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FXUS62 KCHS 240230
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1030 PM EDT Fri Aug 23 2019

.SYNOPSIS...
Atlantic high pressure will prevail this evening, before a cold
front approaches from the north tonight. The front will cross
through the area on Saturday, then stall offshore Sunday. Low
pressure could pass well offshore during the first half of next
week. Another cold front could impact the region late next
week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
An ongoing MCS that is centered along the Central Savannah
River Area (CSRA) and covering parts of South Carolina and
Georgia, will continue to drift eastward through the post-
midnight hours. Cloud tops have been as cold as -65 to -70C and
has been sustaining itself for a few hours. This activity is
being sustained along a myriad of boundary collisions and
enhanced by deep moisture convergence, low level theta-e ridging
along with PWat in excess of 120-130% of normal. Based on
recent trends we have increased the coverage of showers and
t-storms into the scattered or numerous range near and west of
US-301, with widely scattered coverage along the northwest tier
of our South Carolina counties.

So far the heaviest rains have stayed outside the forecast
boundaries, but with weak storm motion and the deep moisture
content, we still will experience at locally heavy rainfall
where we have the highest PoPs. Flood Advisories could still be
required in a few places, with instantaneous rainfall rates as
high as 2-3 inches/hour. That doesn't mean we'll get that much
rain, but perhaps on the magnitude of 3/4 to 1 inch in an hour
or less.

After 1 or 2 am the coverage of convection will have finally
waned, where we have no more than 20-30% PoP, mainly northwest
counties.

There continues to be signals of some fog, but not enough to add
to the forecast since condensation pressure deficits aren't low
enough and there will be lingering convective debris clouds.

Lows will be about where they have been of late; lower and
middle 70s west of US-17, upper 70s to near 80F closer to the
coast.

Downtown Charleston is still on track to tie their record high
minimum temp for August 23 at 81F, set in 2014 and 2016.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Saturday: A cold front associated with a large mid/upper lvl trough
of low pressure will approach from the northwest during the day.
Ahead of the front, an onshore wind will advect deep moisture
characterized by PWATs between 2.00-2.25 inches across the region,
helping set up a round of at least scattered to numerous showers and
thunderstorms during the afternoon/evening. Modest instability
(SBCAPE 1500-1750 J/kg) should limit the overall severe weather
threat. However, an isolated strong or severe thunderstorm can not
be ruled out during the afternoon into early evening. The greater
concern will be localized heavy rainfall given deep moisture and
weak wind fields in place as the front slowly shifts into the
region. Activity should slowly weaken, but persist into overnight
hours. High temps should range in the upper 80s to lower 90s,
warmest away from the coast in Southeast Georgia. Overnight lows
should range in the low 70s inland to mid/upper 70s near the coast.

Sunday and Monday: A cold front will slowly progress to the coast
and likely stall along or just offshore Sunday, then slowly drift
further south and east into Monday. As the occurs, a potential
tropical cyclone will track north/northeast well offshore. The
position of the front and tropical entity offshore will play a
fairly significant role in how much precip can be expected across
Southeast South Carolina and Southeast Georgia early next week.
Precip chances should be highest east of the I-95 corridor on Sunday
where PWATs remain between 2.00-2.25 inches near the slowly moving
front shifting offshore. Enhanced precip chances could persist near
the coast through Monday as tropical low pressure shifts past the
area well offshore, but the overall threat of heavy rainfall should
be more limited compared to Sunday given the expected position of
the sfc front offshore and the area remaining well west of any
tropical cyclone track. Severe weather potential is quite low Sunday
and especially Monday given abundant clouds and little instability.
Afternoon highs should be a few degrees below normal, ranging in the
mid/upper 80s. Overnight lows should range around 70 well inland to
low/mid 70s near the coast.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Models are in good agreement that low pressure will be lifting
northeast away from the area Monday night into Tuesday. Another cold
front could impact the region later in the period. There are some
discrepancies in regards to convective coverage but with elevated
moisture and shortwave energy, it looks to stay a bit unsettled.
Temperatures are expected to be near normal.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Conditions are expected to be VFR a large portion of the time at
both KCHS and KSAV tonight and Saturday morning. However, there
are concerns for possible restrictions at KSAV between about
10Z and 13Z Saturday due to fog and/or stratus.

There then looks to be scattered to numerous SHRA/TSRA across
the local region Saturday afternoon and evening as a cold front
draws closer from the north. Aided by a low level flow off the
ocean and upper difluence, there is a good chance that at least
occasional flight restrictions (if not more prolonged sub-VFR
weather) will occur. For now we have just VCTS and CB clouds at
both terminals, but adjustments will definitely be required in
later TAF issuances with the potential for some heavy rainfall.

Extended Aviation Outlook: Periodic flight restrictions are possible
Saturday night/Sunday due to showers/thunderstorms associated
with a slowly passing cold front. Brief flight restrictions are
possible Monday and Tuesday behind a front stalled offshore.

&&

.MARINE...
Tonight: Tranquil weather is expected with S to SE winds at or
below 12 kt early, becoming mainly S or SW at or below 10 kt by
daybreak. Seas will be 1-3 ft.

Saturday through Wednesday: A cold front will approach from the
north/northwest Saturday and stall across the coastal waters through
early next week. Well south of the region, a tropical low should
slowly strengthen while gaining latitude off eastern Florida,
remaining beyond all coastal waters while tracking north/northeast
well off the Southeast coast. The setup will initially favor
southeast winds across coastal waters Saturday at or below 10-15 kt,
before turning predominately northeast and increasing to 15-20 kt
Sunday and Monday as the pressure gradient tightens between the
stalled front and passing tropical low offshore. Seas should also
build up to 4-5 ft. Conditions could approach Small Craft Advisory
levels for a period on Monday before the tropical low departs
north/northeast of the region Tuesday. Conditions will then remain
well below Small Craft Advisory levels through midweek.

Rip currents: Increasing east/northeast winds could contribute to an
enhanced risk of rip currents on area beaches late this weekend into
early next week, especially if tropical low pressure intensifies
while tracking well offshore.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will be running close to minor Coastal Flood
Advisory levels next week and onshore winds could lead to even
higher tides, mainly during the evening high tide cycles starting
Monday. In addition, there is the potential for some heavy rain
around the times of high tide which could exacerbate any flooding
issues.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...ETM
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...
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