Weather Nerd

Models shift right; threat to N.O. levees

In a potentially ominous sign, the 2:00 PM EDT “spaghetti” computer model map shows some of the computer models shifting Hurricane Gustav’s expected track eastward again (compared to the 8am map), into southeastern Louisiana. The important GFDL model, however, continues to aim toward the west-central part of the state. It’ll be interesting to see what the NHC says about all this in the 5pm EDT advisory.

Meanwhile, even on the current forecast track, which shows Gustav making landfall in the central part of Louisiana, the storm could pose a serious threat to the levees on New Orleans’s West Bank — which largely survived Katrina — according to the Times-Picayune:

Hurricane Gustav will be at Category 4 strength with winds of 145 mph only 12 hours before it hits the central Louisiana coastline Monday afternoon, according to a 2 p.m. National Hurricane Center forecast.

On that track, a Louisiana State University coastal scientist says, storm surge could reach the top or overtop levees on the West Bank, could raise water to 8 feet — plus waves — along levees on the Mississippi River-Gulf Outlet, and combined with a water-swollen Tchefuncte River, could push surge into Madisonville on the Northshore.

Water also could rise as high as 8 feet in the Industrial Canal, he said.

“With the new intensity and based on earlier model data I received from sources outside the state, we could expect to see surges in the Houma area that are going to be as high as some of the levees there, up to 10 to 11 feet,” said Ivor van Heerden, a coastal geologist who serves as deputy director of the Louisiana Hurricane Center at LSU.

“The bottom line is that what Katrina and Rita didn’t destroy in 2005, this storm has the potential to do,” he said.

Van Heerden warned that several levee reaches around Houma face open water, and the diagonal direction of the storm will make them perpendicular to the waves, “and we could see a very erosive wave field set up.”

National Hurricane Center Senior Hurricane Specialst Richard Knabb said Gustav’s unexpected rapid intensification to Category 4 strength today as it approached Cuba’s western tip foretells a second explosive rise in intensity when it reaches the central Gulf of Mexico.

The official forecast has Gustav reaching Category 5 strength with winds of 161 mph by 8 a.m. tomorrow and then very slowly losing intensity. It will still be at 145 mph at 8 a.m. Monday, when it is about 100 miles south of the mouth of the Mississippi River.

Storm surge height are governed by the combination of windspeed around the center of the storm, the storm’s intensity that causes its center to have lower air pressure that pulls the water surface upward, and by the storm’s motion as it moves toward the coast.

During Hurricane Katrina, scientists say, the surge height was increased by the hurricane’s high winds and intensity while still 12 hours off the Louisiana coast, a condition similar to what Gustav promises.

“Surge levels at the West Bank will be at or very close to the crown of the levee and there will be a wave field of two or three feet of waves on top, hitting every six seconds,” Van Heerden said. “A ery erosive situation.”

Because of the storm’s northwest track through the Barataria and Atchafalaya basins, areas with large areas of wetlands and open water, high surge is now expected between Raceland and Lake Charles, he said.

Thankfully, the evacuation effort is well underway in New Orleans:

As of noon today, the city-assisted evacuation plan, implemented at 8 a.m. this morning, has moved about 2,700 people out of the city on buses and one train, with at least 20,000 more registered for assistance, New Orleans and state officials said at a midday press briefing.

Mayor Nagin said the evacuation seemed to be “working according to design,” despite two obstacles regarding pet evacuations and the city’s 311 evacuation registration system, and he strongly urged residents to leave the city as soon as possible.

“I am strongly, strongly, encouraging everyone in the city to evacuate,” Nagin said. “Start the process now.”

Nagin especially warned tourists to leave the city, particularly the large amount of visitors in town for the Southern Decadence festival.

“It’s time for you to leave the city. All tourists in the city, I’m asking you to start the proces of evacuation,” Nagin said, also urging Southern Decadence officials to cancel scheduled events immediately.

So far, the biggest glitch in the city’s evacuation plan has been registering evacuees with the city’s 311 system, which crashed overnight as the number of registrants surged from 13,000 to 20,000, Nagin said. In response, Gov. Bobby Jindal ordered that the 311 registration process be suspended, said Nagin, who added that only residents needing medical assistance during evacuation need to use the 311 registration system. All other city-assisted evacuees will instead be registered “on the back end” once they have reached a shelter, Nagin said. The city expects the total number of city-assisted evacuees to reach 30,000 at least.

“But even if the number’s bigger than 30,000, we have some contingency plans,” Nagin said.

Buses will continue to shuttle between the city’s 17 evacuation sites and Union Passenger Terminal, where evacuees will be taken to shelters in north Louisiana and Tennessee. He reassured evacuees that everyone taken out of the city will have a ride back.

Nagin announced that a bus company contracted by the city to carry out pet evacuations failed to show up this morning, and that state vehicles and the fire department have stepped in to solve the problem. The mayor did not release the name of the bus contractor or why the company did not fulfill their contract.

Contraflow could be implemented to speed an evacuation as soon as this afternoon, but will most likely begin tomorrow morning, Nagin said.

A mandatory evacuation has not yet been issued, but Nagin said that, at the earliest, he will announce one at 7 p.m. tonight to go into effect at 8 a.m. tomorrow. After a mandatory evacuation has been issued, anyone not on their own property after curfew will “in all likelihood be arrested,” said New Orleans Police Superintendant Warren Riley.

A strong National Guard presence is developing, with several intersections in the area of the Superdome blocked off by military personnel. Fifteen-hundred New Orleans police officers are expected to be on duty, with 1,500 to 2,000 National Guard soldiers in the city already. By comparison, about 1,200 NOPD officers were on duty for Hurricane Katrina, with only 300 to 400 National Guard soldiers, Nagin said.