Tuesday, August 28, 2012

Isaac's Remnant Moisture & Us

With Isaac's gradual landfall along the northern Gulf coast tonight and early tomorrow morning, the big question is whether any of the leftover moisture from the storm impacts us and in what capacity. There are some pretty large differences between the models with regards to post-landfall track and those differences impact where the storm goes initially.

However, both the GFS and Euro do suggest that at least some of the moisture from Isaac eventually gets here. There are timing differences between the two models though. Using last night's model runs as an example, Isaac's Saturday evening position varies from either Central Missouri on the Euro to just west of Cincinnati on the GFS.  While both models take the same general path after landfall, the Euro brings Isaac north much more slowly.

As the GFS model pushes Isaac along, riding east along a bit of a frontal boundary that crosses New England, it spreads rain through Saturday afternoon into Saturday night on this particular run.  Rainfall might be a bit more substantial farther west and southwest of us (Ohio Valley) but per the GFS, Saturday  night would be our timeframe for showers and storms.

With the Euro, due to its slower movement it would take longer for the system's leftovers to impact us.  However, a second frontal boundary pushes east through the Northern Plains later in the weekend, gradually picking up Isaac's leftovers and pushing them towards our region for Labor Day night into next Tuesday.

Unlike past tropical systems that have dumped copious rainfall on the region, Isaac will not produce as prolific of a rainfall on our region if it does indeed impact our region's weather this weekend or early next week.  Isaac will have the luxury of dumping most of its heavier rainfall across the Ohio Valley and Midwest prior to impacting us so they will have higher rainfall totals and more of a flood threat than we may end up facing (if we even have to deal with flooding...that's way too early to determine since rainfall projections this far out can often change).

All that said, Isaac looks like it may impact us at some point over the Labor Day weekend -- it's just too early to say whether it's in the middle of it or the end of it.  It just won't impact all of it.