New hurricane rating system needed

There”s word out today that Katrina was “weaker” than first thought when it struck the Louisiana / Mississippi border. The final analysis showed it came ashore as just a Category 3 hurricane. Measurements in New Orleans showed peak winds of just 95 miles per hour.

The initial reaction from this revelation has been that it shows how inadequate the hurricane protection system in New Orleans was. Quoth Sen. Mary Landrieu:

“This news further highlights the need for a full federal commitment to build the highest level of protection through levees and coastal restoration for New Orleans, South Louisiana and the Gulf Coast.”

It”s an easy equation on the surface: New Orleans was supposed to be protected against a Category 3 storm, but the levees failed when the city was on the weak side of a Category 3 storm – therefore protection against a Category 3 storm isn”t enough.

But the real story here is how useless the 1 to 5 rating system for hurricanes really is. Hurricane Charley made landfall in Florida last year as a Category 4 storm. And as bad as the damage was near Tampa, it was very localized destruction caused primarily by wind – which is typical for hurricanes.

Katrina, on the other hand, was anything but typical. I”ve written before about the unimaginable scope of damage in Mississippi (10-foot surge 2 miles inland). When we drove down to Louisiana for Thanksgiving, we stopped in Mobile to eat at the relocated Original Oyster House and we took pictures of the destruction there.

This is what used to be a gas station next door to what used to be the Original Oyster House across the channel from the U.S.S. Alabama in Mobile Bay:

Katrina”s surge simply washed away all but the concrete frame of the buildings there – about 100 miles from where the storm made landfall. If this is a “Category 3″ storm”s effect, Hurricane Andrew (a solid “4″) should have wiped out the Florida coast from Homestead through Miami, Fort Lauderdale, West Palm Beach and up to Jupiter. But it didn”t.

And New Orleans should have been safe from a “Category 3″ storm. But it wasn”t.

That”s the problem Katrina exposed. Assigning a 1 to 5 rating to a hurricane really tells us nothing. Hurricanes cause wind damage, surge damage and rain-based flood damage. Yet the wind speed is all that goes into the rating people use to gauge their reaction to the threat.

Katrina was a “5″ at one point, and that”s what prompted the evacuation of New Orleans and caused people in Mississippi to pay attention. And surely the intensity the storm reached out in the gulf had a direct effect on the ultimate destruction. Had it carried much of its surge without stretching beyond a “3″, however, a lot more people would have stayed put – and died.

And now people will say the New Orleans protection failed even when the city was on the backside of a Category 3 storm. And they”ll say that means they need Category 5 protection.

The engineers who designed – and will redesign – the New Orleans protection system surely don”t just think “Category 3″ when they”re drawing up plans. They design for water height, pressure and other forces. They may be told “we need Category 3 protection”, but they translate that into what the forces are likely to be in those conditions.

The National Weather Service also tracks much more information about storms than just wind speed. They measure barometric pressure, ocean wave heights, etc. They know how big the storm is and how fast it”s moving, which forecasts localized rainfall and the potential for flooding. Yet the headline term that most people pay attention to is the category rating.

And considering the Hurricane Center folks always have to remind people that even a Category 1 hurricane is dangerous, it”s clear too much attention is paid to the wind-speed number.

So as the U.S. looks at the legacy of Katrina, one change should be a more informative and precise storm categorization system. Getting the public, FEMA, local officials and relief agencies to look beyond the wind number would help everyone better prepare for storms and make relief and recovery more focused and effective.

Maybe what we need is a multi-number system that rates wind, surge and rain. Katrina might have been a 3-5-2 storm in such a system, and nobody would be surprised at the destruction.

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