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Bill Chameides

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Welcome to Hurricane Season Circa 2012

Posted: 06/06/2012 6:10 pm

A hard rain's gonna fall. Question is how hard and how often.

June 1 marks the official start of the Atlantic hurricane season. This year the atmosphere kind of jumped the gun by spawning two named Atlantic storms -- Alberto and Beryl -- in May. That fast start out of the gate notwithstanding, the official hurricane forecasts for 2012 envision a fairly ho-hum year: see here, here and here. For example, the forecast by the National Oceanic and Atmospheric Association has a 70 percent chance of:

  • nine to 15 named storms (with minimum wind speeds of 39 miles per hour),
  • four to eight hurricanes (with minimum wind speeds of 74 miles per hour), and
  • one to three major hurricanes (Categories 3 to 5 with minimum wind speeds of 111 miles per hour).

The seasonal average for the past 30 years is 12 named storms, six hurricanes, and three major hurricanes.

One of the factors that affected this year's forecast is another forecast: that an El Niño may develop over the course of the summer. Turns out that El Niños tend to suppress hurricane activity in the Atlantic.

With memories of the catastrophic hurricane seasons of 2004, 2005 and 2008 (the three most costly on record) still fresh, the predictions for an average season are quite welcome. But two recent publications suggest that we are far from being in the clear when it comes to hurricanes.

Holding On to Beaches in the Face of Hurricanes Getting More Difficult

In May, the U.S. Geological Survey released a report on the vulnerability of Gulf of Mexico beaches to hurricanes. The study, based on more than a decade of measurements and detailed modeling, came to a conclusion that I at least don't find terribly surprising: Virtually all of our beaches along the Gulf Coast are at risk.

It won't take much, either. More than 99 percent of beaches are vulnerable to erosion and damage from a direct hit by the least intense (Category 1) hurricanes. Twenty-seven percent of those beaches are likely to be inundated where the "beach and dune are completely and continuously submerged" by water and waves. As hurricane intensity increases, so does the likelihood of damage: with the most intense (Category 5) storms, almost 90 percent will be inundated. If you live on the Gulf Coast, you'll probably want to check out their interactive map (and get more info on it here.).

Of course, given our level of coastal development, we rarely give up on a beach these days, even after it has been washed away by a storm or slowly eaten away by erosion. Beach preservation or, more properly, restoration is a happening thing in the USA. It even has its own national association: the American Shore and Beach Preservation Association. And with the triple whammy of storms, sea level rise, and coastal development, the association has been busy, as has the Interior Department's Bureau of Ocean Energy Management. According to Greenwire, the amount of sand mined from the outer continental shelf to reseed East Coast beaches has more than doubled on an annual basis in the past nine years as compared to the previous eight.*

A Hurricane-Global Warming Link

We can all agree that, for the most part, intense hurricanes are bad news. Even worse news would be that hurricanes are getting more frequent or more intense as a result of, for example, global warming.

So are they? Turns out that that is a question being hotly debated by the scientific community. (See here and here.) A number of investigators have analyzed decadal trends in the number of tropical storms and/or their intensity, and have concluded that they are on the rise and in some cases correlated with rising ocean temperatures. Others have come to the opposite conclusions.

One of the reasons why it has been so hard to reach a consensus is that the studies have been based on counting the number of storms or the number of storms of a given intensity over a period of decades -- a period when our ability to track and characterize storms has greatly increased. It is hard to determine if an apparent trend found in the data is real or just an artifact from the changing measurement systems.

A new study by C. M. Kishtawal of the Space Applications Centre in Ahmedabad, India, and colleagues reported last week in the journal Geophysical Research Letters took a somewhat different approach. Rather than consider whether there was a change in the number of storms, they assessed whether the rate at which storms form was changing.

The authors looked at satellite-derived storm track data over the global ocean basins from 1986 to 2010 -- a period with the most reliable data. They then limited their analysis to those storms that exceeded a peak wind speed of at least 80 knots (making it a Category 1 hurricane) and looked at two periods in a storm's genesis: 1) from tropical storm stage to hurricane stage, and 2) from hurricane stage to its peak intensity. What they found on average was that the time it took for storms to move to peak intensity, once they had become hurricanes, had gotten shorter -- or, put another way, the rate at which a storm grew in intensity had increased. The most extreme example of this was in the North Atlantic basin where the average time needed for a storm to intensify from a Category 1 to a Category 3 storm was reduced by nearly 20 hours over the study period.

Interesting result, but perhaps even more interesting is what it implies about the intensity of hurricanes. Through additional analysis and modeling, the authors found that the increase in the rate at which storms grew also increased the likelihood of the storm reaching a greater peak intensity. Overall that implies that for a given hurricane season, there may not be any more storms than in past years, but of those that do occur, there will be a shift away from Category 1 and 2 storms toward more Category 4 or 5 storms. And if the past is the key to the future, that suggests we may see even more frequent Category 4 and 5 storms in the coming decades.

So what does all this mean for this year's hurricane season? Hard to say, but if storm clouds are headed your way, I advise you to follow the advice my mom used to give me those many years ago: Son, take cover 'fore the rain starts a fallin'.

_____________________

End Note

*All that beach preservation comes with a price tag. Data maintained by the Program for the Study of Developed Shorelines at Western Carolina University indicates that a total of $3.5 billion has been spent on known beach replenishment in 20 states since its inception.

Crossposted with The Green Grok | Facebook.com/deanchameides

 

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