Monday, July 8, 2013

Hot, Scattered T-Storms Next Few Days

By Jay Grymes & Steve Caparotta

The weekend forecast proved tougher than we had expected.  Some of you made it through both days with limited amounts of rain and no real problems, yet rain reports and radar returns showed some bull’s eyes of 3” to 4” of rain and more for a handful of locations across southern Louisiana and southwestern Mississippi.  Forecasting the “where” for those kinds of downpour pockets is impossible.

A scattered-to-numerous afternoon rain pattern returned during on Monday afternoon, fueled by a moist-and-unstable atmosphere, daytime heating and signs of a weak low spinning to the southeast over the coastal waters.  We expect the rains to back down into the evening and overnight, although spotty showers are possible overnight, especially closer to the coast.

Plan on something similar for Tuesday -- we’re going with a 40% rain chance for Tuesday afternoon and early evening.  Rain chances are expected to drop off a tad for Wednesday, but remain in the scattered category for Thursday and Friday.  Same is true for the weekend.

We’ve got to admit: the weather picture for the end of the week and the weekend is far from clear.  An upper-level trough over the U.S. and an upper-level low currently over the Bahamas will make the Thursday-through-Sunday forecast a tough one.

That upper-level low and associated tropical wave moving through the Bahamas is expected to continue moving westward and should be over the eastern Gulf later this week.  There is no impending threat for this complex to develop into a surface-based tropical system, but it does deserve monitoring.  If it makes it over the north-central Gulf, it could mean better rain chances for the weekend.  On the other hand, if it slows or stalls over the eastern Gulf -- that could mean a drier pattern for us on Thursday and/or Friday.

Then there is Tropical Storm Chantal, which earned ‘her’ name late Sunday evening.  Located over the tropical Atlantic, T.S. Chantal is just under 400 miles east of the Lesser Antilles, moving WNW at a brisk 26 mph (as of the 4PM NHC Advisory) with maximum sustained winds estimated at 45 mph.  Chantal has shown some strengthening today and the NHC anticipates some additional development over the next day or two.  On ‘her’ current track, Chantal should enter the eastern Caribbean on Tuesday and head towards the Greater Antilles during the mid-week.

For now, virtually all computer forecast models call for Chantal to slow her forward speed as ‘she’ cuts across the Greater Antilles (Puerto Rico, Hispaniola & Cuba) and then takes a more northerly track through the Bahamas into the weekend.  This scenario makes two assumptions:  (1) that interaction with the Greater Antilles weakens, but doesn’t destroy, Chantal’s surface circulation and (2) that an anticipated upper-level trough materializes over the eastern U.S. by mid- to late-week, helping to turn the system.

Given that we are talking five days out, there remains considerable uncertainly here, and we’ll be keeping an eye on this system right through the weekend.

Could things be heating-up in the tropics?  The low-latitude Atlantic “wave train” seems to be gaining some momentum.  In addition to Chantal, there is one, and possibly two, healthy waves marching behind ‘her’ from east-to-west.  Neither offers any immediate threat for development, but both will bear watching in the coming days.

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