Monday, July 29, 2013

Hot, Isolated Rains Next Couple of Days

By Jay Grymes & Steve Caparotta

We’ve been watching spotty to isolated showers, with a few t-storms, developing along a “broken” convergence line extending from Wilkinson County southward into the coastal marshes of Terrebonne Parish.  The line hasn’t moved much, and most of the pop-up showers along the convergence zone have been short-lived, but a few have developed into stronger t-storms over lower Terrebonne.
We expect most, if not all, of the shower activity to be gone by sunset, with skies becoming mainly fair later tonight and staying that way into Tuesday morning.  We’ll open Tuesday with sunrise lows in the low 70°s for the greater BR metro area.
For Tuesday afternoon, we expect essentially a repeat of today: partly cloudy skies with afternoon rain coverage of less than 20% for the WAFB viewing area.  Highs will reach the low to mid 90°s.
Our forecast for Wednesday and Thursday are not much different either: morning lows in the low to mid 70°s, afternoon highs in the low to mid 90°s, and afternoon rain chances running at about 20%.  In the extended, we’re posting a 30% rain chance for Friday, then back down to 20% for both Saturday and Sunday.  In effect, our forecast through the work week and weekend calls for near-normal lows, slightly above-normal highs, and slightly-below-normal rain chances.

A frontal boundary to our north will not make it much farther south, keeping us under the influence of our summer-season warm-and-moist Gulf air mass.  At the mid and upper levels, ridging centered over Texas extends westward into Louisiana, serving as a weak lid on the atmosphere that limits vertical development of clouds for afternoon showers even with the “unstable” air mass in place.
Based on what we’re seeing right now, an upper-level trough will dig southward over the eastern U.S. by mid-week, putting the squeeze on the Texas ridge and nudging the ridge to the west.  That should allow for a very slight increase in rain chances for possibly Thursday and especially Friday.  But the upper trough is expected to lift out to the northeast for the weekend, allowing the Texas ridge to re-expand towards Louisiana and keeping weekend rain chances in the “isolated” category for Saturday and Sunday.
And in the tropics, the remnants of Dorian are readily apparent to the north of Puerto Rico, but the satellite imagery also shows that dry air and an upper-level low to the west of the remaining convection continue to take their toll on the remnants.  There is still no “closed low” at the surface nor does there appear to be much chance for one to develop in the near-term.  These factors -- along with the fact that some of the more trustworthy models fail to call for Dorian’s “re-birth” -- are likely to be key reasons why the NHC has dropped their re-development potential to 30% (through the next 48 hours) as of this afternoon. 

Elsewhere, there are no other Atlantic Basin tropical waves displaying any immediate threats for development at this time.

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