The Weather Never Sleeps

You may have to act without all the facts

Figure 1: Hurricane Charley forecast, 5 p.m. on August 11. Red: hurricane warnings Pink: hurricane watches Orange dot: latest eye position Black dots: forecast eye positions

Figure 2: Hurricane Charley forecast, 5 p.m. on August 12. Red: hurricane warnings Pink: hurricane watches Blue: Tropical storm warning Orange dot: latest eye position Black dots: forecast eye positions

Figure 3: Charley's winds during storm's entire life Red: Hurricane force, 74 mph or stronger Orange: Tropical storm force, 39-73 mph

Dangerous weather often seems to sneak up on pilots.

For instance, scattered clouds covering less than half the sky below the airplane may slowly grow, covering more and more of the sky until the pilot who isn't qualified to fly in the clouds can no longer see the ground--as the fuel gauges inch toward empty.

Hurricanes are an exception. They are huge storms.

Unlike low ceilings and visibility, thunderstorms, and ice, hurricanes do not catch pilots by surprise. A search of the National Transportation Safety Board online accident files, which go back to 1962, turns up no cases of a pilot unsuspectingly stumbling into the worst of a hurricane's winds and rain. Only two reports list hurricanes as part of the cause of crashes. Both of these--one in Chatham, Massachusetts, in 1994, and one in Darien, Georgia, in 1964--occurred in low ceilings and visibilities far from system centers after the hurricanes had weakened to tropical storms with winds slower than 74 mph. Wind was not listed as a factor in either crash.

This doesn't mean pilots have no concerns about hurricanes. If you live anywhere near the U.S. Gulf or Atlantic coasts and own an airplane, you can have some hard decisions to make when a hurricane approaches. Individual pilots often have to balance flying an airplane to refuge with staying to make sure their homes and families are ready for the storm. If you decide to fly your airplane away from the storm, you'll almost surely have to take off when the odds are still less than 50/50 that the storm will hit your area.

To see how this works, imagine you are in Punta Gorda on Florida's southwest coast on Wednesday, August 11, 2004. You see on the local evening news that the National Hurricane Center has issued a hurricane watch for the Florida Keys and the state's west coast north almost to where you live. The watch means that 74 mph or faster hurricane-force winds could hit any part of the area under the watch within 36 hours.

The television weathercaster says Hurricane Charley is about 85 miles southwest of Kingston, Jamaica. It's barely a hurricane with 75-mph winds. The weathercaster seems to be taking it seriously and mentions that the National Hurricane Center says the odds are 29 percent that Charley's eye will pass within 60 miles of Fort Myers by Saturday afternoon. By then its fastest winds could be around 100 mph.

The weathercaster shows a National Hurricane Center forecast map with a black line indicating the path Charley's eye is forecast to follow right across your part of Florida Friday afternoon (see Figure 1).

The white area surrounding the black line indicates the area where the storm's eye could go. Even with satellite images, reports from hurricane-hunter airplanes, and sophisticated computer models, predicting a hurricane's exact path is still difficult. The white area reflects this by growing larger as time goes on.

You decide to keep an eye on Charley. As you finish breakfast Thursday morning you realize that you're going to have to decide what to do about your airplane in the next few hours.

You hear on the radio that a hurricane warning--meaning hurricane-force winds could arrive within 24 hours--is now posted for southwest Florida as far north as your area. Charley is still pretty far away, about 100 miles east of Grand Cayman Island in the Caribbean. But it is growing stronger with winds up to 85 mph, and the probability is now 34 percent that it will hit your area.

You sit down at the computer and call up the National Hurricane Center's Tropical Cyclone Forecasts and Advisories Web page. Here you see the three-day forecast and advisories map (see Figure 2, p. 54). It's much like last night's map, except the black line seems to be closer to Tampa Bay than where you live to the south. But, you heard Max Mayfield, the National Hurricane Center director, say on the radio, "Don't focus on the skinny black line." And, this morning's Hurricane Center probability is only 36 percent for the Tampa Bay area, compared with 34 percent for your area. You aren't about to bet your airplane a two-percentage-point spread.

The white areas on the two forecast maps convince you that your best bet will be to fly your airplane to an airport near a friend's house north of Birmingham, Alabama.

Even if Charley's path shifted and it hit near Mobile, Alabama (the chance of that is now only 2 percent) its winds will be much weaker by the time what's left of Charley reaches northern Alabama.

Here, as with almost all hurricanes and even tropical storms, the big danger would be heavy rain--but your destination is on high ground.

Fortunately, you won't have to worry about your family and house if you fly your airplane to Alabama. Your wife and children will go with you. Your house is away from the beach. Before you bought it, you looked at the maps at the county's emergency management office showing which areas could flood in storms. You also made sure that your house was built to withstand strong winds. Finally, you installed metal shutters for all of the windows and a sliding glass door. You will roll these down before you leave. And you've installed a tested, impact-resistant cover to keep debris blown by a hurricane's winds from breaking down the garage door, letting the wind in, where it can push up on the roof; you'll put it in place before leaving.

In strong winds, a building's roof can act like a poorly designed airplane wing, creating enough lift to pull the roof off the building if it's not firmly attached. Wind coming in battered-down garage doors or broken windows pushes the roof up from below, making it even more likely to go sailing away to smash into a neighbor's house.

You know that if Charley hits your area with 100-mph-plus winds, you and your family should be safe in your house. But after the wind ends, you could go to the airport to find that the roof of the T-hangar that held your airplane has been peeled back, allowing it and parts of your airplane to fly away.

The decision is to go and you and your family are in the airplane headed for Alabama before noon. You could have waited, but you wanted to make the trip in daylight.

You decided you couldn't wait until Friday morning to leave because the Thursday morning forecast (Figure 2) showed that by Friday morning, Charley should be centered between Cuba and Key West, close enough for its outer bands of rain and gusty winds to be hitting your area.

Here's what happened as you waited out Charley in northern Alabama:

Just after 2 a.m. Friday, one of Charley's outer rain bands swept across the Fort Myers airport with lightning and winds gusting to 29 mph. The weather calmed down later that morning, but intermittent rain with stronger and stronger winds continued all day.

Around 2 p.m. Friday the Hurricane Center reported that a hurricane-hunter airplane had measured winds up to 145 mph near Charley's center and the hurricane was heading for the Punta Gorda area. Charley came ashore a little before 5 p.m. and continued heading toward the northeast across Florida, leaving destruction behind.

Getting out well before the storm is often the best decision, but it's not an easy decision to make. Hurricane Charley turned out to be a good example of what can happen when people in the possible path of a hurricane don't follow Max Mayfield's advice not to "focus on the skinny black line."

After you returned from Alabama your neighbors were talking about "Charley's abrupt right turn."

But, when you looked at a map showing Charley's path, you didn't see any abrupt turn (see Figure 3). Curious about this, you got out a World Aeronautical Chart that shows Florida's West Coast and the eastern Gulf of Mexico and plotted some positions.

First you looked up tracking information on Charley on the Hurricane Center Web Site and marked the locations of the storm's eye at 5 a.m., 1 p.m., and 5 p.m., after it was ashore, on August 13. Using your navigation plotter, you then found the compass heading the storm took from the 5 a.m. position to the 5 p.m. position and from the 1 p.m. to 5 p.m. positions.

You then found the compass headings Charley would have taken from the 5 a.m. and the 1 p.m. positions if it had gone to Tampa International Airport.

The change in course from 5 a.m. for Charley to go to Punta Gorda instead of Tampa was 7 degrees. The course change for Charley to go to Tampa instead of Punta Gorda beginning at 1 p.m. was 10 degrees. Neither is much of a change.

In fact, if Charley had been a student pilot taking the flight test for a private pilot certificate, a 10-degree course change would have been well within the limits of course deviation expected for the basic instrument maneuvers and navigation portions of the test. The Private Pilot Practical Test Standards say that during some navigation tasks, the pilot should maintain heading within plus or minus 20 degrees.

If you're ever faced with deciding how to react to a hurricane's threat, take note of watches and warnings, use the Hurricane Center probabilities to help you decide what to do, and, finally, don't focus on the skinny black line.

Jack Williams is coordinator of public outreach for the American Meteorological Society. An instrument-rated private pilot, he is the author of The USA Today Weather Book and The Complete Idiot's Guide to the Arctic and Antarctic, and co-author with Bob Sheets of Hurricane Watch: Forecasting the Deadliest Storms on Earth.

For more on hurricanes, see AOPA's aviation subject report.