How will Ida compare with Katrina?

Hurricane Ida is expected to make landfall Sunday, threatening to bring dangerous wind, storm surge and rain to the Gulf Coast exactly 16 years after the arrival of Hurricane Katrina, one of the most costly natural disasters in American history, which left more than 1,800 dead and did more than $100 billion in damage.

The overall impact of storm surge from Ida is predicted to be somewhat less severe than that from Katrina. The 2005 storm was blowing at Category 5 strength in the Gulf of Mexico before weakening as it approached landfall, so it generated enormous storm surge, reaching more than 20 feet in parts of the Mississippi coast. Current projections put the potential storm surge of Ida at 12 to 16 feet.

“Fifteen-foot sure can do a lot of damage,” said Barry Keim, a professor at Louisiana State University and Louisiana State Climatologist. “But it’s going to be nothing in comparison with Katrina’s surge.”

Improvements to the levee system following Katrina have made the New Orleans metro area better prepared for storm surge. But the areas that are likely to receive the most severe surge from Ida may be less equipped to handle it than the area that was hit by Katrina, said Dr. Keim.

Ida is expected to make landfall to the west of where Katrina struck, bringing the most severe storm surge to the Louisiana coast west of the Mississippi River rather than east of the river, as Katrina did.

“We are testing a different part of the flood protection in and around southeast Louisiana than we did in Katrina,” Dr. Keim said. “Some of the weak links in this area maybe haven’t been quite as exposed.”

While the impacts of Ida’s storm surge are expected to be less severe than Katrina’s, Ida’s winds and rain are predicted to exceed those that pummeled the Gulf Coast in 2005. Ida is expected to make landfall on the Gulf Coast as a Category 4 storm with sustained winds around 150 miles an hour; Katrina came ashore as a Category 3 with winds of 125 m.p.h.

“It could be quite devastating — especially some of those high-rise buildings are just not rated to sustain that wind load,” said Jamie Rhome, acting deputy director of the National Hurricane Center.

The severe damage from Hurricane Laura, which struck southwest Louisiana last year as a Category 4 storm, was caused primarily by high winds. The storm caused 42 deaths and damage costing more than $19 billion.

Ida’s rainfall also threatens to exceed Katrina’s highs.

The National Hurricane Center estimates that Ida will drench the Gulf Coast with 8 to 16 inches of rain and perhaps as much as 20 inches in some places. Katrina brought 5 to 10 inches of rain, with more than 12 inches in some areas.

“That is a lot of rainfall,” Mr. Rhome said of the forecast for Ida. “Absolutely the flash flood potential in this case is high, very high.” Combined with storm surge, he said, that much rain could have a “huge and devastating impact to those local communities.”

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