Hurricanes Bret, Floyd and Irene, along with Tropical Storms Dennis and Harvey, struck the mainland United States during 1999, killing 60 people directly (and more via indirect causes). The storms caused and estimated $1.7 billion in insured damage and nearly $4 billion in total damages, according to preliminary figures from the National Oceanic and Atmospheric Administration (NOAA). Final totals typically fluctuate for months as claims are processed.
The 1998 Atlantic hurricane season, also more active than normal, brought 14 tropical storms, of which 10 became hurricanes, including three major hurricanes that inflicted $7.3 billion in damages and caused 23 fatalities in the United States. Overall, tropical cyclones claimed an estimated 11,629 lives in 1998 -- 11,000 due to hurricane Mitch in Central America. Not since 1780 has an Atlantic hurricane caused so many deaths.
Looking back at the forecasts
Nature cooperated with two separate forecast teams in 1999.
In May, a group of NOAA scientists issued their first-ever hurricane season forecast, which called for an above-average season of more than 10 tropical storms, six hurricanes and at least three major hurricanes.
Colorado State University Professor Bill Gray, long considered the guru of long-term tropical forecasting, made a similar forecast along with a large team of researchers.
Gray's team called for 14 named tropical storms, nine of which would become hurricanes and four of which were expected to become major hurricanes.
Looking back on the season, the folks who bring us the forecasts were pleased with their efforts, but noted once again that even the best forecasts don't prevent damage.
"Hurricanes Floyd and Irene are cruel reminders that hurricanes can produce tragic loss of life and devastating economic disruption from inland flooding beyond a hurricane's damaging wind, storm surge or tornadoes," said D. James Baker, NOAA administrator and under secretary of commerce for oceans and atmosphere. "The tragic loss of life and economic disruption caused by Hurricane Floyd's widespread flooding from eastern North Carolina to New England and the rainfall from Irene reminds us that we cannot lower our guard for the seemingly weak storm."
Why so busy?
As expected, hurricane activity has increased in recent years, in part because of changes in long-term climatic cycles. Since 1995, Gray and others have been saying that conditions are ripe for a return to more active hurricane seasons, a periodic shift that could last two or three decades.
With the period from 1995 to 1998 being the most active four-year period on record -- yielding an average of 8.3 hurricanes a year, compared with a normal of 5.8 -- the evidence favoring the beginning of a busy stretch is strong.
"I think we're in a new era for storms," Gray said in April. He pointed to known historical cycles to buttress his argument that nature is at a turning point.
Two lengthy periods this century saw relatively mild activity -- 1900-25 and 1970-94. In between, from the early 1930s through the late 1960s, more active seasons were the rule.
While many factors control the number of hurricanes in a given season, Gray has said the long-term trend is ruled by a conveyor belt of sorts that moves Atlantic Ocean water northward, from near the Caribbean to an area east of Greenland. There, the current sinks deep, moves southward, then flows into the southern Atlantic Ocean and beyond. It is the northward moving, warm surface water -- fuel for any hurricane -- that helps produce strong storms.
Recent measurements show that the water in the conveyor belt contains more salt than normal. This increases the water's density, researchers explain, causing it to sink to greater depths. This in turn increases the flow of deep water southward, which forces an increase in the flow of warm, tropical surface water northward. Thus, the northern Atlantic becomes warmer than normal, providing the heat needed to make hurricanes into powerful killers.
In the shorter term, La Niña gets some of the blame.
During an El Niño event, energy from warm water in the Pacific is transferred high into the atmosphere and funneled, in the form of strong winds, eastward, where it settles over hurricane-forming regions of the Atlantic, thousands of miles away. The settling of this air tends to choke hurricanes in their infancy.
La Niña, on the other hand, allows Atlantic hurricanes to develop their potential with less inhibition. La Niña conditions persisted through the summer and into this winter. If El Niño returns by next season, as expected, it could have a throttling effect on Atlantic hurricanes, though no predictions have been made yet. (Gray's early forecast for 2000 is due on December 8.)
Details from the 1999 season
Hurricane Floyd threatened Florida in September as a strong Category 4 hurricane with 155 m.p.h. (250 kilometers per hour) winds. Floyd turned north and northwestward while slowly weakening to a Category 2 hurricane. As it paralleled the southeastern coast from Florida to the Carolinas, emergency management triggered the largest coastal evacuation in recent U.S. history.
Floyd eventually made landfall near Cape Fear, North Carolina on September 16, producing massive inland flooding. The death toll of 56 makes Floyd the deadliest U.S. hurricane since Agnes in 1972.
Hurricane Irene formed October 13 and passed over Cuba and the Florida Keys. After crossing the Keys, the Category 1 hurricane made landfall on Florida's southern tip. Torrential rains of 10 to 20 inches fell on densely populated areas in Miami-Dade and Broward Counties, causing urban flooding not seen in the area since Tropical Storm Dennis in 1981.
Irene claimed eight lives, which officials say were indirectly related to the storm, and caused damage estimated at $800 million, mostly from crop destruction.
Hurricane Bret, which ran from September 18 to 22, reached a peak intensity of 150 m.p.h. (240 kilometers per hour) (Category 4 on the Saffir-Simpson hurricane scale). With winds of 125 m.p.h., Bret made landfall in a sparsely populated area midway between Brownsville and Corpus Christi, Texas.
Hurricane Lenny, a very unusual west-to-east moving low latitude hurricane, battered portions of the Caribbean in mid-November. On November 17th, Lenny was a strong Category 4 Saffir-Simpson storm with winds of 150 sustained m.p.h.
advertisement
