Tropical Storm Isaac remains at the very cusp of hurricane status, declared “nearly a hurricane” as of 7:00 AM. Its barometric pressure remains more typical of a Category 2 hurricane, and the most recent NHC discussion, at 5:00 AM, stated that “THE INNER CORE CIRCULATION IS BECOMING BETTER DEFINED…AND STRENGTHENING MIGHT BE IMMINENT.” (Stop me if you’ve heard that one before. What a confounding storm to forecast!) Yet for now, on the morning of the day it will hit the U.S. mainland, Isaac remains stuck at 70 mph. I confess I’m a bit surprised the NHC hasn’t just gone ahead and declared it a hurricane — it’s so close, either decision would probably be justifiable — and then let the year-end Tropical Cyclone Report retroactively downgrade it if necessary. But they’re playing this one by the book.
Whether it hits as a 70 mph tropical storm or a 75 mph hurricane, Isaac’s effects will largely be the same. I still think inland flooding and perhaps inland wind will be the biggest impacts; storm surge is also a threat. If Isaac does start to (finally) rapidly intensify, and end up approaching Cat. 2 status, its immediate landfall effects will be a bit more severe. But either way, this seems likely to be a serious, but non-catastrophic, hit. (The inland flooding is the one thing that still has some potential to be catastrophic, or nearly so; we’ll see.) Folks in the storm’s path should remain hunkered down, if that’s what they’ve chosen to do, and not let down their guard. But the media should also dial back the hype, as I wrote last night. This isn’t going to morph into an apocalyptic hellstorm in the final hours before the landfall. It genuinely did have that potential, but thanks to some lucky dry air entrainment, it didn’t realize its potential, despite generally near-perfect environmental conditions. So now let’s not pretend a gas station roof blowing in the wind, or some predictable storm surge in an extremely flood-prone coastal area, or inevitable widespread power outages, constitutes armageddon, mmkay?
Anyway… as I did during Irene, I thought it would be helpful to post some live tidal-gauge data here, as a sort of “one-stop shop” for tracking Isaac’s storm surge. But then I realized: why stop there? How about a one-stop shop for landfall-watching data generally? So, before we get to the tidal gauges, how about some satellite and radar maps?
Lots of images after the jump…
And now for those tidal gauges, via NOAA Tides and Currents. By way of explanation/reminder:
• The blue line is the expected, “normal” water level, as the tides come in and out. Basically, it’s what the tides would be without Isaac.
• The red line is the actual observed water level. When you see the red line not declining, or only declining slightly, while the blue line is going way down, that’s bad news. It means the storm surge is preventing the tide from going out, so the next high tide will likely be much higher (assuming the surge is still present when the tide comes in).
• The green line is the “residual” level, i.e., the difference between the red and blue lines. Basically, the green line is the storm surge. So, for instance, if the red line is declining as the tide goes out, but not as much as it “should” be declining (as in the scenario just discussed), that will cause the green line to go up.
Now, on with the show… proceeding generally from west to east along the Gulf coast…
And here are some more charts, from the St. Charles Parish Water Level Monitoring System:
UPDATE: I’ve found some more really helpful lake and river gauges from the Army Corps of Engineers. [UPDATE #2: More great stuff here!] Some of the best ones, unfortunately, I can’t figure out how to embed, but check ’em out:
And here are some more, mostly river-level gauges, which may become more important as the focus shifts from storm surge to inland flooding: