Sun Aug 19 2007 05:42 PM
Re: Erin

Check out the attachment for a cool image of Erin (briefly) reborn early this morning. The attached image comes from the Norman NWS website.

I have never seen a remnant tropical system rejuvenate over land quite like Erin did last night, though I paid more attention to it than most because it happened in my backyard. It wasn't really like a typical MCS that we get around here... there was no cold pool or outflow and... well, MCSs don't have eyes either (see attached image). Erin looked better last night on radar than it ever did as a tropical storm... in fact it was probably more of a tropical storm last night (in terms of wind intensity and structure) than it ever was before (which isn't saying much).

The eye was a legitimate feature... there was intense rotation around it and it lasted for several hours, and it was the center of a vertically deep low pressure system that extended down to the surface. Just north of the eye feature, there is a Oklahoma mesonet site that reported sustained winds of 40+ mph with gusts over 60+ mph for over 3 consecutive hours (with some gusts over 70 mph) as the storm moved slowly past, from about 1-4 am CDT this morning. The winds caused extensive tree and structural damage in that area because of the duration of the event. There were numerous other strong winds reported around the path of the low as well. It also dumped 6-12 inches of rain over a large area in about a 6-hour period, resulting in catastrophic flooding in parts of the state.

The local meteorologists (both TV and NWS) were astonished by what happened last night with Erin over Oklahoma. They have seen a lot, including plenty of remnant tropical systems over the years, but nothing remotely like this. Obviously, it wasn't a purely tropical system, but it was a very close relative. As Clark mentioned, the nocturnal LLJ probably helped to crank it up, but the convection was apparently intense enough to temporarily invigorate the remnant circulation of Erin, which was still a tropical low pressure system.

Another amazing aspect of this was that the 00Z NAM from yesterday evening actually forecast something like this to happen, before anything really cranked up. It developed a small, intense low pressure system and generated outrageous QPFs (max over 10 inches) over central OK. I initially dismissed the model run because it looked like a convective feedback problem that pops up in the models sometimes, but convective feedback is something that actually happens in the atmosphere sometimes, too.

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