Thursday, August 21, 2014

Hot August Weekend Ahead!

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:

- heat continues for Friday & the weekend
- rain chances drop to less than 20% over the next three days
- lots of interest in the tropics

For the second day in a row, afternoon thunderstorms were more widespread than anticipated. The upper-level ridge that we’ve been talking about for days remains in play, but a small, mid-level low has been working with our warm-and-unstable Gulf air and sea-breeze set-ups to produce some afternoon fireworks. As before, the action winds down as the sea-breeze departs and the daytime heating fades. We’ll go to fair to partly cloudy skies overnight and into Friday morning with sunrise lows in the mid 70°s for metro Baton Rouge.

And like yesterday, while the storms and clouds provided some heat relief, Metro Airport (BTR) still managed to hit 95° before the weather produced a marked temperature drop. That also makes three days in a row with highs of 95° for BTR -- that’s the three hottest consecutive days for BTR since early July of 2012.

Can we expect another round of scattered t-storms for Friday afternoon? Given the coverage of storms for yesterday and today, we won’t rule it out, but we do believe that the mid-level low that generated today’s action will be just about gone -- we’ll call for isolated t-storms and rain chances at 20% or less for Friday afternoon.

We’ve got it even “drier” for Saturday and Sunday, calling for spotty rains at best on both days. But what we can expect is even more heat for Friday and the weekend, with highs in the mid to upper 90°s for just about everyone for all three days.

Heading into next week, the upper-level ridge will begin to relax a bit, allowing for more clouds, better rain chances and a drop back into the low 90°s for highs.

So what about the tropics, specifically Invest 96L? A hurricane hunter aircraft found winds of tropical-storm force in the vicinity of the tropical low, but the structure of the disturbance - - including a lack of convection (thunderstorms) near the estimated area for the surface low - - is too ragged for an upgrade to tropical depression status. However, the National Hurricane Center does give 96L a 50% chance for that upgrade over the next two days and a 70% chance over the next five days. 

This is not a time to drop your guard or stop those early preparations, and it is still too early to make definitive claims about the ultimate path that this tropical system will take. However, most of the latest computer analyses suggest that this system will remain in the Atlantic, regardless of its intensity in the coming days.

By the way, what is an “Invest” anyway? The term "Invest" is assigned to a tropical wave/disturbance (an area of disturbed weather, a cluster of thunderstorms) that is thought to have some potential for development into a tropical cyclone (a tropical depression or stronger). The term is shorthand for “investigation (investigative) area.”

In the Atlantic Basin, tagging a disturbance as an Invest signals that the National Hurricane Center is formally monitoring the area and is ready to begin the collection and evaluation of meteorological data associated with the disturbed area, as well as initiate the running of computer models on it. The Invest designation also alerts cooperating agencies (government and academic groups) to begin data processing in earnest.

Officially, designation as an Invest does not mean that the tropical disturbance has an increased likelihood for development, but it is a clear sign by the NHC experts that they think the area has at least some potential.

Invests are numbered from 90 to 99, and labeled with an “L” for disturbances in the Atlantic Basin. (By comparison, an “E” is used for Invests in the eastern Pacific). Given this naming scheme for Invests, you can see that during an ‘active' year, there could be two or more “90L” Invests before the season ends. Keep in mind that over the course of a tropical season, we could see as many as 50 to 70 (or more) tropical waves over the Atlantic, although only a small proportion of those earn Invest designation.

Take this season for example: we are currently watching 96L, the sixth Invest of the season. Yet only three have become tropical cyclones: hurricanes Arthur & Bertha, and between them, Tropical Depression #2.

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