Minimal-Hurricane Isaac Could Be Over-Achiever in Damages

Shortly after midnight today, August 29, 2012, NASA's Suomi-NPP satellite captured this moonlit view of Hurricane Isaac and the cities near the Gulf Coast of the United States. The slow-moving storm made landfall as a category 1 hurricane near the mouth of the Mississippi River in southwestern Louisiana at about 6:45 p.m. local time on August 28, 2012. Image courtesy of NASA.


Hurricane Isaac is on the bottom rung of the scale used to rank hurricanes’ destructive potential, but the damage it inflicts on the U.S. Gulf Coast during the next 24 hours could make it an over-achiever.

Hurricane Isaac made landfall late yesterday afternoon in southeastern Louisiana as a minimal hurricane with winds of about 80 mph (129 kph). Jeff Masters, director of the website Weather Underground, said Isaac’s damage could be U.S. $2 billion to $5 billion.

If the damage from Isaac reaches $5 billion, that would earn the storm a slot among the 25 most destructive hurricanes in U.S. history. Such a ranking would put Isaac ahead of some hurricanes that were much more powerful at landfall.

Isaac was a Category 1 hurricane on the Saffir-Simpson Scale, which ranks hurricanes from one to five based on their destructive potential. A Category 1 hurricane has maximum winds of 75 mph to 95 mph (121 kph to 153 kph), while a Category 5 hurricane has maximum winds exceeding 155 mph (250 kph).

“Category 1 is not a very good measure for Isaac,” Masters sai.

Isaac’s slow pace as it moves inland will be the cause of the damage. As of about 11 a.m. EDT today, Isaac was moving northwestward across southeastern Louisiana at only abut 5 mph (8 kph). Hurricanes’ forward movement often speeds up after they make landfall, but Isaac’s slow crawl means that southeastern Louisiana will be subjected to Isaac’s high winds and drenching rain for a day. And that relentless pounding of wind and water will cause problems, Masters said.

“There will be considerable wind damage,” Masters said. “Not devastating wind damage, but widespread damage.”

Isaac’s storm surge — a mound of water piled up by the storm’s winds and pushed forward as it comes ashore — also is causing problems. The Times-Picayune newspaper of New Orleans reported today that the surge, as much as 12 feet (3.6 meters) in some places, has already overtopped  about 18 miles of levees along the Mississippi River in Plaquemines Parish, which is south of New Orleans.

Masters said the overtopped levees in Plaquemines Parish were not part of the multi-billion-dollar upgrade to levees after Hurricane Katrina devastated the area in 2005.

Emergency management officials in Plaquemines Parish could not be reached for comment.

But the levees in New Orleans that catastrophically failed during Hurricane Katrina seven years ago have withstood Isaac’s assault so far. Billions of dollars were spent to repair and reinforce the levees and install new flood control equipment to protect New Orleans after Katrina.

“The fact that the levees in New Orleans haven’t failed yet is great news,” Masters said. “The highest danger point has passed. But this is a long duration, and a lot of times the failure comes after levees have been pounded for many, many hours. There’s a lot more of this event to come.”

Despite the damages caused by Isaac, there could be some benefit from the storm’s heavy rains, which could be more than a foot (about 30.5 centimeters) in some places. The rainfall could help ease the drought in several Southern and Midwestern states as it moves inland later this week.

“How much is rain worth?” Masters said. “It’s gotta be worth billions.”

Willie Drye has been writing about hurricanes and other topics for National Geographic News since 2003. Visit his blog, Drye Goods.

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Willie Drye is an award-winning author and a contributing editor for National Geographic News. He and his wife live in Wilmington, North Carolina.