Thursday 8/23 Update

Hello everyone!  With lots of dry air still locked in over our region, it's been another big temperature swing today, going from a morning low of 58 degrees, up to a reading of 93 degrees as of the 2PM reading.  This trend should continue tonight and again tomorrow, with only small increases in humidity expected. 

Before I start in on my Isaac update, let's take care of things here at home.  Thursday is update day for the U.S. Drought Monitor, and while there wasn't much improvement, parts of the Pennyrile region of KY were dropped from "exceptional" to "extreme" drought....due to last Thursday's rain.  While this sounds like a positive development, unless Isaac can help us out (more on that later), I don't see a ton of improvement on the way anytime soon, and wouldn't be surprised if these areas get bumped back to the exceptional level soon.  If you want to check out the drought monitor, click here, and don't forget that you can click on the map to zoom into regions and states.

Our next rain chance is still set to arrive with a weak trough that will cross the region Sunday into Monday.  Out ahead of that system, there could be enough moisture for an isolated shower or storm over SEMO as early as Saturday PM, but for the rest of the area, those small isolated shower/storm chances hold off until Sunday.  Forecast models seem to be coming into agreement that the best window of opportunity for showers and storms will be Sunday night and Monday.  Here's what a couple of the models are showing:

GFS 6 hour precip ending at 1PM Monday:

European model 6 hour precip ending at 1PM Monday:

Both of these models actually bring in precip late Sunday night....Monday still looks like the best chance.  Unfortunately, totals aren't anything to get very excited about:

I'd be surprised if we average anything more that 0.25".  The threat for severe weather looks very low with this system as well.

Okay, now onto Isaac.  Hurricane hunters are continuing to fly missions into the storm to get the very latest data and fine tune the forecast.  Just for fun, here's a picture of the jet flying this afternoon's mission to launch a dropsonde (instrument packet) into the storm:

(Gulfstream IV-SP)

According to the latest advisory, Isaac is still a weak tropical storm, with maximum sustained winds at 40 mph.  However, as seen on the latest IR satellite loop, the storm seems to be organizing into a nice spiral, and is developing a nice upper outflow, a characteristic of a strengthening storm.  The key development with Isaac today has been a westward shift in the forecast track of the storm.  The GFS model, which has been wanting to steer the storm directly over Florida, or even take it east of Florida, is now trending toward the western side of the state.  Meanwhile, the European model is all over the place.  The 00Z run from last night brought the storm toward a landfall near the AL/FL border, near Pensacola:

Now, the latest run at 12Z this morning has shifted it much farther to the west, putting landfall closer to the TX/LA border:

This is an interesting development, but since this was such a big shift to the west, I think forecasters will need to see this result stay consistent for another couple of runs before thinking about buying into it.  All that said, here's the official forecast from the National Hurricane Center as of the 5PM EDT update:

Still too far out to say with a lot of confidence where this storm will eventually land, but it certainly looks like the FL panhandle could take a hit from this one.  Another question mark is how staying over the warm waters of the Gulf of Mexico would influence the intensity of the storm.  Moving over the mountainous terrain of Haiti and Cuba will weaken the storm in the near term, but once it reemerges over the Gulf from Cuba, a long trek across warm water could refuel this storm significantly. 

There are lots of story lines to go along with this storm, and many reasons to stay on top of it.  1) Over 400,000 people in Haiti are still living in tents and makeshift shelters...heavy rainfall from this storm over a largely deforested area there could lead to major flooding, landslides, and another major disaster.  2) How will this storm affect the RNC in Tampa next week?  3) Lots of folks have vacation plans along the Gulf Coast and in Florida....will you need to rethink your plans?  4) Will Isaac affect our weather locally???

If you checked out yesterday's post, you'll remember that I posted a snapshot of the European model bringing significant rains from Isaac into our region by Thursday or Friday of next week.  With the big westward shift in the model today, it also keeps the remnants well to our west.  But, the GFS model, as it inches westward, is bringing the remnants closer to our area.  Bottom line, it's still way too early to have much of a handle on where Isaac will make landfall, much less where it goes one it heads inland.  That said, a good batch of tropical rain would be a wonderful thing for our area, and is well within the realm of possibilities! We'll be watching!