Tropical Storm Isaac gathered strength early Tuesday and was on the verge of becoming a Category 1 hurricane as it rumbled toward the Gulf Coast, though precisely where it will make landfall remains guesswork, forecasters said Tuesday.
Isaac is projected to land somewhere along the Mississippi or Southeast Louisiana coast on Tuesday evening, possibly as an even stronger Category 2 hurricane, according to the National Weather Service.
Even before then, a wide swath of coastal area - and extending inland from Louisiana to the Florida panhandle - is likely to buffeted by strong winds, rain of as much as 15 inches and flooding. The threat of tornadoes will also increase as the storm approaches.
Isaac has been fickle and confounded predictions all along.
The most serious danger may not be from the 100-mile-per-hour winds, but by the enormous amount of water that the storm will be bringing with it and pushing in front of it. Officials encouraged those in low-lying areas to leave, warning of 12-foot storm surges along a broad swath of the coast and days of nonstop rainfall, in some places possibly adding up to 20 inches of water.
"A slow-moving, large system poses a lot of problems," Rick Knapp, the director of the National Hurricane Center, said in a conference call with reporters, describing the risks as "life-threatening, potentially."
Any discussion among Louisiana residents about whether to stay or go was running out of time. Tropical-storm-force winds were expected to arrive overnight, rendering a last-minute escape more dangerous than sticking around. Gov. Bobby Jindal urged people in low-lying areas and places outside of levee protection to leave for safer ground, but in any case to make up their minds quickly.
"Today is the day, for those that want to leave, today is the day they should move," Mr. Jindal said at a news briefing, surrounded by the presidents of several coastal parishes.
A mandatory evacuation of New Orleans is triggered by a Category 3 hurricane, a status Isaac is unlikely to reach. But the time frame for a safe and effective citywide evacuation expired on Monday anyway.
So those who remain here, as most have, will be marking the seventh anniversary of Hurricane Katrina on Wednesday not with ribbon cuttings and modest ceremonies as planned, but by hunkering down under heavy rains and winds.
All storms have their own personalities, and Isaac promises a very different experience from Katrina. While it could possibly hit New Orleans directly - unlike Katrina, which landed in Mississippi but sent surge waters against the city's faulty levees and flood walls - Isaac will have to contend with a $14.5 billion flood protection system that has been all but completed by the Army Corps of Engineers.
This system, along with its profile and a rapport between parish, state and federal authorities that is far stronger than the dysfunctional relationship that characterized the response effort to Hurricane Katrina, bolstered the confident statements made by city officials on New Orleans's ability to bear up.
"We know now, based on the latest information, which is always subject to change, that we are going to have a hurricane that is going to hit New Orleans," Mayor Mitchell J. Landrieu said at a news briefing on Monday. But, he added, "there's nothing this storm will bring us that we are not capable of handling."
After a tremor of anxiety on Saturday night and Sunday, when it became clear that Isaac had turned its gaze to Louisiana, the sort of autopilot pragmatism that comes from living in hurricane country kicked in. By Sunday night, New Orleans residents had stripped bare the shelves of some grocery stores and sucked some gas stations dry.
The decision to stay for most people was perhaps in part due to reports on Monday morning that Isaac had yet to - in the disparaging phrase of several meteorologists - "get its act together," and was projected to make landfall as a Category 1 hurricane or possibly even a strong tropical storm. But that forecast turned worse by the afternoon, and in any case officials urged residents all along the Gulf Coast not to focus on the projected intensity, or even the location of landfall. A huge, wet and sluggish storm like Isaac could wreak havoc far and wide, regardless of its strength, they said, just as Tropical Storm Lee last year did with flooding as far north as Pennsylvania and New York.
The storm has already forced the evacuation of workers from 346 oil and gas platforms in the Gulf of Mexico, which are responsible for 17 percent of domestic oil production and 6 percent of natural gas production, though it has so far had little effect on the price of commodities. It has also led to at least one confirmed tornado, in Vero Beach, Fla., and has put officials far beyond the shore on alert for more.
"We're still recovering, so we are geared up as much as any staff members can be," said Yasamie August, information manager for the Alabama Emergency Management Agency, in a state that was devastated by tornadoes last year.
Mandatory evacuations have been announced in low-lying areas in Alabama and Mississippi, and shelters have opened all along the coast. The evacuations were also announced in several communities outside the levees in south Louisiana, as well as for the entire parish of St. Charles, west of New Orleans.
Renee Simpson, a spokeswoman for the parish, said the evacuation was called for because much of the parish is unprotected by levees from the surging gulf. She pointed out that a mandatory evacuation did not mean people would be arrested or roads closed, but amounted to a warning that, with electrical failures and extensive flooding likely, people who chose to say would essentially be on their own.
This did not seem to bother many St. Charles residents, who seemed mildly amused that people would leave for anything under a Category 3.
"Category 1 or 2, I'm staying; strong 3, 4 or 5, yeah, I'm out," said Dale Daunie, a teacher in Luling. "We're just going to grin and bear it for a little bit. You know, barbecue and make the best out of it."
Anjanette Joseph, a nurse in Destrehan, concurred with that analysis, judging the risks not worth the inconveniences of a hasty exit. "All the hotels were booked up for pets, and we have a dog and a mouse, so we decided to stay," she said.
This attitude concerned Louisiana officials, who warned that multiple days of rain on top of dangerous storm surges would severely test local drainage systems and that days without power in a Louisiana summer is not something anyone would want. But the gulf mentality dies hard.
"I'm not afraid of the storm," said Denise Maul, a retired nurse who has an apartment in New Orleans with her husband. Her car was loaded, and she was planning to leave on Monday afternoon, she said. But they are only going to Mobile, where they have a house. It was a matter of comfort, not security. "My dad used to always say, 'Rainy weather ain't good for nothing but ducks and lovers,' " she said.
© 2012, The New York Times News Service