Researchers, publishing their work in this chaotic hurricane season, have created a storm of their own. Two groups have found independently that over the last 30 years, hurricanes have steadily been gaining strength.
If Rita is a Category 4 storm when it reaches land, this will be the first year since 1915 that the U.S. has been hit by two storms of that intensity.
"The total number of storms that are reaching Cat 4 and 5, and the number of days that they are staying at Cat 4 and 5, is increasing substantially," said Peter Webster, a climatologist at the Georgia Institute of Technology, who led one study published in the journal Science.
Hurricanes get their fuel from the warm waters below them. This season, the Gulf of Mexico has been unusually warm.
In some places, the water temperatures in the Gulf have topped 90 degrees. The average is only about 1.4 degrees Fahrenheit above normal, but that warmth, spread over thousands of square miles, has helped make Katrina and Rita into very powerful storms.
"The Gulf waters have been getting warmer; in fact, in this past August 2005, we saw the highest temperatures in the Gulf for the last 25 years," said Menas Kafatos, director of the Center for Earth Observing and Space Research at George Mason University in Virginia.
Storms Pick Up Power in Gulf
Katrina and Rita started in the Atlantic Ocean but became strongest once they entered the Gulf of Mexico.
"It was the Gulf waters," Kafatos said, "that fed the two monsters and made them so strong."
But the Earth's climate is wildly complex, and scientists say there are even larger forces at work.
Some researchers point to global warming. Others say we are at the crest of a regular cycle -- that hurricanes fluctuate in number over a period of several decades.
They say the Atlantic was deceptively quiet until about 10 years ago.
"In 1995, it's just like somebody threw a switch here," said National Hurricane Center director Max Mayfield, testifying this week before Congress. "And we've had a lot more hurricanes -- not a record number of major hurricanes, but close."
This is already one of the four-busiest hurricane seasons in the last century -- and it still has five weeks to go.