Hurricane Katrina and the Intensifying Coastal Threat

This week Cyclone Center introduces Hurricane Katrina (2005) as one of our featured storms.  This is the 8th anniversary of Katrina’s assault on the northern Gulf of Mexico coast.  The city of New Orleans, despite a massive system of protective levees and pumps, lost over 1500 souls, almost all from drowning when water flooded about 80% of the city.  Since then,  millions of dollars have been spent on the repair and upgrade of the levee system in and around metro New Orleans.  Are they ready for the next one?

“We’ll be absolutely ready for it,” said U.S. Army Corps communications officer Wade Habshey in a recent Discovery News article. “What we have in place now can withstand a Katrina-level storm.”

New Orleans flooding caused by 60 kt. winds, 10-14 ft. storm surge. Category-5 values: 140 kt winds, 25-35 ft. storm surge.

But what exactly is a “Katrina-level” storm?  Winds in downtown New Orleans rarely exceeded minimal hurricane force at the peak of the event.  Storm surge and the strongest winds from the weakening Katrina were focused well to the east in coastal Mississippi.  And yet levees failed, water flooded significant portions of the city, and over 1,500 perished.

An even bigger concern in the long-term are geological changes occurring in the area; coastal portions of Louisiana are sinking into the ocean as climate-forced sea levels continue to rise and land areas sink.  This exacerbates the threat of  hurricanes for a region that experiences one on average every couple of years.  Many climate scientists now believe that hurricanes will be stronger on average in the future as the ocean, which provides the fuel for the storms, continues to warm.

What more should be done?  Government officials exude confidence that the improvements to the levy system will hold up, but we’ve heard that story before.  Claims were made soon after Katrina that the levee system was designed to withstand a Category-3 storm , not something like “Katrina’s strength”.  We’ve already seen that Katrina wasn’t even a hurricane in New Orleans – what happens when a real Category-4 or 5 storm hits the area?  We can only hope that residents will have left, because it’s a very good bet that there will be little dry land to stand on.

– Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

New Developments on Tropical Cyclones and Climate Change

One of the goals of the Cyclone Center project is provide a more definitive answer on how tropical cyclones (TCs) have been responding to the dramatic changes that our climate is undergoing.  It is difficult for meteorologists to determine how strong tropical cyclones are getting because we rarely observe them directly, relying primarily on satellite data to give us a decent estimate of the wind speeds.  But as you can imagine, it is very hard to determine the maximum winds in a hurricane when you are in the hurricane itself, let alone flying more than 22,000 miles above it!  Our record of tropical cyclones is by no means nailed down.

Hurricane Sandy and Climate Change – Checkmate?

During election season I will occasionally tune in to a few of the news networks to get my 10 minute dose of partisan noise.  As Hurricane Sandy churned in the Atlantic and aimed herself at the New Jersey coast, I happened to come across a show that featured an economist and a political analyst discussing the nuances of tropical cyclones and climate change.  I don’t recall exactly what was said, but it went something like this:

Economist: Sandy is huge!  Why isn’t anyone talking about climate change?

Analyst [very eager to break in to the conversation]: “Yes!  Look at Sandy – an ‘S’ storm!  When was the last time we’ve had an ‘S’ storm in the Atlantic?  Usually we only make it to the H’s, or I’s, or K’s.  Look at 1992 – the ‘A’ storm that year didn’t form until mid-August!”

Now I’m sure both of these gentlemen are very bright people and I have a lot of respect for the analyst (when he talks about politics), but having them discuss hurricanes and climate is like me commentating on a grandmaster chess match – I know how the pieces move but that’s only 10% of the battle.

There was nothing particularly unusual about Sandy in the beginning – we have seen plenty of hurricanes form in the deep tropics in October, and she moved and behaved in a pretty typical fashion.  Nor has there been anything outright weird about the 2012 hurricane season in the Atlantic Ocean.   Before the season, every documented seasonal forecast of the number of named storms was above the long-term average, and the season has played out accordingly (even exceeding expectations in many cases).

But a season is usually remembered by one or two storms, and Sandy has made 2012 quite historic.  Weather forecast models accurately predicted days in advance that Sandy would have a major impact on the northeast United States.  And judging by the images and stories coming out of New Jersey, New York, and surrounding states, Sandy lived up to expectations.

As with any major storm or weather event, the inevitable question is asked: “Did climate change cause/enhance this?”  Although a definitive answer is elusive (we don’t have a big enough laboratory to create a “warming free” experiment), we can make a reasonable assessment about some of the factors that probably played a role.

Individual storms such as Sandy respond to the instantaneous ocean and atmosphere environment they find themselves in – or in a way, weather.  Climate is the palette, not the paint; it sets the scene for the actors to do their part.  So what was Sandy’s “scene”?

We know that the world’s oceans are warming – warm water means more energy is available for the hurricane.  We know that sea levels are rising, leading to larger hurricane storm surges.  And we know that coastal development continues to expose millions of people to storms like Sandy.

Most climate scientists believe that we are in for stronger hurricanes in a warmer world and that we are already seeing a move toward this new era.  But our data are just not good enough to know for sure if tropical cyclones have already been becoming stronger.  Almost all tropical cyclones, even in recent years, are not measured directly; and even when they are, we can only measure small samples of these vast storms at any one time.  This is a big reason why there are conflicting accounts on recent tropical cyclone trends.

Cyclone Center was created to help resolve these questions.  By having the public analyze 30+ years of tropical cyclone images, we will provide meteorologists with new data that can be used to reconcile differences in individual storms, as well as long-term trends.

And by the way, the last year with an ‘S’ storm in the Atlantic was 2011.  And that ‘A’ storm in August of 1992, one of only six named storms that year?  Hurricane Andrew, a category-5 storm that devastated South Florida.  To those residents affected by Andrew and Sandy, climate change is a secondary concern.

– Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville

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