Scientist Dr. Chris Landsea talks about hurricanes from the National Hurricane Center in Miami.


The biggest threat to Delaware so far this hurricane season, Hurricane Earl, may have missed, but the season on the whole has been an exciting one for the scientists at the National Hurricane Center in Miami.

With two months left until the season closes in November, NHC scientist Dr. Chris Landsea shared some inside knowledge about the severe storms.

Q Are some storms easier or more difficult to forecast than others?

A Some storms are substantially easier to forecast on their track — where they’re going to go over the next four or five days. The reason for that is [a hurricane is] skewed by the large-scale winds around it, kind of like a leaf in a stream. Sometimes we know exactly where the stream of air is going to push the hurricane, other times it’s much more unclear. Often that uncertainty comes when there’s a dip in the jet stream. The good news is, we’ve gotten a lot better in a short number of years. Our average error right now for a two-day forecast is about 100 miles; 20 years ago it was double that. The same is not true for the windspeed forecasting; we’re still having a lot of difficulty in making skillful predictions of how strong the winds will be.

Q Why do hurricanes only come around during a certain time of year?

A You get about 90% of the hurricanes in just August, September and October. The reason for that is there are a few key ingredients that have to be in place in the hurricane recipe for them to occur, one of which is warm waters. The threshold is 80 degrees Fahrenheit. We have 80-degree water in the Caribbean all year round, but we don’t have hurricanes all year round; it’s just one of the factors. One of the other big factors is what the winds are doing aloft. If you have a lot of windshear — that’s changing speed and direction — that can tear apart a hurricane. Ironically, hurricanes like a quiet environment to grow. They also need moisture; if they don’t have the thunderstorms, they will not develop.

Q How will global warming affect the hurricane season?

A Global warming, in my view, is a real concern. We are seeing changes to the atmosphere and the ocean; roughly, it’s warmed up about a degree Fahrenheit in the last few decades. Hurricanes are heat engines, so one might expect hurricanes to be stronger or more numerous or longer-lived. We test that with various computer models of the climate now and in the future. When you look at the sensitivity, it’s not really what you’d expect. What we see is that the seasons won’t last any longer, the number of storms will stay the same or even go down. The computer models suggest there will be more of that windshear tearing apart storms. But, the ones that are out there, because there’s more energy for them to tap into, they could get a little stronger — on the order of about 5% stronger 100 years from now.

Q How do you come up with the yearly list of hurricane names?

A It’s a six-year rotating list; the names we used this year are the ones we used back in 2004. If a particular storm is very destructive or hurts or kills a lot of people, the country that got hit, their weather service can request to retire the name. In 2004, you had Charlie, and that was replaced by Colin this year. Because the Atlantic, Caribbean and Gulf of Mexico have English speakers, Spanish speakers and French speakers, we use a mix of English, Spanish and French names.

Email Doug Denison at doug.denison@doverpost.com.