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Tropical Storm Debby was a storm for the ages

If you're trying to come up with excuses for the inundation of your roads or water-containment ponds, the phrase "100-year storm" comes in pretty handy.

That's what I thought, anyway, when John Burnett, Hernando County's water resource coordinator, used those words recently to explain why the rain from Tropical Storm Debby overwhelmed the Peck Sink project southwest of Brooksville. A spokeswoman for the state's toll roads did the same when talking about flooding on the northern section of the Suncoast Parkway.

It's nobody's fault, they seemed to be saying. It's just the weather.

Yeah, right, said I, a skeptic by temperament and profession.

Sure, there was a lot of rain. But could it really compare to some of the events I've heard about and even lived through? Could it be the kind of storm that happens once a century?

Actually, yes, though I first found out that "100-year storm" doesn't mean exactly that. It's technically an event that has a 1-in-100 chance of happening any given year, said Paul Close, a meteorologist and weather historian at the National Weather Service station in Ruskin.

Locally, that means a daily rain of more than 11 inches and a four-day storm of more than 16 inches.

In parts of central Hernando and western Pasco, Debby dumped more than 15 inches between June 23 and 25. And on June 24, a Southwest Florida Water Management District rain gauge near the flooded stretch of the parkway received more than a foot of rain — 12.24 inches. It was the highest one-day total ever measured at the 20-year-old gauge, and "it's right around the rainfall criteria" for a 100-year storm, Close said.

By another measure, Debby was not just a 100-year storm, but a 122-year storm. A rain gauge on Chinsegut Hill, north of Brooksville, operated from 1890 until earlier this year. Scientific continuity is one more casualty of the place's neglect. We can't directly compare June's rains to all of the previous ones.

But nothing at Chinsegut ever stacked up to the one-day total measured last month at the Swiftmud gauge a few miles to the west.

The top contender was a 10.22-inch rainfall Sept. 6, 1950, during Hurricane Easy, which, by the way, set a one-time national record by dumping 38.7 inches of rain in a 24-hour period at Yankeetown.

And as a multiday storm, Easy is aptly named in that it easily beat Debby with a four-day total of 20.21 inches at Chinsegut.

The floods of 1960 were bad enough to prompt the founding of Swiftmud. All of Wiscon Road near Brooksville was underwater, and 4 feet of water covered U.S. 41 at Powell Road, south of Brooksville, said Derrill McAteer, longtime chairman of the Swiftmud governing board.

To understand why, first remember that the 78 inches of rain that fell in 1959 was the most ever recorded in Hernando.

Then look at the list of major multiday rainstorms provided by Close. The second-biggest ever at Chinsegut came in March 1960, when a Debby-like 15.3 inches fell in four days.

The fifth-highest four-day total measured there, 11.48 inches, came in late July of that year. Then, in early September came Hurricane Donna and several more inches of rain.

Still, for a one-day rain, nothing in 1960 came close to Debby.

What about the big storms I've been here to witness? Well, the no-name storm of March 1993 gave us a lot of wind and a killer tidal surge, but not enough rain to make Close's list of the top eight events.

The El Niño winter of 1997-98 was remarkable for severe and widespread flooding, but the rains came in repeated storms that stretched from October through March, not one or two historic ones.

The rainy season of 2004, capped by tropical storms Frances and Jeanne, was robust enough to fill the Masaryktown canal. But as a four-day storm, Frances brought slightly more than 10 inches of rain to Chinsegut, considerably less than the highest totals for Debby.

It would probably take a lot more analysis of more sites to say for sure how Debby ranks among the biggest rainstorms in local history.

But for now, I've seen enough. A skeptical mind has been satisfied.

Tropical Storm Debby was a storm for the ages 07/14/12 [Last modified: Saturday, July 14, 2012 1:59pm]
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