(Bloomberg) – Unprecedented flooding from Tropical Storm Harvey was inundating Houston and the surrounding area as bands of torrential rain pinwheeled across South Texas, the heart of U.S. energy production.

Cat 4 winds & rain

Harvey smashed ashore near Rockport, Texas Friday as a Category 4 hurricane. As the winds subsided Sunday to about 40 miles per hour, from 130 miles per hour earlier, rain and flooding took over as the main threat from a storm that's the strongest to hit the U.S. since 2004.

As much as 25 inches of rain has already fallen and another two feet is possible, the National Hurricane Center said at 5 p.m. New York time.

At least 2 deaths

Two deaths are attributed to the storm, which has also halted about one quarter of oil and natural gas production in the Gulf of Mexico and more than 10% of U.S. refining capacity. In addition to energy, crops, livestock and drinking water are under threat. In addition to energy, crops, livestock and drinking water are under threat. Airlines have canceled almost 3,000 flights at multiple Texas airports.

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“It is very bad flooding, rivaling the Katrina disaster in some cases,” said Brett Rossio, a meteorologist with AccuWeather Inc. in State College, Pennsylvania, by telephone. “Some places will get greater than 30 inches; this is very deep, tropical moisture that is lifting northward.”

BNSF Railway Co. said Sunday that heavy rain and unprecedented flooding is causing “significant service disruptions” in the Houston area and throughout southeastern Texas.

Intermittent amounts of water will be released from the Addicks and Barker reservoirs because of the severe flooding in Houston, the U.S. Army Corps of Engineers Galveston District said in a statement. The dams are designed to protect Houston and the Houston Ship Channel from deluges.

Fears storm may re-intensify

Harvey, which had been sitting northwest of Victoria, Texas, has begun to slowly drift toward the Gulf of Mexico, the hurricane center said. The worst that could happen is it re-intensifies Monday into Tuesday, before once again swinging back into the southeastern Texas coast lands, Rossio said.

“The thing that is even worse when you have this much water is you get contamination of the clean water,” he said. “A lot of places are going to lose their drinking water.”

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Across southeastern Texas, 51 river gauges were showing major flooding, and 41 had reached moderate to minor status, according to the West Gulf River Forecast Center in Fort Worth, Texas. White Oak Bayou in Houston rose almost 30 feet in 24 hours.

Wilford Martinez, right, waits to be rescued by Harris County Sheriff's Department Richard Wagner after his car got stuck in floodwaters from Tropical Storm Harvey on Sunday, Aug. 27, 2017, in Houston, Texas. (AP Photo/David J. Phillip)

Houston roadways flooded

Every major roadway in Houston was flooded by Sunday morning, some with more than 15 feet of water. Motorists have been stranded on freeways for hours because off-ramps are inundated. The city's CBS television affiliate was knocked off the air by floodwaters Sunday, according to tweets by station personnel, and Houston Mayor Sylvester Turner opened the city's downtown convention center to residents left homeless by the storm.

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“This is catastrophic,” said Greg Waller, a service coordination hydrologist with the National Weather Service's West Gulf River Forecast Center in Fort Worth. “When we say record setting it means you cannot use history on your side because the rivers have never been this high before.”

“The word we're using is catastrophic,” Waller said. 'We are trying to discourage people from comparing this to past events. Don't rely on past events. If you think you know what the river will do, you don't because the river has never done this.”

President Donald Trump approved a major disaster declaration, making federal assistance available to supplement state and local recovery efforts. The U.S. Environmental Protection Agency waived certain fuel requirements for gasoline and diesel supplies in Texas, including the Dallas-Fort Worth area, to allay concerns of fuel shortages.

Waters rush from a large sinkhole on Highway FM 762 in Rosenberg, Texas, near Houston, Sunday, Aug. 27, 2017. Police say the sinkhole has opened on the Texas highway as Tropical Storm Harvey dumps more rain on the region. (AP Photo/John Mone)

FEMA prepared to be in Houston 'for years'

The Federal Emergency Management Agency, meanwhile, is prepared to be in the Houston area “for years” as the fourth largest U.S. city takes the brunt of rainfall and flooding from Harvey, Administrator Brock Long said on CNN's “State of the Union” program on Sunday.

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Damage from the initial strike won't tell the whole story, said Chuck Watson, director of research and development, at Enki Holdings LLC in Savannah, Georgia. “If it was a traditional hurricane it would be a $2 billion storm, maybe $3 billion, but that is not what this storm is about,” Watson said.

Agriculture havoc

The rain is wreaking havoc on the largest U.S. cotton producer, hitting Texas at a time when many farmers are storing excess supplies on fields following a bumper harvest.

At least 100 cotton storage modules — capable of holding 13 to 15 bales — blew away near the coastal community of Gregory, Texas, said Jeff McKamey, a farmer who owns a cotton gin that suffered minor damage when part of the piping and roof blew away.

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“We've had the most cotton ever in storage% of U.S. wheat exports, 3% of corn shipments and 2% of soybeans, according to the Soy Transportation Coalition, citing data from the U.S. Department of Agriculture.

Shipping threats

The threat to shipments of corn and soybeans, the top U.S. crops, comes from Harvey's potential impact in Louisiana and the Gulf of Mexico. About 60% of American soybean exports depart from the region, as do 59% of corn shipments, Mike Steenhoek, executive director for the group, said Thursday in an email.

“Heavy rain will delay the ability to load ocean vessels and unload barges,” Steenhoek said in an email. “Heavy winds and storm surges, if they occur, could damage the export terminals.”

Houston Police SWAT officer Daryl Hudeck carries Catherine Pham and her 13-month-old son Aiden after rescuing them from their home surrounded by floodwaters from Tropical Storm Harvey, Sunday, Aug. 27, 2017, in Houston.

Yet to reach some hard hit areas

Harvey was downgraded to a tropical storm after making landfall overnight on Friday night. The death toll, though, is expected to rise as emergency crews were yet to reach some of the hardest-hit areas, the Associated Press reported. On Sunday, Houston police were advising residents to stay in their houses, even if there was some flooding there.

“Non-life threatening water inside home is safer than going outside,” the Harris County Sheriff's Office tweeted on Sunday morning. “Difficult & scary, but we'll get to you. Pls shelter in place. Be Safe.”

Oil & natural gas production shut down

Harvey is flooding a region that has a cluster of refineries that process 5 million barrels of oil a day. About 1 million barrels a day of crude and condensate refining capacity in Texas have been shut by companies including Valero Energy Corp., according to company statements, government releases and people familiar with the situation.

As of Saturday, 24% of oil production and 25.9% of natural gas production in the Gulf of Mexico were shut down, according to the Department of Energy. FlightAware, a Houston-based airline tracking company, reported that almost 2,800 flights to and from Texas airports were canceled Sunday with the majority of those going through Houston.

A coin laundry lost its roof and portions of walls in the wake of Hurricane Harvey, Saturday, Aug. 26, 2017, in Rockport, Texas. (AP Photo/Eric Gay)

300,000+ customers without power

At the same time, more than 300,000 customers remain without power, the Electric Reliability Council of Texas reported. The drop in electricity demand could depress natural gas prices.

Harvey's position is allowing it to pull moisture-laden air off the Gulf, called a feeder band, which will help keep it alive and promises more moisture for Houston, said Dan Pydynowski, a meteorologist with AccuWeather Inc. in State College, Pennsylvania.

“That feeder band is going to remain in the general vicinity of Houston perhaps through Monday or even beyond,” Pydynowski said. “This is going to flood areas that don't typically flood. It is going to have a tremendous impact on businesses, homes, property and the ability to travel in the entire Houston area.”

Tornado threat

Along with the rain, the coast land could face tornadoes, the hurricane center reported in an advisory. Rainfall totals near 20 inches were reported in the Houston area by early Sunday, the hurricane center said.

Related: 5 keys to preparing for tornadoes

If the storm does significant damage to the refineries in the region, the effects could ripple to other parts of the country that rely heavily on the Gulf Coast for fuel supplies. Gasoline futures settled at a three-week high Friday as the storm approached.

“If you live through this event it is one you will remember for the rest of your life,” Waller said.

Continue reading for more photos of property damage caused by Hurricane Harvey:

The basketball facility at Rockport High School lost part of its root and walls in the wake of Hurricane Harvey, Saturday, Aug. 26, 2017, in Rockport, Texas. (AP Photo/Eric Gay)

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A driver works his way through a maze of fallen utility poles damaged in the wake of Hurricane Harvey, Saturday, Aug. 26, 2017, in Taft, Texas. (AP Photo/Eric Gay)

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An official climbs through a window as he checks home damaged by Hurricane Harvey, Sunday, Aug. 27, 2017, in Rockport, Texas. (AP Photo/Eric Gay)

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Flood water surround homes damaged by Hurricane Harvey, Saturday, Aug. 26, 2017, in Rockport, Texas. (AP Photo/Eric Gay)

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People walk past a boat storage facility that was damaged by Hurricane Harvey, Saturday, Aug. 26, 2017, in Rockport, Texas. (AP Photo/Eric Gay)

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A damaged roof is shown after a tornado from Hurricane Harvey, Saturday, Aug. 26, 2017, in Missouri City, Texas. (AP Photo/David J. Phillip)

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Children walk near downed power lines and fallen trees left in the aftermath of Hurricane Harvey, Saturday, Aug. 26, 2017, in Victoria, Texas. (AP Photo/Charlie Riedel)

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Evacuees wade down a flooded section of Interstate 610 as floodwaters from Tropical Storm Harvey rise, Sunday, Aug. 27, 2017, in Houston. The remnants of Hurricane Harvey sent devastating floods pouring into Houston Sunday as rising water chased thousands of people to rooftops or higher ground. (AP Photo/David J. Phillip)

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