Major Hurricanes Predicted to Increase in Years Ahead

Hillary Mayell
for National Geographic News
July 20, 2001
Violent winds, killer waves, torrential rains, and flash flooding are the calling cards of a hurricane.

And if scientists are correct,the North Atlantic, Caribbean, and Gulf of Mexico regions can expect increased hurricane activity in the next 10 to 40 years.

The number of major hurricanes has more than doubled in the last six years. The increase is part of a long-term climate shift that is likely to persist for several decades, said Chris Landsea, a meteorological researcher with the U.S. National Atmospheric and Oceanic Administration (NOAA) Hurricane Research Division and co-author of a study on the findings in the July 20 issue of the journal Science.

"We've seen a big increase in the number of hurricanes since 1995, and in the next 30 years we're going to see a lot more," he said. "It's part of a natural cycle, and it's going to be a real eye-opening for the people living on the coasts who have never seen a hurricane before."

The findings may be a cause for concern, the researchers warn, saying those responsible for emergency preparedness and civilian safety should reevaluate current response strategies to insure they are adequate.

Tracking Patterns

Until now, the conditions responsible for the formation of tropical storms have been poorly understood.

A lack of sufficient data and the complex interactions between wind, water, temperature, and other factors that contribute to the development of a storm have made storm prediction a risky endeavor.

By using a combination of satellite imagery, computer modeling, and high-tech monitoring of numerous factors—from sea-surface temperatures to atmospheric conditions—the team of scientists has identified a multi-decade pattern of likely hurricane activity. These long-term patterns can be classified as quiet, near normal, or active.

During the 20th century, a period of high hurricane activity occurred from the 1920s through the 1960s, followed by reduced activity from 1971 to 1994.

The researchers predict that we are now on the cusp of a 10- to 40-year shift toward increased frequency of hurricanes.

"During any of these periods, the actual number of storms can jump around a lot from year to year," said Landsea. "1997 is a good example. Strong El Niño effects suppressed hurricane activity for that year even though we were in the middle of an 'active' period."

The long-term average is about ten storms a year, with about one and a half developing into "major" hurricanes, Landsea noted. "That number is likely to increase to three per year in the next several decades," he added.

Tropical cyclones undergo a series of phases—from tropical depression to tropical storm—before being defined as a hurricane.

Once a storm is designated a hurricane, it is measured on a scale from one to five based on wind speed (the Saffir-Simpson Scale). Storms designated as Category 3 and above are considered major hurricanes. A Category 3 storm has wind speeds of 110 to 130 miles per hour.

The new findings apply only to the Atlantic Ocean, the Caribbean, and Gulf of Mexico. Accurate records of hurricane activity date back 60 years for the Atlantic Ocean and the western Northern Pacific Ocean, but only about 30 years elsewhere. The lack of reliable records makes it impossible to identify long-term trends in other regions of the world.

Planning Ahead

The researchers warn that the long period of generally low hurricane activity from 1971 to 1994 may have lulled us into a false sense of security.

"We're looking at up to a five-times increase in damage costs from hurricanes," said Landsea. "Over the last 30 years we've been fortunate, with annual costs to the continental U.S. at about $500 million. That's likely to increase to about $2.5 billion."

The toll is much higher in other affected regions. In the Philippines, about 5 percent of the gross national product is spent on hurricane recovery. More than 10,000 people died in Honduras and Nicaragua when Hurricane Mitch struck in 1998.

The loss of human lives and damage to property can be expected to rise in the years ahead because of population growth, increased affluence, and greater development of infrastructure in many coastal regions over the last 40 years.

The extended period of generally reduced hurricane activity in recent years may have lulled hurricane-prone regions into a false sense of security, Landsea suggested. He said governments may need to rethink their emergency plans to determine whether they would be adequate if hurricanes in the next several decades become as severe as those of 1920 to 1960.

Co-authors of the scientific report were Stan Goldenberg, a meteorologist at the U.S. National Oceanic and Atmospheric Administration, Alberto Mestas-Nuñez of the University of Miami, and William Gray of Colorado State University.

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