A swath of East Texas remained under a flash flood watch early Friday as the remnants of Tropical Depression Imelda drifted north after killing at least two people.

Rainfall intensity began to weaken late Thursday, the National Weather Service said, ending a day of about 1,700 combined rescues and evacuations in Harris County alone. 

Some of the county's 4.7 million residents, which includes Houston, might not see waters recede until the weekend, officials said. Authorities planned to work to clear freeways of abandoned vehicles overnight, Houston Police Chief Art Acevedo said.  

In Jefferson County, a 19-year-old man drowned and was electrocuted while trying to move his horse during a lightning storm, Sheriff's Office spokesperson Crystal Holmes said. A man also died after being rescued from a submerged van, Harris County Sheriff Ed Gonzalez tweeted.  

More than 40 inches of rain drenched Jefferson County in the past three days, the National Weather Service office in Houston said, making Imelda the seventh wettest tropical cyclone in U.S. history. 

"This is an incredibly dangerous, life-threatening situation," the office said.

Houston authorities said three people had minor injuries after the flat roof of a post office facility collapsed amid the pounding rains.

Service with a smile: Imelda left Satchel Smith as the lone employee at a Homewood Suites in Texas. He smiled and went to work

George Bush Intercontinental Airport in Houston ordered a full ground stop, then struggled with arrival delays averaging almost four hours, the Federal Aviation Administration reported. Metro Houston shut down public transportation, and Mayor Sylvester Turner announced that "high water assets" were deployed in parts of the city. 

The storms entering Houston drove wind gusts of up to 50 mph, the National Weather Service said. The water-swollen grounds will make trees more susceptible to being knocked over, and flash flooding remained the main concern, the weather service warned.

Imelda drenched the Jefferson County town of Hamshire with more than42.6 inches of rain – including 25 inches of rain in 12 hours – AccuWeather reported. AccuWeather meteorologists predicted localized rain totals could reach an astonishing 55 inches before Imelda's remnants drift away Friday.

"It's bad. Homes that did not flood in Harvey are flooding now," Jefferson County Judge Jeff Branick told the Beaumont Enterprise.

Hurricane Harvey slammed the state in August 2017, a Category 4 beast when it made landfall in Southeast Texas. Parts of Beaumont were devastated by the killer storm.

Two years later, areas of Beaumont found themselves again submerged under more than 20 inches of rain. Jefferson County authorities warned that up to 10 more inches could fall. 

“The water kept rising. It kept rising. I couldn’t believe it,” said Ruby Trahan Robinson, 63, as she settled in a shelter in a town just outside Beaumont. 

Lamar University shut down for the day. Police warned residents not to leave homes or drive on flooded roads. They pleaded for patience, noting some called 911 reporting inconveniences. 

"The 911 operations center has experienced a heavy call load with over 250 high water rescues and 270 evacuation requests," police tweeted. "If there is an immediate threat to life safety, call 911."

A few miles away in Winnie, vehicles were almost completely covered by water. Evacuations took place at Riceland Medical Center, swamped by more than 4 inches of water.

The Chambers County Sheriff's Office deployed high water rescue vehicles and airboats to pluck residents from flooded homes.

"Winnie is being devastated by rising water," Sheriff Brian Hawthorne said. Mo Danishmund, chief financial officer for Riceland Healthcare, told the Houston Chronicle the flooding was "worse than Hurricane Harvey."

Elsewhere, Tropical Storm Jerry strengthened into a hurricane Thursday as it trekked westward toward Puerto Rico along a path already followed this year by Hurricanes Dorian and Humberto. The National Hurricane Center said Jerry's center was expected to pass north of Puerto Rico on Saturday and east-northeast of the southeastern Bahamas on Sunday. 

Hurricane Humberto weakened to a post-tropical cyclone late Thursdayafter lashing Bermuda on Wednesday. 

Contributing: Doug Stanglin and Doyle Rice, USA TODAY; The Associated Press