Key Model: No August Tropical Threat

For those of you who are only interested in hurricanes, tropical storms and the like, feel free to skip ahead to Long-Range Ramblings. Otherwise, the good news is that we’ll be getting more into “normal summer” mode rather than Texas BBQ mode. That means highs stopping in the low 90s and scattered afternoon showers and storms. For a few of you who would rather live in Michigan, that may be a moot point. For the rest of us, every degree matters.

Let me explain why with a different type of graphic, one that shows the moisture in the air above 10,000 feet. When the mid-level of the atmosphere is dry, shower chances are low and what rain does fall tends to be light. You often typically are quite humid on the ground with puffy cumulus overhead against a bright blue sky, but very few of those clouds can grow because they suck in dry aloft killing the updrafts. This shows today’s mid-level moisture with the browns indicating we’re bone dry.

By Thursday afternoon, a small opening in the dry air (moist air shown in blue-green) moves over South Louisiana increasing shower chances. This is the ECMWF, but all models show this lending credence to this small scale feature which should only be over us for one day.

But the big change happens late Sunday when a big slug of tropical moisture moves northward moistening the mid levels. Again, all models show this but the timing varies. Some move it in as early as Sunday morning, others hold off until Sunday night. This shows the same graphic on Monday afternoon. Notice the southerly winds aloft blowing this in.

The Foreca graphic shows the rainfall increasing, the high temperatures coming down, and the low temperatures coming up (more humid) when the slug of tropical moisture arrives late Sunday and Monday. Until then, it’s 20-30% chance of scattered mostly afternoon showers and storms. The graphic does pick up a slight tendency for more storms (40%) and slightly higher amounts on Thursday and lower chances (20%) on Saturday.

In terms of rainfall amounts, I can see a few lucky folks getting a half inch on Thursday, but most of us will be lucky to eke out a tenth of an inch or two for anything between Wednesday and Saturday. So, keep watering. On the other hand, I’m optimistic that many of us will see an inch or two anytime from Sunday-Tuesday.

REALLY GOOD NEWS! Though it’s been pretty much a given that this hurricane season would be relatively uneventful, it’s nice to see confirmation from the leading numerical prediction model, the ECMWF. This shows the chances of a tropical depression, storm, or hurricane in the critical last week of August. That’s the week of Katrina & Ida. Except for a small part of the extreme NE Gulf with a low probability, all the chances are elsewhere. The highest chances are off the Carolinas and Africa.

The current satellite image shows very few clouds in the Tropical Atlantic with the culprits being Saharan Dust over the Eastern sections and strong wind shear (high westerly winds aloft) over the Southern Gulf and Caribbean. There’s little chance of any development in the next two weeks before the time period of this graphic. Though the dust be less of a factor by late August, the shear will continue and strengthen. This might mean we’ll see a few storms eke off Africa before dying east of the Windward/Leeward islands.

Otherwise, here for Louisiana/Coastal Mississippi, I expect the rest of August to alternate between several days of above normal shower and thunderstorm chances and several days of below normal shower chances. In short…about an average August.

A better beach weekend than I had thought. The Foreca graphic for Pensacola Beach shows the same story as here. Scattered daytime showers (usually at the beach in the early AM hours, redeveloping inland during the afternoon) this week and into this weekend. More concentrated showers and storms next week. Winds won’t be a factor. With the kids in school, this could be a good time to go if the jellies can stay out to sea (sorry, I don’t forecast them - but someone probably does).