More than half a dozen airports in and around Houston, including one of the nation’s busiest aviation hubs, remained closed Monday amid catastrophic flooding and unprecedented rainfall associated with Tropical Storm Harvey.

Houston’s major airports — George Bush Intercontinental, the city’s largest, and William P. Hobby Airport — are expected to remain closed until Wednesday, the Federal Aviation Administration said Monday morning in an air traffic report. Later on Monday, United Airlines said George Bush Intercontinental would be closed until at least Thursday. Roads are flooded throughout Houston, and thousands of flights have been canceled. Airlines are offering travel waivers to ticketed passengers, allowing them to reschedule their flights into September.

More than 54 million passengers made their way through the Houston Airport System last year. Most of them came through George Bush Intercontinental, which has flights to more than 70 international destinations and to more destinations in Mexico than any other airport in the United States.

The airport had just over 16 inches of rain on Sunday, doubling the previous record of more than 8 inches set in 1945, according to the National Weather Service forecast office in Houston/Galveston. William P. Hobby Airport serves far fewer people (about 13 million last year), but offers nonstop flights to dozens of destinations in the United States, Mexico, Latin America and the Caribbean, and is one of Southwest Airlines’s most active hubs. The carrier issued a travel advisory asking people not to attempt to reach Hobby Airport.