Weather Nerd

Isaac's Center Re-Forms; Euro Model Shifts West

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In an overnight development with major implications for both the track and intensity of Tropical Storm Isaac, the storm’s center of circulation has “relocated” underneath the ball of convection (i.e., thunderstorms) that has been blowing up all evening, previously to the north of the center.


This happens sometimes, and it means Isaac’s strengthening will likely begin in earnest now. I wouldn’t be surprised if he’s a hurricane by morning.

Meanwhile, by spontaneously “moving” 55 miles or so to the northwest of its previous position, Isaac’s center may now be on a different track trajectory, and/or may react slightly differently to the steering currents that drive the storm’s movement. The most recent set of computer model runs are less useful now, since they were based on an incorrect initial storm position, so we’ll have to see a new set of model runs to begin to understand what impact this relocation of the center will have on the track. It seems plausible that it could result in a more easterly track — perhaps increasing the risk to the Mobile area or the Panhandle, or maybe increasing the risk to New Orleans as opposed to the TX/LA border region — but we’ll need to see some model runs to be sure.

Speaking of model runs, there was also another significant development moments ago: the 00Z European model, i.e. the ECWMF or “Euro,” has shifted its landfall point from the AL/FL border region west to the LA/MS border region. It has also decreased its landfall intensity to Category 1. So this brings the Euro and the GFS more in line with one another, specifically by way of the European model joining the American model further west (U-S-A! U-S-A!). This implies the possibility of a dangerous consensus for New Orleans (ignoring the intensity issues for the moment, since that’s much harder to predict). But course, as I just said, the center relocation could throw off any such consensus, so we’ll just have to wait and see what the various 06Z models (and eventually, the 12Z Euro) show.

I’d love to stay up for the 5:00 AM EDT advisory and discussion from the NHC, but I’ve got to get to bed now — it’s 12:30 AM local (Mountain) time, I’ve gotten limited sleep all weekend due to Isaac-tracking, and I’ve got both work and my 4 1/2 year old daughter’s first day of kindergarten tomorrow. So I need to Occupy My Bed, as it were.

I’ll do my best to keep this blog updated tomorrow, and I’ll also inevitably be tweeting extensively throughout the day about Isaac.