Nearly 1 million people along the Texas coast were ordered to evacuate ahead of the storm, which was expected to strike late today or early Saturday. But in a calculated risk aimed at avoiding total gridlock, authorities told most people in the nation’s fourth-largest city to just hunker down.

Ike was steering almost directly for Houston, where gleaming skyscrapers, the nation’s biggest refinery and NASA’s Johnson Space Center lie in areas vulnerable to wind and floodwaters. Forecasters said the storm was likely to come ashore as a Category 3, with winds up to 130 mph.

But the storm was so big, it could inflict a punishing blow even in those areas that do not get a direct hit. Forecasters warned that because of Ike’s size and the state’s shallow coastal waters, it could produce a surge, or wall of water, 20 feet high, and waves of perhaps 50 feet. It could also dump 10 inches or more of rain.

“It’s a big storm,” Texas Gov. Rick Perry said. “I cannot overemphasize the danger that is facing us. It’s going to do some substantial damage. It’s going to knock out power. It’s going to cause massive flooding.”

Hurricane warnings were in effect over a 400-mile stretch of coastline from south of Corpus Christi to Morgan City, La.