The U.S. National Hurricane Center downgraded Harvey to a tropical depression from a tropical storm as it moved through Louisiana on Wednesday.

In the Houston area, floodwaters started dropping and the sun peeked through thinning clouds in the first glimmer of hope in days for the besieged city. But the crisis was far from over, and the storm began to give up some of its dead.

The number of confirmed deaths rose to 31, including six family members — four of them children — whose bodies were pulled Wednesday from a van that had been swept off a Houston bridge into a bayou.

"Unfortunately, it seems that our worst thoughts are being realized," Harris County Sheriff Ed Gonzalez said of the discovery.

Late Wednesday, the Harris County coroner's office confirmed six more flood-related deaths including a man who stepped on live electrical wire in floodwaters and an evacuee who was found unresponsive on a charter bus. Most of the other deaths were drownings.

Autopsies will be performed on eight other people to see if their deaths were storm related.  

While conditions in the nation's fourth-largest city appeared to improve, another crisis related to Harvey emerged at a chemical plant about 40 kilometres northeast of Houston. A spokeswoman for the Arkema Inc. plant in Crosby, Texas, said late Wednesday that the flooded facility had lost power and backup generators, leaving it without refrigeration for chemicals that become volatile in higher temperatures.

"The fire will happen. It will resemble a gasoline fire. It will be explosive and intense in nature," said Janet Hill, spokeswoman for the French company.

The last of the plant's employees evacuated on Tuesday and residents within 2.4 kilometres were told to leave, Hill said, though the timing of the explosion remains unclear. 

Another threat was east of Houston where conditions deteriorated close to the Louisiana line as Harvey again reached land.

The Texas communities of Beaumont and Port Arthur struggled with rising floodwaters and worked to evacuate residents after Harvey rolled ashore early Wednesday for the second time in six days, hitting southwestern Louisiana as a tropical storm with winds of 72 km/h and heavy rain.

Forecasters downgraded Harvey to a tropical depression late Wednesday from a tropical storm but it still has lots of rain and potential damage to spread, with 10 to 20 centimetres forecast from the Louisiana-Texas line into Tennessee and Kentucky through Friday. Some spots may get as much as a foot, raising the risk of more flooding.

Tropical storm Harvey rumbles into Louisiana and Mississippi0:50

For the Houston and Galveston areas, the NHC says the threat of heavy rains has ended and the water is already back within its channels in some places. Houston Mayor Sylvester Turner said the city's two major airports would reopen late in the afternoon.

"We have good news," said Jeff Lindner, a meteorologist with the Harris County Flood Control District. "The water levels are going down. And that's for the first time in several days."

Thousands of homes still swamped

Nevertheless, many thousands of homes in and around the nation's fourth-largest city were still swamped by the record-breaking deluge of 132 centimetres of rain, and could stay that way for days or weeks. And officials said 911 call centres in the Houston area were still getting more than 1,000 calls an hour from people seeking help.

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A woman is overcome with grief after being rescued from her home flooded by tropical storm Harvey in Orange, Texas, U.S., Aug. 30. (Jonathan Bachman/Reuters)

The scale of the catastrophe in Texas began to come into sharper focus: Emergency authorities said more than 1,000 homes were destroyed and close to 50,000 damaged, and over 32,000 people were in shelters across the state.

Authorities expect the death toll to rise as the waters recede and bodies are found in cars and homes. Harris County officials said they are investigating 17 deaths to determine whether they were storm-related.

The confirmed deaths from the storm include a man who tried to swim across a flooded roadway, a former football and track coach in suburban Houston and a woman who died after she and her young daughter were swept into a rain-swollen drainage canal in Beaumont. The child was rescued clinging to her dead mother, authorities said.

Seeking financial help

Texas Gov. Greg Abbott said there were 32,000 people in shelters and that 210,000 people have registered for Federal Emergency Management Agency (FEMA) assistance. He said FEMA has approved $37 million in financial assistance for individuals.

Those numbers expected to climb dramatically in the coming days and weeks, the FEMA chief said.

GFX Harvey August 30

"This is going to be an incredibly large disaster," Brock Long said in Washington. "We're not going to know the true cost for years to come.... But it's going to be huge."

Harvey 'spinning down'

Harvey itself was "spinning down" and expected to weaken sometime Wednesday into a tropical depression, meaning winds of 61 km/h or less, U.S. National Hurricane Center meteorologist Dennis Feltgen said.

Forecasters said the remnants of the hurricane will move from Louisiana into Mississippi, Tennessee and Kentucky in the next few days, with flooding possible in those states.

"Once we get this thing inland during the day, it's the end of the beginning," Feltgen said. "Texas is going to get a chance to finally dry out as this system pulls out."

Eugene Rideaux, a 42-year-old mechanic who showed up at evangelist Joel Osteen's Houston megachurch to sort donations for evacuees, welcomed the reprieve from the rain.

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Floodwaters surround a power sub-station in Iowa, Calcasieu Parish, in Louisiana on Tuesday night. Foreboding images of Harvey lit up weather radar screens on the 12th anniversary of the day Hurricane Katrina made landfall in Louisiana. (Jonathan Bachman/Reuters)

He said he had not been able to work or do much since the storm hit, so he was eager to get out of his dark house and help.

"It's been so dark for days now, I'm just ready to see some light. Some sunshine. I'm tired of the darkness," Rideaux said. "But it's a tough city, and we're going to make this into a positive and come together."

Harvey's return

When Harvey paid its return visit to land overnight, it hit near Cameron, La., about 72 kilometres from Port Arthur.

Port Arthur found itself increasingly isolated as floodwaters swamped most major roads out of the city and spilled into a storm shelter with about 100 people inside. Motiva Enterprises closed its Port Arthur refinery, the largest in the nation, because of flooding.

Port Arthur Mayor Derrick Freeman posted on his Facebook page: "city is underwater right now but we are coming!" He urged residents to move to higher ground and avoid getting trapped in attics.

Harvey initially came ashore as a Category 4 hurricane in Texas on Friday, then made a U-turn and lingered off the coast as a tropical storm for days, inundating flood-prone Houston.

Harvey's five straight days of rain totalled close to 132 centimetres, the heaviest tropical downpour ever recorded in the continental United States.

With files from CBC News