Special Marine Warning 508, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
Issued by National Weather Service Jacksonville FL
330 PM CDT Tue Aug 31 2021

...LOCALLY HEAVY RAINFALL INTO THIS EVENING SOUTHERN LA...

.SHORT TERM...Today-Friday...

A ridge of high pressure over the south central Gulf of Mexico, a
weak surface trough and ample moisture (PWATs near 2.1 inches)
will keep some chances of showers and storms going into the
evening hours and possibly overnight, with a few weak disturbances
aloft in northwest flow providing some additional support for
convection. Locally heavy rainfall expected south of I-10 into the
evening due to training bands of showers and storms. Looks like
locally heavy rain potential will fade after about 8 PM as
daytime heating ends. On Wednesday, weak surface troughing may
still exist near the coast and some drier air will be working in
from the north zones. Will keep the chance of showers and storms
mainly confined over the southern zones but anticipate chance of
showers and storms most zones. Guidance paints some likely chances
south of I-10 with spotty locations getting locally heavy
rainfall again. Wed night, a weak cold front will move in from the
north, but not quite yet moving into the forecast area, with some
low chances for showers and storms possible due to weak
convergence ahead of the boundary. Thursday, weak backdoor front
works in from the north and northeast and looks like drier air
will be filtering in. Still looks like chance of showers and
storms mainly along the Gulf coastal zones.

Hot temperatures to continue the next few days with highs in the
lower 90s. The elevated dewpoints will allow heat indices to top
100 so heat related illnesses possible. Though this is fairly
typical heat this time of year, the lack of cooling due to power
outages in our area could will lead to heat-related impacts rest
of today and again on Wednesday. A Heat Advisory remains in effect
this afternoon and again on Wednesday to highlight impacts. The
high heat indices affect more locations Wednesday. Another
advisory possible on Thursday again but dewpoints will be
dropping closer to 70/lower 70s so advisory not as likely. If
anything, highest heat indices close to 100 will be over
the southwest zones.

Friday, frontal boundary looks to shift just south of the area or
over the coastal waters, and near enough to the area to probably
support some minimal chance of convection near the coastal
zones/waters. Max temps will still be in the upper 80s and lower
90s but heat indices look to stay below 100.

.LONG TERM...Saturday-Tuesday...

Weak frontal boundary near the area will generally dissipate with
a weak pressure gradient in place and a fairly dry airmass
sticking around during the weekend. So at best right now,
isolated showers and storms mainly during the afternoon hours with
a ridge aloft keeping things a bit suppressed. A surface high
pressure system becomes more established in the Gulf of Mexico,
southeast of the forecast area, producing a south to southeast
flow. This may allow some low level Gulf moisture to stream into
the area early next week. In addition, a surface cold front is
forecast to drop southward from the Mississippi valley increasing
storm chances further Monday and Tuesday. Temps look close to
climatology with lows in the lower 70s and highs close to 90
degree.

&&

.AVIATION 18Z TAFs...

A band of showers is lingering offshore, producing scattered cloud
coverage over HUM/MSY/NEW. Skies have cleared north of this area,
which has allowed decent surface heating that will initiate
scattered showers and thunderstorms later this afternoon and
evening. Have included VCTS or TSRA at most of the TAF sites. MCB
will likely stay dry through the evening. The area will dry out
tonight and winds will become light and variable. Scattered
showers will begin to move in late in the TAF period Wednesday
morning.

&&

.MARINE...

Breezy west and southwest flow will continue rest of today. Small
craft advisory is in effect for most waters. Seas will range from
2 to 4 feet in near shore waters and about 4 to 7 well offshore.
Lingering trough will persist through Wednesday, however winds
will become lighter as remnants of Ida track further away.
Thunderstorm chances are expected in association with the trough
through at least Thursday. Generally lighter flow and seas below 5
feet expected later in the week and weekend but some low shower
and thunderstorm chances remain in the forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  89  73  92  71 /  10  10  40  10
BTR  89  73  91  72 /  20  30  50  10
ASD  90  75  92  74 /  30  20  50  20
MSY  92  78  92  77 /  40  40  50  20
GPT  89  75  91  73 /  20  20  50  30
PQL  88  73  92  72 /  30  20  40  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Heat Advisory until 5 PM CDT this afternoon for LAZ046>050-
     056>061-063>070-072-075-077-078.

     Heat Advisory from 10 AM to 5 PM CDT Wednesday for LAZ034>037-
     039-046>050-056>061-063>072-075>078.

GM...Small Craft Advisory until 8 PM CDT this evening for GMZ532-536-
     538-550-552-555-557-570-572-575-577.

MS...Heat Advisory until 5 PM CDT this afternoon for MSZ077-080>082.

     Heat Advisory from 10 AM to 5 PM CDT Wednesday for MSZ068>071-
     077-080>082.

GM...Small Craft Advisory until 8 PM CDT this evening for GMZ536-538-
     550-552-555-557-570-572-575-577.

&&