Wednesday, August 31, 2011

Gulf Disturbance...Anybody Got Some Darts?

I'm only half-joking here, but forecasting the future development and track of a system about to move into the Gulf is a bit like throwing darts in the dark right now.  We've got computer model solutions suggesting a landfall or near landfall anywhere from near Corpus Christi, TX to Tallahassee, FL.  Take a look at this graphic put together by Jeff Morrow showing 4 of the different possibilities:

Now, as you look at that graphic, consider that the top 2 panels (GFS and ECMWF) are models that we would generally give more weight to than the bottom 2 panels (Canadian [CMC] and Titan9 RPM).  That's not to say that the CMC and Titan9 RPM are bad models...they do fairly well with day-to-day weather...they just typically don't excel with tropical systems. So, for now, let's focus on the top 2 panels...the GFS and ECMWF ('European').

Disorganized t-storms in the NW Caribbean and southern Gulf near the Yucatan Peninsula are what could eventually give birth to a tropical system in the Gulf later this week.

The latest run of the GFS develops a weak low in the central Gulf, pushes it toward the SE Louisiana coastline, and then has it turn to the east-northeast, making landfall along the Florida panhandle. This is a big change from yesterday's run that brought a low to the LA coast then had it looping back to the south along the Texas coastline. The inconsistency from run-to-run and the fact that it's a bit of an outlier at this point leave me little reason to give it much weight at this time.

The European model develops low pressure in the western Gulf and then has it meandering there for most of next week!  Again, this is a bit difficult to buy, but I do lean more in the direction of a slow-moving system in the western or northern Gulf through the weekend and possibly even into early next week.  Because the European keeps it out over water for so long, it also produces a much stronger system by next week. Yesterday, this model kept it fairly weak.  Again, we see the inconsistency.

So by now you're probably saying, 'Just tell me where this thing is going, Steve!'  Here are my key thoughts going forward:
  • Expect little development today and tomorrow thanks to somewhat unfavorable upper-level winds. Friday looks to be the day when something may begin to happen.
  • Development will likely begin in the western Gulf.  A slow drift to the north or a meander appears most likely into the weekend.
  • High pressure that has dominated our weather this summer weakens and shifts north into the weekend. The key question becomes does this leave enough of a weakness along the western and northern Gulf coast for this system to be drawn northward?  Possibly...but that's a very difficult call at this point.
  • IF this system is left to meander in the Gulf, there will be a heavy rain threat somewhere along the Gulf Coast.  There would also likely be a sharp gradient from heavy rains along the coast to much lower totals inland.  Take a look at the 5-day rain potential from the NWS Hydrometeorological Prediction Center (HPC).

Reiterating some of my points from yesterday, there is MUCH higher than usual uncertainty both with the track and the intensity of this disturbance. I typically wouldn't put this much focus on a system that's yet to form, but with the upcoming holiday weekend and so many in the area traveling to Dallas for the football game, I want to make sure you are aware of a possible tropical threat. If you are leaving town, make sure your house is prepped just like you would for any other tropical system. Hopefully, that prep will turn out to be unnecessary, but it's the safe thing to do.
And, oh by the way, Katia looks to be on its way to becoming a hurricane later today. We're optimistic that it will move north of the Caribbean islands, but it's still too soon to completely rule out a U.S. threat.  Most of our guidance has Katia recurving well east of the U.S. East Coast, but there's still plenty of time to watch for any changes.

1 comment:

  1. Very thorough analysis! Thanks. I hope people heed your warning and take extra precautions when traveling this weekend and into next week.