Tuesday, October 1, 2013

More Showers ... and Something in the Tropics!

As we saw on Monday, many but not all WAFB neighborhoods dealt with showers and occasional t-storms today. What was a little different today was that most of today’s rains didn’t develop in earnest until the afternoon as only the coastal parishes had morning showers.
Our Wednesday forecast calls for a near-repeat of today’s weather: a morning start around 70° for the Capital City with isolated showers -- mainly over the southern parishes. For Wednesday afternoon, plan on scattered to numerous passing showers with occasional t-storms, but not an “all day” kind of rain. We’ll call it a 50% rain chance for Wednesday with most of the “wetter” WAFB neighborhoods generally coming in at under one-half-inch of rain for the day. And much like today, Wednesday’s clouds and showers will keep highs in the mid 80°s for most WAFB communities with a handful sneaking into the upper 80°s.
The weakening stationary front draped across east Texas yesterday is gone. While it will no longer act as a driver for additional afternoon action, the air mass over the central Gulf Coast region remains very moist and unstable -- adequate fuel for afternoon rains. The moisture and heating will be further amplified by an upper-level low currently centered right over the Bayou State -- that upper low provided sufficient lift for today’s rain and it will be a player on Wednesday too. (You can easily see the upper-low in the water vapor image below, with the blue arrows indicating its counterclockwise spin.)
(You can easily see the upper-low in the water vapor image
with the blue arrows indicating its counterclockwise spin.)
As we saw yesterday, today’s afternoon rains died-down into the evening as we lost the daytime heating. Wednesday morning will again start out with partly to mostly cloudy skies, with lows around 70° or so for metro Baton Rouge and the potential for isolated showers closer to the coast but a mainly-dry commute for most of us.
I’ll go with afternoon rain chances in the “scattered” category for Thursday (around 30%) and Friday (around 30% to 40%). The modest drop-off in rain chances will allow afternoon highs to return to the upper 80°s for just about all of our viewers -- a few locations could even flirt with highs around 90°.
With a little luck, most of the rains should be over by Friday evening kick-off times for high school football.
In the extended outlook, we still have our next cold front scheduled for arrival very late on Saturday or early on Sunday. However, there remains some debate between the computer guidance as to how “healthy” the front will be. For now, I’ll split the difference, going with a 60% chance of showers and t-storms by Saturday afternoon into the evening and overnight hours with the front’s passage -- frankly, that may be a little conservative. Let’s watch how the models adjust their “thinking” for the weekend front over the next few days.
The other factor for the weekend weather is the area of disturbed tropical weather currently moving through the west-central Caribbean. “Invest 97L” still appears to be a long way from developing into a tropical cyclone (a “numbered” depression or “named” tropical storm), but the National Hurricane Center (NHC) has “upped” their potential for such development, now giving 97L a 50% chance for becoming a cyclone over the next five days. What is probably more unsettling for Louisiana residents is the shift in the early-model forecasts. Yesterday, I hinted that I expected the models to take on more northerly forecast tracks by today -- and that is just what they have done.
We now have a consensus of models bringing the system towards the central Gulf Coast, with most of the models keeping the core of the system east of Louisiana. I would not be surprised to see the consensus track shift a bit more eastward in the next day or so.
The current consensus for the Gulf Coast arrival time appears to be sometime around Saturday, ahead of the advancing cold front (noted above). In the meantime, the mid- and upper-atmosphere ahead of 97L appears to be rather dry and right now there is a fair amount of shear over the northern Gulf: both of these features -- assuming that they remain in place in some form over the next few days -- will hamper intensification. Add in the upper-level dynamics associated with the approaching weekend front and it seems as though there are a LOT of negatives working against 97L ever becoming “Karen.”
Still, we can’t rule-out a “number” (TD #12) or a weak “TS Karen” in the northern Gulf by, if not before, Saturday. In fact, given recent satellite trends, I would not be surprised to see 97L “upped” to TD #12 sometime on Wednesday.
At this stage -- with all the routine caveats in place -- Louisiana impacts are likely to be limited to some nuisance high water/modest coastal flooding along the eastern/southeastern coastline as the system approaches ... and some nervousness among those in the nearshore/offshore oil-&-gas industry.
Farther out in the open Atlantic, T.S. Jerry continues a near-stationary presence as a modest tropical storm. Jerry offers no threat to the mainland and is still expected to begin his trek towards the north, then northeast, and cooler waters in the coming days.

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