Hurricane Katrina slammed ashore at the Louisiana and Mississippi Gulf coast on Aug. 29 as a Category 4 storm with 140 mph winds, killing at least 1,036 people and triggering a monumental relief effort.
Hurricane Rita, which followed Katrina by weeks, registered as the third strongest Atlantic Ocean storm in history -- a Category 5 packing 175 mph winds -- during its trek across the Gulf of Mexico before it lost some of its ferocity as it approached the Texas and southwestern Louisiana coast.
With hurricane names already reaching R, there's a chance the alphabet will run out before the hurricane season does on Nov. 30. If so, the National Weather Service will start naming the storms after the Greek alphabet for the first time ever.
A study published in the Sept. 16 journal Science says the number of Category 4 and 5 storms occurring worldwide has nearly doubled during the last three decades.
In the 1970s, there were about 10 Category 4 and 5 hurricanes each year around the world. Since 1990, the number reached 18 annually, the researchers from the Georgia Institute of Technology's School of Earth and Atmospheric Sciences and the National Center for Atmospheric Research found.
A Nature study published in July found similar results. Both studies were funded by the National Science Foundation, which also funds the NewsHour's Science Unit.
The largest increases in the number of severe hurricanes were plotted in the North Pacific, Southwest Pacific and the North and South Indian Oceans, with smaller increases in the North Atlantic Ocean, the Sept. 16 study says.
The number of severe hurricanes in the North Atlantic, which is usually behind the other oceans, increased by only a small amount -- about 5 percent -- with winds gaining a tiny, perhaps 1 mph margin, said Chris Landsea, a meteorologist at the National Hurricane Center in Miami.
The research shows evidence of natural hurricane cycles, rather than a gradually trending upward, Landsea said. Hurricanes can have extremely busy 10-to-15-year cycles followed by periods of 25 to 40 years of quiet, he explained.
Conditions that are ripe for hurricanes include warmer waters and less wind sheer to tear up the swirling storms, said Landsea.
And this year, which is already in a busy portion of hurricanes' natural fluctuation, has the right pressure patterns in the Atlantic, lack of El-Nino, and the presence of areas of warm water to spawn such major storms, said Ken Reeves, a senior meteorologist at Accuweather.com.
Compounding the problem is that coastal areas are becoming more populated, resulting in "horrific" damage when the storms do hit, said Landsea. "In the 1940s and 1950s (a previous active cycle), there weren't that many people living in harm's way," he said.
Reeves said it's hard to tell in advance how long the busy hurricane period may last. Some projections say the current pattern began in 1995, others in 2000, he said, which means the Atlantic may not be getting a reprieve any time soon.