Special Weather Statement, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
328 AM CDT Sun Jun 20 2021

.SYNOPSIS...

TD Claudette centered near Birmingham this morning and moving
northeast. Area of subsidence behind this system has given the
area a chance to dry out a little behind last night's deluge.
Airmass remains very moist, and dew points in the mid 70s aren't
uncommon this morning. Temperatures even at this late hour remain
mid 70s to lower 80s.

&&

.SHORT TERM (through Tuesday)...

Winds already have a southerly component, so moisture isn't going
to take long to deepen again. Precipitable water values that had
fallen to around 1.75 inches on the 00z LIX sounding are expected
to return to the 2.00-2.25 range during the afternoon hours each
day in much of the area.

Northern stream troughing will gradually push a frontal boundary
toward the area as the upper ridge over the southern Rockies
remains in place. The boundary looks to only make it about as far
south as Interstate 20, so there is really nothing to push the
moisture out of the area. As the atmosphere heats up each day,
likely to see scattered to possibly numerous showers and storms
each afternoon, possibly focused on sea breeze boundaries. Subtle
southern and northern stream shortwaves may help kick off
convection, but don't see a particular surface feature to focus
convection today, other than the frontal boundary to the north.
Current model solutions for tomorrow and Tuesday tend to favor
convective development over the Louisiana coastal parishes.
Fortunately, those areas didn't get hit too hard last night. With
the moist airmass localized heavy rain will be likely each
afternoon. Can't rule out the need for another Flash Flood Watch
at some point from tomorrow into Tuesday, but not enough
forecast confidence to justify one at this time. Don't expect any
large departures from temperature normals, outside of any early
developing convective areas.

&&

.LONG TERM (Wednesday and beyond)...

Upper ridge to our west will make several attempts to expand
toward our area, but don't see any indications of eventual success
as upper troughing over the Great Lakes reloads every 2nd or 3rd
day. May see somewhat of a diminishing trend in areal coverage of
storms beyond Wednesday, but don't see any days where we might be
able to remove the mention of thunderstorms with any confidence.
May trend temperatures a degree or two above NBM, more in line
with GFS/ECMWF operational numbers.

&&

.AVIATION (12z TAF package)...

Primarily VFR conditions at press time. May be a brief period of
MVFR to IFR conditions at KMCB around sunrise, but improvement is
expected by 15z. As noted above, diurnally enhanced convection
could start bubbling up by late morning. With no organized surface
feature, can't preclude any terminals from the VCTS mention. Of
course, if there are direct impacts, could see IFR or lower
conditions briefly. Would expect a dissipating trend toward 00z
with VFR conditions through the evening hours until at least
08-09z.

&&

.MARINE...

Will lower the Small Craft Advisory, but maintain Small Craft
Exercise Caution headlines across the coastal waters. May not see
any significant period of relaxed conditions, especially over the
open waters until Tuesday night or Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  90  73  86  72 /  40  20  70  80
BTR  90  75  86  73 /  70  30  70  80
ASD  89  75  85  74 /  60  30  70  70
MSY  90  78  86  77 /  80  30  70  70
GPT  87  75  84  75 /  70  30  70  70
PQL  87  75  85  73 /  60  30  70  70

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

Special Weather Statement
National Weather Service New Orleans LA
843 AM CDT Sun Jun 20 2021

LAZ067-068-201445-
Lower Jefferson-Lower Lafourche-
843 AM CDT Sun Jun 20 2021

...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN LAFOURCHE AND
SOUTHEASTERN JEFFERSON PARISHES...

At 843 AM CDT, a strong thunderstorm was located over Port Fourchon,
or 22 miles south of Galliano, moving east at 30 mph.

Winds in excess of 40 mph are possible with this storm.

Locations impacted include...
Grand Isle.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

If you are on or near the water, get out and move indoors or inside
a vehicle. Remember, lightning can strike out to 10 miles from the
parent thunderstorm. If you can hear thunder, you are close enough
to be struck by lightning. Move to safe shelter now! Do not be
caught on the water in a thunderstorm.

Waterspouts are possible with this storm and could possibly move
over small strips of land.

Persons in campgrounds should consider seeking sturdy shelter until
this storm passes.

LAT...LON 2914 9026 2919 9018 2915 9027 2917 9027
      2938 9004 2937 9005 2937 8999 2936 9001
      2936 8998 2931 9004 2931 8997 2930 8997
      2927 9011 2920 9008 2926 9005 2921 9007
      2929 8993 2926 8995 2909 9024
TIME...MOT...LOC 1343Z 268DEG 26KT 2914 9018

CAB