Friday, October 10, 2014

No Break from the Heat This Weekend

By Jay Grymes & Steve Caparotta

WAFB First Alert Quickcast:
- mornings begin with areas of fog this weekend
- staying warm & humid afternoons for Saturday and Sunday
- 20% to 30% rain chances through the weekend
- vigorous cold front arrives early next week

The forecast can just about be summed up with a single word: “ditto.”

Fog wasn’t quite as widespread nor quite as dense for most earlier this morning compared to the previous two days but we’ll keep “areas of morning fog” in the forecast through the weekend and potentially for Monday’s wake-up too.

The morning fog is the product of the moist Gulf air mass that has been sitting over us since the early part of the week and it’s not going anywhere soon.  You can expect it to persist through the weekend and right through Monday.  That not only means a morning fog potential with wake-up temperatures in the upper 60°s to low 70°s for the next three days but also warm-and-muggy afternoons with highs in the upper 80°s for most WAFB neighborhoods.  And just like we’ve seen the past couple of days, the warm-and-moist air mass will get a boost from the warmer-than-normal afternoons, producing isolated to scattered showers -- with a t-storm here and there -- over the weekend.  We’re currently setting Saturday and Sunday rain chances at about 20% to 30%: mainly the afternoon variety that track from south-to-north.

So when does autumn really return?  You’ll ‘feel’ it making a comeback on Tuesday.

If you watch the progression of weather systems with us over the coming days, you will see a cool front headed our way out of the Southern Plains on Saturday and Sunday.  That will be the first of two fronts headed our way over the next few days. The weekend front gets very close to the WAFB area but all indications are that it will stall and ‘wash-out’ before making it into our viewing area.  While we don’t expect Sunday’s front to make it into our area, it still deserves watching as it could get close enough to enhance the shower and t-storm action for us on Sunday afternoon and evening.   (For now we’ll go with rain chances at about 30% for Sunday but we may end up raising those percentages over the weekend depending on how that front behaves.)

The ‘real’ cold front that will bring back autumn will just be headed into the Central Plains on Sunday.  Based on what we are seeing now, this second cold front will be a relatively fast-mover, sweeping through the Southern Plains late Sunday and early Monday and arriving in the lower Mississippi Valley late Monday.  This will be a “Pacific” front, delivering noticeably cooler and less-humid air but not as serious a chill as we might expect from a true “Canadian” front.

We’ll need to be ready for some active weather as the Pacific front moves through.  Strong to severe t-storms appear likely across portions of the Southern U.S. as the frontal system tracks east; whether that threat will include WAFB parishes and counties is still not certain as yet -- but here’s your heads-up.  It’s looking like the primary severe weather threat will be during the overnight hours (late Monday into early Tuesday), so make sure your NOAA weather radio is ready to go.

Once that front moves through, the weather should quickly improve.  Highs on Tuesday are only expected to reach the mid 70°s for the Red Stick with skies steady clearing through the day.  And for now, at least, we’ve got morning lows in the low 50°s for metro Baton Rouge on Wednesday and Thursday with sunny skies and afternoon highs in the upper 70°s to low 80°s for most of our WAFB communities.

Now that’s more like it.

In the tropics, things are getting a little active after the run of “quiet” days that has followed mid-September’s Edouard.  Invest 99L was upgrades to Sub-Tropical Depression #7 earlier today and appears to headed towards earning the name ‘Fay’ very soon.  Note that this is currently identified as a “sub-tropical” system rather than a “tropical” system. 

Why sub-tropical?  Sub-tropical systems are sometimes defined as hybrids between fully-tropical systems and mid-latitude cyclones (our ‘winter’ storms).  For our purposes, the main difference between tropical and sub-tropical systems is that sub-tropical systems (sub-tropical depressions and sub-tropical storms) are generally a little less intense and less organized.  However, they are often larger than their tropical counterparts with the highest winds and greatest convection extending farther from the center.  In effect, sub-tropical systems tend to be less tightly-wound.  Note that in some cases, sub-tropical systems have transitioned to fully tropical configurations.  Regardless, if they get close enough to the coast, the sub-tropical variety can produce the same destructive impacts as tropical systems, including rain-generated flooding, wind damage, and storm surge.

But s-TD #7 isn’t the only feature getting attention in the Atlantic today.  The National Hurricane Center (NHC) has begun processing Invest 90L, located to the southeast of s-TD #7 and giving it a up to a 30% chance of becoming a tropical cyclone in the next five days.  In addition, there is a healthy-looking tropical wave just to the west of the Cape Verde Islands and it too may earn “invest” status in the next 24-48 hours.

All of this activity is a bit intriguing given that much of the season has been a near-dud for tropical weather enthusiasts.  But the Atlantic waters remain warm and the atmosphere has eased into a somewhat more-supportive structure over the past few days.  What’s more, while the seasonal peak of tropical activity was roughly a month ago (around September 10th), “climatology” suggests a brief secondary peak in Atlantic tropical activity during October. 

Bottom line: “it ain’t over ‘til it’s over” and the Fat Lady hasn’t started to sing just yet.  (And thankfully, we can’t think of any other over-used clich├ęs to use here!)

Have a great weekend!

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