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Experts Say

Weather expert Michael Wyllie joined Weather Watch on October 22, 2004, for a live interview.

Question: What causes a hurricane?

Michael Wyllie: Basically, a hurricane forms when we have a tropical wave move off the coast of Africa. It moves in a westerly direction into the warm waters of the tropical Atlantic Ocean. This wave turns into a low-pressure system, and if conditions are just right, the low-pressure system can build strength and turn into a tropical cyclone and eventually become strong enough to become a hurricane. Some of the required conditions would be warm, tropical waters of 80 degrees Fahrenheit; high pressure in the upper atmosphere; and weak winds aloft so that it doesn't shear off the top of the system.

Question: What does the temperature, air pressure, moisture, and wind have to be for a hurricane to form?

Michael Wyllie: These can vary but usually the required temperatures are water temperatures more than air temperatures. The water temperatures really need to be around 80 degrees. Pressure usually needs to be around 1,000 millibars or higher when the system begins. For moisture, many times what we see in the beginning of a storm's evolution is thunderstorms develop so you have heavy rains before the system even has a closed low-pressure system. Winds, many times in the development stages of a tropical system, are below 30 miles per hour.

Question: How strong can hurricanes be?

Michael Wyllie: Hurricanes can develop into strong, category 5 storms, with wind gusts exceeding 200 miles an hour. Some of the super typhoons in the Pacific, which are the same as the hurricanes that we see here, have had sustained winds close to 200 miles an hour.

Question: How do hurricanes gain strength?

Michael Wyllie: Hurricanes gain in strength when they go over areas of warm water and low sheer in the upper atmosphere. Just the right types of conditions with warm water and weak wind shear allow them to strengthen. Sometimes during the life of a storm, they will move across these areas of very warm water near 90 degrees, and very low wind shear, and the storm can intensify rapidly. We saw that during Ivan, where the storm went over an island and lost strength, then gained strength when it went back over the water west of Florida.

Question: What was the biggest hurricane ever?

Michael Wyllie: In size, I would say Mitch — which was a storm that went into the Gulf of Mexico and did quite a bit of damage — was a category 5 and the size of the storm filled most of the Gulf as it moved towards South America. It was probably one of the largest storms we have seen in the last couple of years. It was over 500 miles across.

Question: How do you know all this stuff about hurricanes?

Michael Wyllie: I've been with the National Weather Service for 27 years and have spent the last 14 years as a Meteorologist in Charge. In the Northeast part of the country, I've been working in weather for the past 22 years in both Boston and New York. In order to learn more about hurricanes, you are basically going to learn math and science. You are working with the sciences but it's a lot of math and a lot of computers. Computers are very important for forecasting, and they are why we are able to create the models so fast. As the technology gets better, the models get better and faster.

Question: How do you track the hurricanes?

Michael Wyllie: We track the hurricanes through satellites, which are getting better and better with technology. At night we use infrared satellite pictures and during the day we use regular pictures. We are able to determine the periods of strengthening and weakening of these storms, which helps us determine the storm cycles and helps us forecast what to expect with the life of the system. Once they get closer to land, we use the hurricane hunters, which are reconnaissance planes that fly right into the eye of the storm and use dropsens. These are equipment packages that we release from the bottom of the plane. They fall through the storm and tell us wind speeds, temperatures, and pressure of the eye and the eye wall. Those are the two main ways we track hurricanes.

Question: Why do hurricanes show up on computers as a big, doughnut shape?

Michael Wyllie: They look like doughnuts because the eye of the storm is normally cloud-free and rain-free, and if you are in there, the wind speeds are pretty light. That is because the eye has the lowest pressure. Surrounding that eye is what we call the eye wall and that usually has the strongest winds and the heaviest rain of the hurricane. As you go away from the eye wall, the winds and the rains diminish. So what you see as a doughnut hole is the eye of the hurricane and the calm of the storm.

Question: How do they choose the names for the hurricanes? Does it take time or do they just throw in a name that comes to mind even if it's weird?

Michael Wyllie: the World Meteorological Organization (WMO) selects the names. They select 6 years worth of names for the Atlantic Basin and repeat the names every 6 years. If there is a significant storm they will actually retire its name like they do great ball players. "Hurricane Andrew" was retired in 1992 because it did so much damage to South Florida. This year they will probably retire a bunch of names. Once they retire a name, the WMO will meet again and pick replacement names.

Question: Why did all the hurricanes hit Florida so hard?

Michael Wyllie: Actually, it was very unusual for Florida to be hit this many times. It's only the second time in history that Florida was hit that many times. Some of the areas that were hit in Florida had not been hit in more than 50 years, including the area that was hit twice by both Frances and Jeanne. I think the last time that happened was in the 1800s. It was just an anomaly this year. It was just Florida's turn.

Question: Do you think we will be able to stop a hurricane or prevent them from happening?

Michael Wyllie: Back in the 1960s, they had a project called Storm Fury that tried to seed hurricanes. What they did was use chemicals to try and diminish the storm, but it didn't work and caused lots of destruction instead. What they found was you could make hurricanes, and even thunderstorms, lesser in one area but it would make it worse in other areas. They call it Weather Modification, and unfortunately it doesn't always work. I'm not saying it won't happen, but right now controlling hurricanes is something that has not been followed up on by scientists. Learn more about this in the National Weather Service's Hurricane Myths: Frequently Asked Questions.

Question: Have you been in a hurricane before? If yes, when and what was it called and how many?

Michael Wyllie: The first time I remember being in a hurricane was in 1960. It was Hurricane Donna and I was 7 years old and on Long Island. That's what got me into the field of meteorology. We had the eye of the storm pass over the house where I lived and we went outside during the eye, and all the kids were out swimming in the water in the street when our parents yelled at us to come back in because the storm was coming back. It was really cool. I was also in Hurricane Eloise my first day of graduate school at Florida State University. I was in Hurricane Gloria in 1985; I was in New York City at the time and we got the weak side of it. And that was it.

Question: Where is the best place to hide from a hurricane besides a shelter?

Michael Wyllie: If you are told to evacuate, do so. That's the first thing. If you have to evacuate, your best bet is to go inland to someone else's home. Shelters should be your last resort. If you are in your house and it gets really bad, go into an interior room without windows, similar to what you would do for a tornado. If necessary, go into an interior bathroom, and if you must bring a mattress to put on top of you when you hide in the tub.

Question: Why do you like hurricanes?

Michael Wyllie: I always found hurricanes really fascinating. They are able to spin up from nothing to a hurricane in a short amount of time. It is a unique weather event and it is something that is a rare event for us in the Northeast. There is something about the strength of these storms, and the way they come and go so quickly; I find them fascinating. Once you start studying them, it gives you respect for nature.

Question: Do you like your job?

Michael Wyllie: The job of a meteorologist is very exciting. It is something where you are interacting with nature and it's always different. No forecast is the same. Something is always different. Every time you think you have it down, something changes. When you think you have that snowstorm figured out and it's going to drop a foot of snow, it will turn and start to rain on you. It's never predictable.

Question: Are hurricanes classified the same way as tornadoes?

Michael Wyllie: No, they are different. A hurricane is a large tropical low-pressure system and is classified by the Saffir-Simpson scale from a category 1 to a category 5 storm where category 5 is the strongest. A tornado actually is spawned from a thunderstorm cloud. It is a much smaller-scale feature and the damage, while very intense, is much more localized. It is classified by what is known as the Fujita Scale, from the weakest F0 to the strongest F5.

Question: What are the categories of hurricanes?

Michael Wyllie: Category 1 is a minimal hurricane with winds of 74-95 miles an hour. Category 2 has winds from 96-110 mph. Category 3 is from111-130 mph and Category 4 is 131-155mph. Category 5 has winds greater than 155 mph. What is the difference among a typhoon, cyclone, and tropical cyclone? Cyclone is the generic name for a low-pressure system; all hurricanes and typhoons are actually cyclones. Winter storms are actually cyclones. Typhoon and tropic cyclone means the same thing. A typhoon is the same storm as a hurricane but it occurs in the eastern Pacific.

Question: What is a tropical disturbance?

Michael Wyllie: We have a list of stage development for a hurricane. The first stage is a tropical wave and that is just a curvature in the trade wind easterlies, which are winds from Africa towards Caribbean. If that tropical wave gets some thunderstorms to develop on it and they remain on that wave for more than 24 hours, that's a tropical disturbance. And this is what we track on the satellite, especially looking at the 24 hour time period. The next stage of development, when that disturbance begins to form a defined circulation and becomes a depression with maximum sustained winds of 38 mph, is called a tropical depression. When they are watching the depression and it gets to the point where it is beyond that stage, it becomes an organized system of thunderstorms where the winds are sustained 39-73 mph. Then it becomes a tropical storm and earns a name. Once the winds pick up to above 73 miles an hour, then you are in your hurricane.

Question: What is a tidal surge?

Michael Wyllie: A tidal surge is actually not a tidal surge. The surge from the hurricane is called a storm surge because it is an abnormal rise in the water level because of wind stress and pressures of the hurricanes. The highest surge is found to the right of where the eye of the storm makes landfall. We can see 10, 20, and even 30-foot surges in water just prior to the eye making landfall. If you have a strong hurricane with a 20-foot storm surge coming on shore, it will also have wind waves on top of it that will do a lot of the damage. That's why we evacuate people on the coastline during a hurricane.

Question: When meteorologists forecast, how can they tell what's going to happen 3 days before that specific date?

Michael Wyllie: We use numerical models. We have several of these models to assist us in our forecasting. We use information on the surface of the earth in addition to many levels above the surface of the earth that assist us in determining where low pressure systems will be in 1, 2, 3 and even up to 7 days in advance. This is what helps us determine where the cold and warm air will move across the country. Forecasting has become a lot more sophisticated even in the last 10 years due to the increase in technology. Now we put information into a database, and the computer gives the forecast and crunches the numbers for us.