IRA FLATOW, host:
This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. Later in the hour we'll be talking about keeping New Orleans and other coastal cities safe from hurricanes and rising sea levels, but first, last year was a record hurricane season, with seven major hurricanes; four of which hit the U.S. and certainly hurt the U.S. The hurricane season starts June 1st, right around the corner. What can we expect this year?
Joining us now to give us the 2006 hurricane forecast, back again is Gerald Bell, lead forecaster for NOAH's Seasonal Hurricane outlook at the National Weather Service's Climate Prediction Center, in Camp Springs, Maryland.
Welcome back, Dr. Bell.
Mr. GERALD BELL (Meteorologist, Maryland): Good to be here. Thank you.
FLATOW: It's becoming like, you know, we're following hurricanes like we never did before; predictions at least.
Dr. BELL: Oh, absolutely. We know more about hurricanes now than we ever have before, and our understanding of the climate patterns that control the seasonal activity is such that we can now make very highly accurate predictions of what the season will be.
FLATOW: How accurate? If you look back last year at this time, when you made your prediction for last season, how accurate were you?
Dr. BELL: At this time last year we indicated a 70 percent chance of an active season, and the season was certainly active. We had also indicated the high likelihood the season would be very active, and indeed it was.
But this early in the season, the climate signals don't really allow us to predict a record season such as we had.
FLATOW: So you're not making that prediction this year?
Dr. BELL: Well, at this time, no. While we're expecting a very active hurricane season again this year, we're not expecting levels comparable to last year's record season.
FLATOW: All right. So give us your best prediction for this year, then.
Dr. BELL: Well, right now we're expecting 13 to 16 named storms, of which we expect eight to ten to become hurricanes and four to six to become major hurricanes. So we're expecting a very active season.
And for these types of conditions, on average, two to four hurricanes strike the United States; so it' very important that people start to get prepared for an active hurricane season.
FLATOW: Now, how do you distinguish between a hurricane and a really - and a hurricane?
Dr. BELL: Well, a major hurri - there's hurricanes and then there's major hurricanes. A major hurricane is category 3 or higher.
Dr. BELL: …on the hurricane scale. And that's wind speeds above 111 miles per hour.
FLATOW: Mm-hmm. And what made last season so severe that you're not predicting to be equal this season?
Dr. BELL: Well, last year was a record season and resulted from a combination of four main factors. Only two of those factors are predictable at this time. Those two factors are very warm ocean waters continuing, and the wind and air pressure patterns that we've seen since 1995 that have been giving us a very active hurricane era are still in place. So the warmer waters with these on-going favorable conditions are expected to bring another very active season.
But there were other factors that just simply - that occurred last year that just simply cannot be predicted at this time.
FLATOW: Let's talk about them. What were they?
Dr. BELL: Well, one was suppressed rainfall, actually in the central Equatorial Pacific - not the Atlantic. That produces - when that happens that produces low wind sheer across the western Atlantic. That combination of lower wind sheer due to the suppressed rainfall over the Pacific and the ongoing patterns we've had since '95, are known to produce extremely active hurricane seasons.
FLATOW: Mm-hmm. What about the high pressure in the upper atmosphere in different places?
Dr. BELL: That was another factor that contributed to all - that also contributed to very low wind sheer. We had persistent high pressure in the upper atmosphere over the eastern U.S. for much of the season, and that helped to expand the area of low wind sheer and also to make the wind sheer even lower. And hurricanes love low wind sheer.
Low wind sheer - wind sheer refers to how the winds change as you go up through the atmosphere.
FLATOW: Right. Right.
Dr. BELL: Hurricanes require that there be a small change in winds. So the combination of factors led to…
FLATOW: (Unintelligible) lops off the top - lops off the top of the hurricane. Yeah.
Dr. BELL: …so all produced - contributed to exceptionally low wind sheer to a therefore a record season.
FLATOW: Now, we also saw in the Gulf that the Gulf waters were very warm. And once Katrina moved over Florida and came into the Gulf, it really blew up very quickly.
Dr. BELL: Well, that's correct. The Gulf of Mexico waters, once you get into the peak of the season, are generally around 84, 85, 86 degrees Fahrenheit. So that's very warm water. Typically, hurricanes form more in the central tropical Atlantic or in the Caribbean Sea, where the waters are not so warm. And relatively few move into the Gulf. But when they do move into the Gulf, and in addition into an area of very low wind sheer, that is certainly a recipe for major hurricane formation.
FLATOW: Now, those Gulf waters were over 90 degrees last year at the end of the season, weren't they?
Dr. BELL: They were actually about a degree, a degree-and-a-half warmer than normal. I don't recall the exact temperature.
Dr. BELL: But they were certainly warm enough to - 80 - anything like 85, 86, or even warmer is certainly sufficient to support a major hurricane. But it's not just the ocean waters alone. It - the hurricanes that move in the Gulf, they will dissipate if they run into high wind sheer.
FLATOW: Right. What about El Nino or La Nina? Any action for either one this year to affect the hurricane season?
Dr. BELL: There is no El Nino or La Nina in place at this time, and we don't expect either to be in place during the peak of the season. So we don't expect El Nino or La Nina to be a factor this year.
FLATOW: Mm-hmm. What should people do to prepare? I mean, aside from, you know, stocking up, doing the normal stuff that they do in hurricane season?
Dr. BELL: Well, that's one of the most important things to do, is to stock up with things that you feel you will need if the hurricane hits your area and you're without power for several days, without water for several days, and what have you - without toiletry items for children or babies, and things like that.
Another is the most fundamental thing: recognize that we're going to have another active hurricane season and that you need to start preparing. Often that doesn't even get realized. So the first step is to realize we're going to have an active hurricane season and therefore that means you need to prepare.
And not just individuals, but local governments, emergency management officials, all the way up the chain. As we see when these major hurricanes strike, these are not just local events. But the hurricanes can do tremendous damage well, well inland from where they strike.
FLATOW: Yeah. Is there a tip-off to you, as a meteorologist, something that might happen in a hurricane as the first hurricane forms, or in the way that it forms, that's going to send up a red flag to you to say, whoa-oh, this looks really like this season is starting off with a bang.
Dr. BELL: Well, the conditions that are setting up right now are already indicating a very strong likelihood that the season is going to be very active. We will continue to see the weather patterns evolve, to become even more favorable, as we go through the season.
Dr. BELL: Generally, the early season activity during June and July is really not an indicator of what we'll see for the season, as a whole. Some very active seasons you might see nothing during June and July.
However, as we saw last year, if we get some hurricanes forming in the deep tropics of the Atlantic, or even the Caribbean Sea, that's an indicator that the conditions are already - that the conditions that we expect are already extremely favorable, and when you see that, that's yet another tip off that the season is going to be very active.
FLATOW: Well, we'll keep an eye on it, and we'll have you back. I know you do an upgrade. Last year, you did an update about August, right?
Dr. BELL: That's right. NOAA will update its outlook again in early August. I don't believe we have the exact date specified yet.
FLATOW: All right. Gerald Bell, thank you for taking time to be with us.
Dr. BELL: It's a pleasure, thank you.
FLATOW: Talk to you later. Gerald Bell, lead forecaster for Noah's Seasonal Hurricane Outlook at the National Weather Service's Climate Prediction Center in Camp Springs, Maryland.