First, I’m not a meteorologist. I’m a bureaucrat for the City of Houston. (Just ask Foghat!) I write to entertain and and inform (whether you or me is a question I can’t answer), and my opinions should not be taken as anything but that; do not treat my words as sources of wisdom on which to risk or save your life. But one of those car-window-shattering tools could be a really good investment right now if you live in Texas.
The one thing I don’t rely on for information is any TV station or cable channel. Let’s face it, they want to sensationalize and keep you hanging, so they dribble out the information in tiny bits and fill in with things you don’t need to know, but they assume you will find interesting. When I want to know something, I want information, not “human interest angles” and some pretty/handsome talking face breathlessly expounding someone’s latest “worst possible outcome.” Let’s not even mention the incredible amount of bullshit and fakery coming out of Fakebook and Twit-talk. This nonsense is dangerous and misleading; it promotes attitudes like mine, only worse. But….the stupidest thing you can do is assume that because the media (and lying liers) are always hyping is that it is nothing but hype, every time. It isn’t. And this is one of those times that it is likely to not be hype.
As a resident of Houston since 1985 and having survived several hurricanes (plus drawing on my brother’s experiences in 1983′s Alicia), I can say this: Harvey is a once-in-a-generation occurrence. Hurricanes might slow down, but loops and stalling like we’re seeing develop here normally do not happen over land. When they do happen (which is rare) it’s usually in mid-ocean, and nobody but a few ships are inconvenienced. Back in 2001, Allison dumped 12-36 inches of rain in 24 hours, and as it happened, I was in one of the areas getting 36″. The crazy thing was that the three meso-cyclones (basically, circular eddies) that spun off from Allison after it was no longer a named storm, were all located over the Greens Bayou and Carpenter’s Bayou watersheds. They stretched over the White Oak, Buffalo, and Braes Bayou watersheds as well, which is what inundated downtown and the Medical Center. Then the storm moved off, giving us a day and a half of respite before moving back on Monday for an encore performance of 5″-11″.
But Harvey, while it won’t match the one-day performance of Allison, will hit a MUCH more widespread area, and add a not-negligible storm surge with it. If, as some tracks predict, it hovers on the edge of the shore, or parallels it (on or off) while slowly moving towards Houston, the winds on the right side of the hurricane will continue to drive a storm surge onshore. Think “localized global warming sea level rise of 5 feet” and you’ll start to get the picture. Now add four days of heavy rain, adding one to three feet, completely saturating the ground. How much the soil can absorb is dependent on the soil type, elevation, water table, rate of rainfall, and prior absorption. A very rough rule of thumb is that the maximum the ground can take (hereabouts, YMMV) is about 1″ an hour for about two hours. Then the street flooding starts. After that, assume absorption of a 1/4″ an hour. Of course, the amount of asphalt and concrete make a difference…and we’ve added a lot in some critical places over the last 15 years.
Because of the “hype” tendency and fragmented information presented by TV reports, when I want to know how much rain we’re getting and what the current state of affairs is in the bayous, I go to the source — the Harris County Flood Control District Flood Warning System. For the effects of traffic, I use the Inrix iPhone traffic app, or check the direct feed from Houstontranstar.org online.
More later, I need to stop being a bad employee and go do some work.
Update: Bad for another moment — meant to point out that I usually try to find some other blogger with more expertise to check with; Brenden Loy seems to have gone on to a real job, so this time it’s Levi at www.tropicaltidbits.com. His is the only place I’ve been able to find the actual model tracks from the earlier post.