421
FXUS62 KCHS 261651
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1251 PM EDT Wed Jun 26 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while weak
cold fronts linger near our area through the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
At the surface a stationary front will meander across the SC
Upstate. Aloft a larger scale trough will be positioned over the
Great Lakes, with the forecast area in the vicinity of the
southern periphery. Temperatures this afternoon have already
reached into the low 90s across many locations, with dew point
observations in the mid to upper 70s across the coastal
counties. Further inland dew points have been able to mix out,
resulting in observations reporting in the mid to upper 60s. The
Heat Advisory is verifying already across the coastal plain,
with KJZI and KNBC reporting heat index values of 108F. No
changes were made to the areal extent of the Heat Advisory.

Ample instability will be present this afternoon across the
forecast area, however a forcing mechanism will be lacking.
Therefore, afternoon convection will be driven by the inland
pushing sea breeze and any outflow boundaries that develop.
Isolated to scattered showers and thunderstorms will be possible
this afternoon, likely dissipating by sunset. With the
instability in place, a strong to marginally severe thunderstorm
cannot be ruled out.

Tonight: Diurnally driven convection will run its course
through the evening hours. As mentioned, upper level troughiness
will edge into the southeast region through the course of the
night with enhanced QG-forcing for ascent working across the
Appalachians and into the western Carolinas. It does appear at
this juncture that any associated shower activity will remain
well upstream through the night and plan to maintain a dry
forecast. Low temperatures once again will only dip into the
middle 70s to around 80.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday: Mid-level longwave troughing initially over the East Coast
will gradually shift offshore as time progresses. More notably, a
shortwave embedded in the overall flow is expected to move over our
region during the late afternoon or evening, then stall overhead
overnight. A cold front located to our northwest at daybreak should
very slowly move into our area late in the day, likely stalling
across our area overnight. There will be a plume of deep moisture
ahead of the front. PWATs could exceed 2.25", which is above the 90%
mark for CHS per SPC Sounding Climatology. The heat will be the main
concern due to 850 mb temperatures, low-level thickness values, and
compression near the front. Highs are expected to reach the mid to
upper 90s across most of our area, except cooler at the beaches. Dew
points well into the 70s near the coast will cause heat indices to
rise to 108-110 degrees. So Heat Advisories may be needed, most
likely for our coastal counties. Forcing from the front, the
afternoon sea breeze, and the shortwave will generate convection in
the afternoon. The synoptic models and long range CAMs are in good
agreement, indicating scattered to numerous coverage. MLCAPEs should
approach 1,500 J/kg across portions of our area with some shear.
With DCAPEs exceeding 1,000 J/kg, a few marginally severe storms
with damaging winds are possible just about anywhere. Hence, the SPC
has our area under a Marginal Risk for severe thunderstorms, which
seems reasonable. Additionally, there will be the potential for
locally heavy rainfall underneath the thunderstorms due to fairly
weak steering flow and the potential for training. Convection should
gradually decrease during the evening. But isolated remnant
convection should persist everywhere overnight. Lows will be in the
70s.

Friday: The mid-levels should consist of a shortwave hovering over
our region in the morning. It is expected to dissipate into the
afternoon, followed by weak zonal flow during the evening and
overnight. At the surface, a stationary front should be spread
across our area in the morning. It`s expected quickly lift north as
a warm front into the afternoon, becoming located well north of our
area by the evening hours. Deep moisture will persist across the
region. PWATs should stay ~2.25", which is well above normal.
Similar to Thursday, high temperatures are expected to reach well
into the 90s for most areas. Dew points well into the 70s near the
coast will cause heat indices to rise as high as 108-110 degrees,
which would prompt Heat Advisories, most likely for our coastal
counties. Forcing from the remnant shortwave, departing front, and
the afternoon sea breeze will generate convection. Models point to
another round of scattered to numerous coverage, especially in the
afternoon. Instability should be similar to Thursday. However,
shear and DCAPEs appear to be lower. This would lower the severe
risk. But given the atmospheric setup and time of year, a strong or
marginally severe storm with damaging winds is possible just about
anywhere. There will also be the potential for locally heavy
rainfall underneath the thunderstorms due to weak steering flow and
the potential for training. Convection should gradually decrease
during the evening. But it`s most likely to persist closer to the
coast overnight. Lows will be in the 70s.

Saturday: Weak mid-level zonal flow will initially be over our
region, with broad High pressure building later into the day.
Surface High pressure will be in the western Atlantic, while weak
troughing develops over the Southeast U.S. later in the day. Deep
moisture will continue to prevail across the region. Similar to the
previous two days, high temperatures are expected to reach well into
the 90s for most areas. Dew points well into the 70s near the coast
will cause heat indices to rise as high as 110 degrees along the
coast. So more Heat Advisories may be needed. Instability from the
afternoon heat and humidity will generate convection along the sea
breeze as it moves inland during the afternoon. Strong or marginally
severe storms are possible.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Surface troughing or weak fronts will be impacting the Southeast
U.S. during the long term, while High pressure is located in the
western Atlantic. Expect the typical diurnal convection with the
highest POPs each afternoon and evening, then trending lower
overnight. High temperatures will be well into the 90s each day.
Additionally, heat indices could approach 108 degrees along the
coast through Monday.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
KCHS/KJZI: Scattered showers and thunderstorms are possible
this afternoon into early evening. However, indications are that
most of the activity will occur a bit inland from the
Charleston County coast and may not impact the terminals. Still
too much uncertainty to include an explicit mention in the
terminal forecasts, but will carry VCSH at KCHS during the
afternoon.

KSAV: A similar story, with showers and thunderstorms possible
this afternoon into early evening. Recent guidance trends
suggest KSAV will have the higher probabilities for showers and
storms. 18Z terminal forecast will carry VCTS at the terminal
during the mid to late afternoon period.

Extended Aviation Outlook: Mostly VFR. However, convection could
bring brief flight restrictions, mainly each afternoon and
evening.

&&

.MARINE...
Persistent southerly flow lingers across the coastal waters
through tonight, generally 10 to 15 knots with some gusts to
around 20 knots. Seas 2 to 3 feet through today building to 2 to
4 feet tonight.

Extended Marine: A typical summertime pattern is expected with High
pressure in the western Atlantic and occasional surface troughing or
fronts over the Southeast. Each day, expect gradually backing winds.
They`ll be strongest along the land/sea interface and across the
Charleston Harbor with the formation of the afternoon sea breeze.
Each night, winds will gradually veer, possibly surging closer to
the coast. Seas will be 2-3 ft.

Rip Currents: Today, increasing 1-2 foot swell energy to around
9 seconds is expected to begin impacting the South Carolina
beaches later today and into the southeast Georgia coast
tonight. With that, internal guidance suggests a moderate rip
current risk developing along the coast, particularly the South
Carolina beaches as we go through the day.

Thursday a 1-2 ft SE swell around 7 seconds and
another SE swell around 9 seconds will be impacting the beaches.
Per internal calculations, this would increase the rip current risk.
We opted to maintain a Low risk for our SC beaches, but added a
Moderate Risk at our GA beaches, where rip currents are most likely
at Tybee Beach.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 7 PM EDT this evening for GAZ101-116>119-
     138>141.
SC...Heat Advisory until 7 PM EDT this evening for SCZ043>045-
     047>052.
MARINE...None.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...