Hurricane Rita has the potential to flood an area almost twice the size of New Orleans when it reaches shore early Saturday, causing tens of billions of dollars in damage to the Houston metropolitan area and plunging yet another major Gulf Coast metropolis into disarray.
A study performed last year by the engineering firm Dodson & Associates found that a Category 5 storm could inundate 369 square miles of Harris County, which contains Houston and some of its suburbs. The study estimated the total cost of a worst-case storm at $80 billion, with 75 percent a result of flooding and the rest from wind damage.
"You're looking at the southeast quadrant of the city of Houston, from downtown to Galveston Bay, being underwater," said Chris Johnson, the president of Dodson & Associates.
That area is home to about 700,000 people, 15 percent of the metro population. It includes the Johnson Space Center, which sits about 20 miles southeast of downtown Houston in a low-lying area threaded by bayous.
NASA evacuated the space center Wednesday, shifting ground control over the International Space Station to a Russian space agency facility outside Moscow.
Also subject to flooding are Texas City and other centers of chemical production and petroleum refining.
As they did before Hurricane Katrina, environmentalists worry Rita could cause the release of toxic pollutants at one or more of the 87 chemical plants, oil refineries or petroleum storage facilities along the Texas coast.
"Dozens of chemical plants and petroleum facilities lie in Hurricane Rita's path, many of which may not be adequately prepared to prevent toxic releases," said Tom Natan, the research director of the National Environmental Trust.
In Galveston, Texas, where the deadliest hurricane in U.S. history killed up to 8,000 people in 1900, flooding is inevitable.
"Galveston is going to suffer," city manager Steven LeBlanc said at a news conference Thursday.
The city is protected by a 16-foot seawall specifically designed to block incoming storm surges. But some forecasters said Rita could pound the barrier with waves twice that high.
As of 1 p.m. Thursday, the National Hurricane Center was predicting Rita would hit land to the east of the Houston-Galveston area, doing its most serious damage around Port Arthur, Texas, on the Louisiana border.
The hurricane was expected to weaken somewhat before reaching shore, but forecasters said it would remain at least a Category 3 storm until then.
In a Category 3 hurricane, flooding around Houston would be limited to about half the area affected by a Category 5 storm.
Wind damage would also be less extensive as well, but it still could easily affect hundreds of thousands of homes.
Whenever a major hurricane makes landfall, the stretch of coast just east of the storm's center is subject to the greatest surge of water, as the counter-clockwise rotation of the cyclone combines with its forward motion to drive water ashore. That makes a landfall around Freeport, Texas, about 40 miles southwest of Galveston, most threatening for the Houston area.
It remains possible that Rita could come ashore that far down the Texas coast, but as of Thursday afternoon the storm appeared more likely to focus its attack closer to the Texas-Louisiana line.
"The forecast right now is something just slightly better than what we dreamed up for worst-case," Mr. Johnson said Thursday morning.