Chris Landsea: Busy 2011 Atlantic hurricane season

NOAA predicts a busy 2011 season for Atlantic hurricanes. EarthSky spoke about it with Chris Landsea of the National Hurricane Center.

The U.S. National Oceanic and Atmospheric Administration (NOAA) predicts a busy 2011 season for Atlantic hurricanes. EarthSky’s Jorge Salazar spoke with Chris Landsea, the science and operations officer at the U.S. National Hurricane Center, about the science behind predicting hurricanes.

Eye of Hurricane Katrina. Image Credit: NOAA

What’s important for people to know about the 2011 Atlantic hurricane season?

A hurricane strike at any individual place is a very rare event, whether it’s a busy or a quiet year. So with this outlook, we really can’t answer the question of who’s going to be hit this year. All we can say is, it looks like it’s going to be a busier overall season.

How should people use NOAA’s hurricane forecast?

For any individual homeowner, families, small business owners, we would not want them to make any change to their preparations for this hurricane season based on the outlook we just issued. Because, for example, last year it was very busy overall, but we had no U.S. landfalling hurricanes.

Conversely, you can have a relatively quiet season, like 1992, which was predicted to be a very quiet year, overall. There were only four hurricanes. But if you lived in Miami-Dade County, it was the worst hurricane you ever experienced, when Andrew came roaring ashore.

We really don’t want most people to really change anything for their preparations. What we want people to be aware of is that hurricane season is coming, [hurricane season started June 1st] and to really have a plan for what to do when a hurricane threatens your community.

What weather and climate elements now will have the biggest influence on hurricanes in 2011?

There are two main factors that we’re looking at for the seasonal hurricane forecast for the Atlantic this year. The first is that we’ve been in a La Niña event. La Niña is cooler than normal waters in the eastern Pacific. That actually has a remote effect where cooler waters there promote more hurricanes in the Atlantic, because it tends to reduce the amount of wind shear that tears apart the storms and allows more thunderstorms to develop. We had been in a La Niña, and that was one of the reasons 2010 was so busy. It does appear that there will be some lingering effects from the La Niña as it starts fading away.

The second factor is, we’ve been in an enhanced activity since 1995, both because of the reduced vertical wind shear as well as warmer waters. And that appears to still be in place for 2011 as well.

Image Credit: NASA

How is the hurricane forecast generated? What scientific data is used to generate the NOAA seasonal hurricane forecasts?

First thing we do when we’re putting together the seasonal outlook is to examine all the environmental factors that we know affect hurricanes. We’re looking at the wind shear, that’s the changing winds with height throughout the atmosphere. We’re looking at the ocean temperatures. And we’re looking at this big phenomenon, called the El Niño and La Niña, and seeing if it’s going to be switching at all. We’re putting a lot of that information into statistical techniques – whether it’s an analog technique – or we’re looking at past years most similar to 2011 – or a little more sophisticated regression models.

In the last couple of years, we’ve also been getting output from various climate models themselves, where various groups integrate forward in time for the next several months what the weather patterns may be. They’re suggesting this year that we will not have an El Niño and that we’ll have an active hurricane season. We’re getting these model outputs from the climate forecast system, from the U.S. National Weather Service. We’re getting climate model outputs from the European Center for Medium Range Forecasts. And we’re also getting the U.K. Met office’s seasonal output. We’re putting a little more emphasis in the last couple of years on these more sophisticated, full physics computer models.

In addition to using the latest scientific instruments, such as weather satellites and underwater thermometers, NOAA is involved in what’s called the Atlantic Hurricane Database Re-analysis Project, which looks at historical records of hurricanes. What does the past tell us about future hurricanes?

The re-analysis of the Atlantic hurricanes is a project where we’re going back to old hurricanes, all the way back to 150 years ago, and trying to obtain all the observations – whether from ships or from coastal stations or more recently from aircraft – and re-evaluate them in terms of our understanding today of how hurricanes work and how they track. The reason for doing this is that in planning for the future, you really need to understand how the past has gone.

For example, if you’re trying to figure out what building codes are most appropriate in the coastal zones, you need to know how often you get strong hurricanes and what is the strongest hurricane that could occur in that area. Likewise, for insurance companies to correctly assess the risk and to charge the right amount for insurance rates, they need to know how often hurricanes are going to blow buildings down. Having this accurate record in the past allows different users, like building codes and insurance companies, to better plan for the future.

We have seen some incredible destruction, whether it was Hurricane Andrew in 1992 or the multiple strong hurricanes that struck in 2004 and 2005 or Gustav and Ike in 2008. Every time we get a landfalling major hurricane, we’re seeing tens of billions of dollars of damage.

And one might think that this trend for more damage may be linked to the warmer waters of global warming. But really, you have to take a more detailed look at what’s going on. Why are we having more damage? And there are two big reasons why. One is that the per capita wealth keeps going up in the United States, one generation after another. Compared to when our grandparents were our age, we have four times the amount of goods. We have bigger houses, more cars, lots of stuff inside the homes. So when a hurricane hits, there’s a lot more stuff that could be destroyed.

And as important, if not more important, is that populations are just skyrocketing in the coastal areas. And that’s both in the United States and in our neighbors in the Caribbean and Central America.

So after you take into account the societal effects that increase damage, you take those out and try to say, well, if strong hurricanes in the past hit today, what kind of damage might they do – you don’t see any trend. What you instead see is a swing, back-and-forth between decades, when there’s a lot of hurricane destruction and then decades that are relatively quiet. It matches perfectly with the U.S. land-falling hurricane record. It also matches perfectly with records for the whole Atlantic – tropical storm and hurricane numbers after you account for ones that were likely missed because we haven’t had satellite imagery, for example, before 1975.

That’s a big issue, the damage and the destruction that hurricanes can cause. And again, it has been going up. But it’s an effect of society, and it’s not an effect of the changing hurricanes themselves.

Get information from NOAA on preparing for a hurricane here.

Listen to the 90-second and 8-minute interviews with Chris Landsea on what’s predicted to be a busy 2010 hurricane season (at top of page.)

Jorge Salazar