Inland areas next in line for flooding

Heavy rains threaten area from Miss. to Ohio

Hurricane Katrina

August 30, 2005|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

With Hurricane Katrina finally ashore, forecasters turned their attention yesterday to the dangers of inland flooding as the storm's remnants threatened states from Mississippi to Ohio with heavy rain.

They said Katrina's remnants would drop 4 to 10 inches of rain as they move north and east through western Tennessee, Kentucky, Indiana, Ohio and northern New York state, then into Canada.

Marylanders face a "slight" increased risk of severe thunderstorms from Katrina, mostly west of the Blue Ridge.

"It's going to be moving slow enough to put down enough water to have local flooding, but fast enough that you don't have catastrophic flooding in all the rivers," said Frank Richards, a hydro-meteorologist at the National Hydrologic Information Center.

All along its path, he said, "there can be pockets of very heavy rain, where the creeks go up and somebody, unfortunately, tries to drive through it. And that will be the last trip they take in a car."

The dying hurricane also could spawn tornadoes as it churns inland. But the greatest danger to human life from such storms is freshwater flooding.

Government data show that 59 percent of deaths from tropical cyclones in the United States from 1970 to 1999 were caused by freshwater flooding. High winds, surf and storm surges caused 24 percent.

Nearly two-thirds of the fatalities occurred in inland areas.

Hurricane Floyd, in 1999, brought intense rain and record flooding to the East. Inland flooding caused 50 of the 56 storm deaths.

In 1994, Tropical Storm Alberto dropped more than 21 inches of rain in Americus, Ga. - 180 miles from the sea - drowning 33 people.

Katrina began weakening yesterday before making landfall southeast of New Orleans. Top sustained wind speeds dropped from 175 mph at midday Sunday to 135 mph about the time of landfall.

The storm was downgraded to a tropical storm at 7 p.m. last night, with sustained winds below 74 mph, as its center moved through eastern Mississippi.

It remained a very wet system, barging inland at 15 to 20 mph. It is expected to carry tropical storm winds and heavy rain north into western Tennessee by this morning before diminishing to a tropical depression. It could reach the Great Lakes states by tomorrow morning.

As the system moves toward upstate New York and Canada, it will become extra-tropical, meaning that it will lose its spiral symmetry and merge with other weather systems, said Chris Sisko, a meteorologist at the National Hurricane Center.

"It's not going to linger, but the potential for heavy rainfall is still there," he said.

The greatest risk of significant inland floods is along rivers such as the Tombigbee and the Pearl, which flow from Tennessee, Alabama and Louisiana into the Gulf of Mexico.

"Most of the flooding on the Pearl and the Tombigbee will be minor and occasionally moderate," Richards said.

The threat of river flooding will diminish in Tennessee and points north and east, Richards said.

Much of Katrina's inland rain this week will eventually find its way back to the Mississippi via the Ohio and Tennessee rivers. But Richards does not expect renewed flooding in New Orleans when the water returns to the river's southern reaches.

"The Mississippi is a huge river," he said. It would take flooding in two of the system's three main feeders - the Missouri, Ohio and upper Mississippi - to cause flooding at New Orleans.

"Mother Nature dug the river channel pretty good. I don't expect to see main-stem flooding in the Mississippi at all with this storm," Richards said.

Some of the rain will be welcome.

"The good news is a lot of areas in Tennessee, Ohio and Kentucky have been dry," Richards said. "That's one of the reasons we're not looking for terribly significant flooding. The rivers are low, and the soil is dry."

But moisture will come at a price if the rain comes down faster that it can be absorbed and residents find their homes and vehicles surrounded by high water.

Flooding kills an average of 127 people a year in the United States, compared with 73 killed by lightning, 65 in tornadoes and 16 in hurricanes.

More than one in five people killed by tropical cyclones nationwide drown in their vehicles or while attempting to abandon them after driving into high water on roads.

"People have a little more confidence than what conditions call for," Sisko said. "They usually stall their cars and can't get out or get stuck in fast-moving water."

It takes surprisingly little moving water to sweep cars and people away. As water rises, it presses against an increasing area of rubber, steel and flesh, exerting more and more force. At the same time, water, sand or mud decreases the friction that usually holds tires and shoes to the pavement.

Gradually, the force exerted on the vehicle or pedestrians by moving water exceeds the friction holding them in place, and they're swept away.

As little as six inches of fast-moving water can knock an adult off his feet, and as little as a foot of water can shove most cars off the road, the National Hurricane Center said.

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