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000
FXUS62 KCHS 260528
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
128 AM EDT Mon Jul 26 2021

.SYNOPSIS...
High pressure will retreat northeast and weak low pressure will
approach the southeast coast tonight. The low pressure should
push onshore across southeast Georgia Monday. A persistent
trough of low pressure will then support unsettled conditions
into midweek. The trough should then weaken in favor of
building high pressure late week into next weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Upper-level winds will shift to a more zonal orientation
associated with high pressure. At the surface, sub-tropical
high pressure over the Atlantic will persist, however ridging
over the forecast area will recede as weak low pressure off the
east coast of Florida shifts northwest.

We`re seeing some of the showers associated with this low and a
coastal trough forming on the adjacent ocean waters. By early
morning, those showers that are within a region of low-level
convergence and enhanced moisture will allow for a slight
chance of showers around sunrise over the immediate coast.

Areas of low stratus will develop far inland late. If the
stratus is low enough and there could be some fog. Condensation
pressure deficits are still a bit high and it`ll be difficult to
achieve the cross-over temps, so we show just `patchy" fog after
3 or 4 AM.

Overnight temps will be a bit warmer than the previous nights,
down to 70-74F inland, with upper 70s along the barrier islands
and in downtown Charleston.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/...
Monday: Low pressure located off the southeast coast Sunday
afternoon is expected to push onshore, most likely into southeast
Georgia, Monday. This feature should inject greater moisture with
PWATs increasing to greater than 2 inches across the region, and the
chance for showers/thunderstorms should increase. Because
showers/thunderstorms associated with the offshore low remain
disorganized, maximum PoPs during maximum heating Monday afternoon
are capped at 30-40 percent south to 15-20 percent elsewhere.
However, these PoPs could prove to be conservative, especially
across southern counties. Otherwise, outside thunderstorms, expect
greater coverage of dewpoints in the 70s as compared with past
couple of days, accompanied by high temperatures in the middle/upper
80s near the coast and lower 90s inland.

Monday night: Expect a diurnal decrease in convection coverage after
dark. However, the combination of moisture and a surface trough
could continue to support isolated showers/thunderstorms south the
night, especially across southern and coastal counties.

Tuesday through Wednesday: Expect an active period with above normal
PoPs as a surface trough persists and a mid/upper upper level trough
settles into the region. Within this regime, a pool of high PWAT
values exceeding 2.25 inches, deep cyclonic flow and a series of
elongated, progressive shortwave troughs aloft should readily
support at least numerous showers/thunderstorms, with greatest
coverage during the afternoon/evening hours but also some degree of
convection persisting through Tuesday night.

This scenario could support locally excessive rainfall, and
brief/isolated episodes of damaging wind gusts cannot be ruled out
if/where mesoscale boundary/convective element interactions occur.
The latest forecasts remain quite general, and subsequent forecasts
will graduate toward greater detail regarding timing/impacts.

Outside thunderstorms, high temperatures should range from the
middle/upper 80s near the coast to the lower 90s inland. However, as
usual thunderstorms will greatly alter hourly temperatures at any
given location.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Thursday and Friday: While a surface trough will persist across the
region, medium range models continue to depict deeper moisture
shifting south of the region as the upper trough relaxes and an
inland upper ridge expands toward the east CONUS. This scenario
should support above normal temperatures and below-average PoPs
through late week. Then, the upper ridge is progged to retreat
toward the south/west, allowing the persistent NE CONUS trough to
amplify toward our region. As these subtle changes occur, a return
of moisture more typical of this time of year should translate to
normal temperatures and normal to above normal PoPs. In fact,
conditions could eventually become favorable for inland MCSs to
migrate into our region within the NW flow aloft next weekend or
beyond.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
A weak surface ridge will remain overnight, then will give way
to an inverted trough, as an area of low pressure reaches the
Southeast U.S. coast this morning. A moistening easterly low
level flow could yield a period of restrictive ceilings or fog
closer to daybreak. But this appears to be more likely further
inland from the terminals, so no mention with the latest TAFs.

The approach of the weak surface low along with much greater
moisture and modest instability will allow for scattered SHRA
and a few TSRA around the area throughout the day. Until trends
become better defined, we have just VCSH and VFR ceilings to
occur. However, brief and sporadic flight restrictions are
possible.

Extended Aviation Outlook: Low probability for brief flight
restrictions in showers/thunderstorms late Monday night. Longer
periods of flight restrictions are possible within/near more
numerous thunderstorms Tuesday through Wednesday. Then, mainly
VFR with a lowering probability for thunderstorms late week.

&&

.MARINE...
Overnight: The low pressure system to the south will draw
closer to the southeast Georgia coast late night, as the ridge
across the local waters recedes east. Provided this feature
isn`t stronger than anticipated, expect easterly winds to shift
out of the southeast with speeds 10 to 15 kt. Seas will average
2 to 4 ft.

Monday, the latest marine forecast assumes that low pressure pushing
through GA waters and onshore along the SE GA coast will remain weak
as expected. E/NE winds should veer toward the SE, mainly averaging
10-15 knots with a few gusts 15-20 knots possible. Seas will average
2-4 feet most areas except perhaps briefly up to 5 ft beyond 20
nm.

Monday night through Wednesday, outside thunderstorms S/SW winds
should average 10-15 knots and seas will average 2-4 feet, highest
beyond 20 nm. The potential for thunderstorms with locally hazardous
conditions will increase, especially Tuesday through Wednesday, and
isolated waterspouts could occur if/where mesoscale boundaries exist
of coastal waters early Wednesday.

The chance for thunderstorms should decrease after Wednesday, but SW
winds could increase and seas could build late week, especially
starting Friday. We will continue to assess the potential for SCA
conditions.

&&

.TIDES/COASTAL FLOODING...
For Monday, astronomical influences will diminish, and winds
will veer toward the southeast. Assuming low pressure pushing
onshore in SE GA remains weak as expected, there exists only a
low probability for minor salt water flooding along the
Charleston County coast with the late evening high tide.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...