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The worst by far in Katrina was the storm surge, which I still haven't seen definitive numbers for, but which was certainly over twenty-five feet, and maybe even thirty feet. That wiped out the Mississippi Gulf Coast (I mean total devastation), and it is what caused the levy breeches in New Orleans, and the destruction of Slidell.
The only places you have to worry about the storm surge, though, are low-lying areas affected by the tides. Bayous, bays, and of course, the Gulf. The wall of water from the Gulf in Katrina went inland maybe a mile in most places, and most of the destruction was on the Gulf and the bays where the surge hit unabated, for about half a mile inland.
After that, the storm surge caused damage, but less, except in one place behind Bay St. Louis and Waveland, where the area is riddled with harbors and bayous. There, the storm surge didn't hit like a tsunami, but the waters rose to the full height of the surge (in this case, that was over twenty-five feet, and I don't normally believe these numbers, but i saw a friend's house that had water to the ceiling, at least 25 feet off the ground.) and washed inland probably ten miles. I've seen many hurricanes, and I've never seen anything like that.
Keep in mind Katrina's surge was literally unprecedented.
Hurricanes also cause wind damage, flood damage from rain and rivers, tornadoes, and on rare occasions, lightning.
So if your area floods during big storms, a big hurricane might flood it worse. With Houston's record of flooding, a strong hurricane could be very, very bad in certain areas. The storm surge keeps the rivers from emptying into the gulf or bay, and the rain (if there is a lot) floods the rivers, and the water can back up very, very quickly, almost like a tidal storm surge. I'd be very woried if you live in an area that floods if this thing heads directly at you, especially if it heads into the bay. Keep in mind that the day after the hurricane can bring more flooding as the storm floods the rivers inland, which then wash down to the coast.
Remember the hurricane a few years ago that went inland around Brownsville and caused almost no damage, but then went inland and flooded all the rivers, causing a wall of water to come back down the Rio Grande and destroy a lot of property from behind. That's a real danger with Houston, because of the rivers and bad drainage.
Tornadoes are tornadoes. Katrina had a lot of them. Not all hurricanes do.
The constant is the wind, and the weather service will tell you the strength, but not the duration. Katrina had milder winds than some hurricanes, but it was so big that the wind was continuous for seven or more hours. That is also almost unheard of. So trees and buildings that survived strong winds from smaller hurricanes fell in Katrina because of the constant winds, combined with the long rain softening the ground around the roots.
The damage inland with Katrina was mostly wind, and some tornado. I drove through some of those regions, and a lot of buildings were torn apart from the wind (mostly tin roofs, and a lot of missing shingles, but I did see some rather respectable size houses completely destroyed.) But the worst damage inland was falling trees. Pine trees can slice a house in half if they are big enough. Plus, they fall on power lines and cars and roads, and that's what does the most harm. Some parts of Louisiana and Mississippi 100 miles inland are still without electricity, water, phone, supplies, and so far, government assistance. That's why Maddy McCall hasn't been posting, I suspect.
Anyway, that's the danger areas. Add to that the human dangers of looters (yes, white people in rural and suburban areas loot) if the damage is bad enough and law enforcement can't get there for a few days.
So you decide your danger zone. If you stay, stock up on a week of food and two weeks of water, and remember, the Red Cross and FEMA are stretched very thin right now.
Oh yeah, and the waters of the Gulf are very hot right now, after years of drought and above average temperatures (maybe global warming, who knows?). So this hurricane will strengthen, and be really mean, unless some front manages to destroy it. The weather service isn't predicting that to happen, though.
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