Because of its great size, storm surge and gigantic waves are the biggest risk, said Hugh Willoughby, former director of the federal government's hurricane research division. The larger the storm, the longer it hits and the higher the waves can build.
And because the water is so shallow along the Texas coast, the waves pile up, creating a big storm surge, he said.
The port of Houston - the nation's second-busiest - planned to shut down cargo operations until at least Monday. Operators were told to prepare to move their vessels from port.
The storm threatened offshore platforms, land-based refineries and vast chemical complexes along the coast. Dow Chemical Co. planned to shut down its huge operations in Freeport, where the company's plants produce 27 billion pounds of chemicals and chemical products per year.
The Houston Astros said their baseball games today and tomorrow night in Houston would be rescheduled. George Bush International Airport in Houston said all flights would cease after 2 p.m. today.
The airport was jammed yesterday. Angela Redman, 28, begged an American Airlines employee for a seat on a plane headed out of town.
"Please just tell me when I can get on a plane - any plane," Redman said. Accompanied by two toddlers, she was trying to meet her husband in Dallas.
The employee smiled sympathetically and handed her a voucher for a free meal - but no airline ticket.
The Associated Press contributed to this article.
Gasoline: Prices at the pump could pass $4 a gallon as refineries are forced to shut down. PG 8
Ravens: The game is rescheduled from Sunday to Monday in Houston. Sports
Get storm updates on Frank Roylance's blog at baltimoresun.com/weatherblog