Floodwaters were rising across swathes of Houston as Tropical Storm Harvey continued to inundate southeastern Texas, pounding America’s fourth-largest city with unprecedented levels of rainfall and crippling the core of the U.S. energy industry.While the metropolis has dealt with some of the nation’s worst deluges, elected officials, meteorologists and emergency managers say it’s never faced anything like the current record floods, which may worsen as the downpour is expected to last for days. “Houston has another 100 hours of this,” said Todd Crawford, chief meteorologist at The Weather Company in Andover, Massachusetts. “Words really can’t express the impacts this will have, when all is said and done. There is no historical comparison. It is simply a tragedy of epic proportions.” After smashing ashore Friday as the strongest storm to hit the U.S. since 2004, rains and flooding from the slowed cyclone became the biggest threat. More than 25 inches of rain has already fallen in some areas and another two feet is possible, the National Hurricane Center said in an set of advisories at about 11 p.m. New York time. For more information on tropical storms such as hurricanes and typhoons, click here. 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 percent of U.S. refining capacity. Crops, livestock and drinking water are also under threat and rail shipments near Houston have been delayed. Airlines had canceled almost 1,847 flights Sunday at airports in Houston, Corpus Christi, San Antonio, Austin and Dallas, and another 1,580 were scrubbed for Monday, according to FlightAware, an airline-tracking service. “It is very bad flooding, rivaling the Katrina disaster in some cases,” Brett Rossio, a meteorologist with AccuWeather Inc. in State College, Pennsylvania, said by telephone, referring to the 2005 disaster centered in neighboring Louisiana. “Some places will get greater than 30 inches; this is very deep, tropical moisture that is lifting northward.” Harvey, which had stalled northwest of Victoria, Texas, started to drift back toward the Gulf of Mexico, the hurricane center said. The worst would be if it re-intensifies Monday into Tuesday before swinging back into the southeastern Texas coast, Rossio said. While the storm may intensify slightly as it moves over water, the hurricane center said it’s not forecasting significant strengthening. At least 19 points across southeastern Texas were expected to set flooding records, said Greg Waller, a service coordination hydrologist with the National Weather Service in Fort Worth, Texas. Buffalo Bayou, a waterway that runs through downtown Houston, broke its old flood record Sunday morning and was forecast to stay above that mark until Wednesday. Major roadways in Houston had flooded by Sunday morning, some under several feet of water, while motorists have been stranded on freeways for hours because off-ramps are inundated. Mayor Sylvester Turner opened the city’s downtown convention center to residents left homeless by the storm, while the city’s police urged residents to stay in their houses if they faced only manageable levels of flooding. “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.” President Donald Trump approved a major disaster declaration, making federal assistance available to supplement state and local 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. The Federal Emergency Management Agency, meanwhile, is prepared to be in the Houston area “for years,” Administrator Brock Long told CNN on Sunday. 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.” Electricity service was cut to about 243,505 customers in Texas as of 9:25 p.m. local time, according to a tally of utility blackout reports by Bloomberg. Severe flooding was hampering the ability of crews to assess damage and restore service in certain areas, the Washington-based Edison Electric Institute said.   Gasoline futures on Monday surged to the highest in two years. 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. The rain is also 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. Ports at the Texas Gulf account for about 24 percent of U.S. wheat exports, as well as 3 percent of corn shipments and 2 percent of soybeans, according to the Soy Transportation Coalition, citing data from the U.S. Department of Agriculture. 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. The region handles about 60 percent of the country’s soybean exports, as do 59 percent of corn shipments, Mike Steenhoek, executive director for the group, said Thursday in an email. Tornadoes are also possible near the upper Texas coast and into far southwest Louisiana, the hurricane center warned. “If you live through this event it is one you will remember for the rest of your life,” Waller said.