Those dire warnings that worldwide warming was having an incendiary effect on hurricanes and that ever-more powerful, deadly, and costly tropical storms were inevitable were part of the legacy of Katrina's almost unimaginable devastation.
But what followed was shocking for other reasons: After that 2005 season, not a single major hurricane struck U.S. shores, constituting a period of record quiet. Technically, Sandy, as bad as it was, was not a hurricane at landfall.
If forecasters can be believed — and last year they whiffed badly — this could be yet another relatively tranquil season in the Atlantic basin, which includes the Caribbean Sea and Gulf of Mexico.
Experts say the lull represents the calm between the storms, and a bleak-or-bleaker debate continues over whether the Atlantic basin will be a busy tropical-storm brewery for perhaps the next two decades — or in perpetuity.
With an estimated $10 trillion worth of insured property in hurricane-target areas, the outcome is of importance not only for coastal residents and property owners, but for every U.S. taxpayer.
From fiscal 2005 through 2013, hurricanes consumed more than $60 billion in federal disaster money, 75 percent of all Federal Emergency Management Agency aid, or about $500 per U.S. household. That doesn't capture the full tally for the hybrid storm Sandy, or the estimated 24 billion tax dollars all but lost to the U.S. Treasury by the National Flood Insurance Program.
Historically, active hurricane periods have alternated with quieter ones in 25- to 40-year cycles, based on government records. From 1970 to 1994, hurricane traffic generally was slow. But according to the government's Hurricane Research Division, an active period began in 1995 and could last perhaps 20 more years.
The last several years notwithstanding, more tropical storms mean more opportunities for damage, even if not all those storms qualify as "major" hurricanes. Besides Sandy, there was Irene, in 2011, which made landfall in North Carolina as a minimal Category 1 hurricane but cut a destructive path; Allison, in 2001, one of the deadliest storms on record, never reached hurricane status.
The research division attributes the uptick to the "positive phase" of something called the Atlantic Multidecadal Oscillation, or AMO, characterized by generally warmer waters in the Atlantic.
That analysis, however, "is wrong," in the view of Pennsylvania State University's Michael Mann, a respected — and controversial — figure in the climate-research community. It was Mann who gained unwanted fame when he was implicated in the "climategate" scandal in which leaked e-mails suggested data tampering. The university cleared him of wrongdoing.
Mann, along with other researchers, holds that the AMO, a complicated phenomenon, actually entered a cool or "negative" phase in the 1990s and that, in essence, warming from greenhouse emissions has masked it.
"The warming is extremely unlikely to reverse," he said recently; in short, this is not a "phase," and things are likely to get worse.
"It's difficult to say for sure whether we are currently in a positive or negative phase of the AMO," said Gregory Foltz, at the Atlantic Oceanographic and Meteorological Laboratory. He noted that other experts had documented that the oscillation indeed has been in its warm phase.
Although the rate of global warming evidently has slowed in recent years — and Mann thinks that, also, is related to the AMO — climate scientists have calculated that overall, Earth's temperature has risen at the rate of about 0.25 degrees Fahrenheit in the last 30 years.
But if that warming is somehow increasing hurricane intensity, the evidence has been wanting in recent years.
No major hurricane, one with winds of at least 111 mph, has made landfall on a U.S. coast since Wilma, in 2005. No hurricane of any intensity has hit Florida in that time. Both are records, according to Dennis Feltgen, meteorologist and official spokesman at the National Hurricane Center in Miami.
Last year, despite forecasts of a brisk season, only two hurricanes formed in the Atlantic basin, the fewest in 31 years, and for the first time since 1994, not a single major hurricane developed.
The criterion for a name for a tropical storm is a peak wind of at least 39 m.p.h. The threshold for a hurricane is 74 m.p.h. The normal tallies for a season are 12 named storms, six hurricanes, and three major ones.
Forecasters say it's possible that the tranquility will lap into this season, which began June 1 and ends Nov. 30. The key might be thousands of miles away in the tropical Pacific. An El Niño, in which warmer-than-normal sea-surface temperatures cover a continent-size area of the Pacific, might be unfolding. The warm waters' interactions with the atmosphere generate powerful upper-air winds from the west that can snuff out incipient storms in the Atlantic.
Millions of people along the Gulf and Atlantic coasts will be rooting hard for El Niño.
©2014 The Philadelphia Inquirer