harvey, Varian said, “Allison was a measly little storm.”