Special Marine Warning 480, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
624 PM CDT Mon Aug 23 2021

.AVIATION...
Some terminals will experience brief ceiling drops as well as
some gusty winds as showers and thunderstorms move through the
area. Once convection clears terminals should return to VFR
conditions. /TDB/

&&

.PREV DISCUSSION... /issued 327 PM CDT Mon Aug 23 2021/

SHORT TERM...
Tonight through Wednesday...
A weak backdoor trough is expected to linger over the area for the
next few days. Upper level ridging is expected to weaken slightly
over the next few days. Southerly surface winds will help to
advect warm air and moisture into the region, which will help
enhance lifting and humidity in the environment. PW values will be
relatively low over the next couple of days, especially Tuesday,
with values ranging from 1.7 to 2.0, which is below the 75th
percentile for the SPC sounding climatology. As a result, any rain
that occurs will not be very efficient and will not produce as
high of rainfall rates. Isolated to scattered showers and storms
will be possible over the next few days, looking at the models,
primarily during the peak daytime heating hours. The main threats
from these storms will be gusty winds (30-40mph) and frequent
lightning. Locally heavy rainfall may be possible inside
thunderstorm development Wednesday afternoon.

Since Tuesday is expected to be fairly dry overall based on model
consensus while still maintaining abundant humidity and higher-
than-normal temperatures, there will also be the concern for heat.
Heat index values are forecast to be between 108 and 112 for most
of the area tomorrow, and rainfall will not be abundant enough to
provide relief tomorrow. As a result, a heat advisory has been
issued much of the area tomorrow with the main timeframe for the
highest risk of heat stress and heat illness occurring from 9AM to
7PM CT. Staying hydrated tomorrow will be critical to preventing
heat illness and stress. Heat does not look like it will be as
much of a concern on Wednesday. Rainfall coverage will be higher
and more numerous in nature, which will help to provide relief
from those high heat index values. MSW

LONG TERM...
Thursday through Sunday...
Thursday through Sunday, normal summertime pattern and upper
level ridging will dominate the area. Deep tropical moisture will
be abundant in the Gulf of Mexico toward the end of the week,
looking at the models. Southerly to easterly surface winds will
help to advect warm air and deep tropical moisture into the
region. Scattered to numerous showers and storms will be possible
as we move toward the end of the week and the weekend. These
showers and storms will be increased in coverage more than normal
due to the abundant moisture presence in the atmosphere. Looking
at the models, PW values will be around 2.1 to 2.2, which is above
the 75th percentile for the SPC sounding climatology, especially
during the daytime hours Thursday through Sunday. As a result,
rainfall will be more efficient with higher rainfall rates (1-3
inches) each of these days. Model consensus is indicating that
there will still be plenty of moisture toward the end of the week
during the overnight hours as well. So, it is likely we could see
scattered showers and storms during the overnight hours these days
with numerous showers and storms likely during the peak daytime
heating hours. The main threats from these storms will be locally
heavy rainfall inside of thunderstorm development. Gusty winds
(35- 45mph) and frequent lightning will be possible, as well.

Additional features of note in the long-term forecast is the fact
that the models are trying to produce some tropical disturbances
in the Gulf of Mexico toward the weekend. However, model consensus
is very uncertain and there are many differences in the models on
timing, strength, and location of these potential disturbances.
This is something that we will be monitoring in the next few days
closely, but likely the main impact from any development, looking
at the current models, toward the end of the week would be
increased rainfall chances at this point. Regardless, we are
steadily approaching the peak of hurricane season, so it is always
a good idea to update your hurricane plans and check your
supplies. MSW

AVIATION...
18Z TAF Package...
VFR conditions prevail at all area airports and will persist
through the forecast period. Vicinity isolated showers will be
possible this afternoon at most area airports (not BTR or MCB),
which could cause lower ceilings and visibilities temporarily.
Winds shifts greater than 30 degrees will also be possible at most
area airports throughout the forecast period, especially at MSY,
NEW, HUM, and GPT. MSW

MARINE...
Tonight through Thursday, winds will be southerly and moderate
(<15 knots). Friday through Monday, winds will be easterly and
moderate (<15 knots). Wave heights will correspond to the wind
speeds. MSW

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  75  95  74  94 /  10  20   0  70
BTR  76  95  75  93 /  10  40  10  80
ASD  77  96  76  93 /  30  40  30  90
MSY  81  96  81  94 /  20  30  30  90
GPT  77  93  77  91 /  10  20  30  80
PQL  75  94  75  91 /  10  30  40  80

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Heat Advisory until 7 PM CDT this evening for LAZ034>037-039-
     046>050-056>061-063>065-071-072-075>078.

     Heat Advisory from 9 AM to 7 PM CDT Tuesday for LAZ034>037-039-
     046>050-056>061-063>065-071-072-075>078.

GM...None.
MS...Heat Advisory until 7 PM CDT this evening for MSZ068>071-077-
     080>082.

     Heat Advisory from 9 AM to 7 PM CDT Tuesday for MSZ068>071-077-
     080>082.

GM...None.
&&

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