507
FXUS62 KCHS 161150
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
750 AM EDT Tue Jul 16 2024

...SULTRY AND MOIST CONDITIONS CONTINUE....

.SYNOPSIS...
High pressure will persist offshore, while a weak trough
resides inland through mid week. A cold front will approach the
region late week and likely stall nearby.

&&

.NEAR TERM /THROUGH TONIGHT/...
A quick update was issued to introduce mentionable pops along
parts of the Georgia coast where KCLX is picking up on some
light shower activity.

Today: Same pattern, different day. Upper ridging centered off
the Southeast U.S coast remains in place with the Bermuda High
nudging in from the east. There some subtle changes noted in
the various moisture fields this morning, likely due to modest
convective overturning induced by scattered strong to locally
severe tstms Monday afternoon. Surface dewpoints are tad lower
compared to 24-hours ago as are both PWATs and 850 hPa theta-e
values. This will have an impact on both the level of
heat/humidity and convection this afternoon and evening.

Temperatures: RAP soundings show quite a bit of warm air in
place atop the nocturnal inversion early this morning. Once the
inversion mixes out, temperatures will rise quickly under a
solid amount of insolation. Low-level thickness schemes and 850
hPa temperatures support highs in the upper 90s well inland,
lower-mid 90s across the coastal corridor with upper 80s/near
90 at the beaches. Dewpoints will mix out across the interior
again this morning into the early afternoon before surging with
the approach of the afternoon sea breeze circulation. Dewpoints
well into the 70s will hold across the coastal counties with
readings expected to surge back into the upper 70s during peak
heating. Heat indices look to peak in the 105-108 range well
inland with 108-112 roughly along/east of the I-95 corridor.
Monday`s Excessive Heat Warning appears to have verified nicely
with a post analysis of observed heat indices from reliable
observations showing a broad swatch of heat indices 113-117
running from coastal portions of Chatham County through central
Beaufort County and along/east of US-17 in Charleston County/far
eastern Berkeley County. Given the overall lower net moisture
values expected today, any instances of heat indices 113 or
greater look to be much more isolated and generally below
warning thresholds. Per coordination with neighboring offices, a
Heat Advisory was posted for the zones along and east of the
I-95 corridor from noon until 7 PM. This included both the
Savannah and Charleston Metro Areas.

Thunderstorms: Another round of isolated to scattered airmass
driven showers/tstms is expected this afternoon/evening. 850 hPa
theta-e values are several Kelvin lower than yesterday which
will persist through peak heating. Expect isolated showers/tstms
to initiate early afternoon along parts of the inland
propagating sea breeze with convection becoming more scattered
inland as the late afternoon/evening progresses. There is a
modest signal that a weak impulse will slide northeast across
Southeast Georgia this evening as the upper ridge buckles
slightly. This may help push a more concentrated cluster of
showers/tstms east/northeast across the area south of the I-16
corridor, possibly reaching as far north as Hilton Head and
Beaufort. Pops this afternoon will range from 20% at the coast
with 30-40% inland with 20-30% along/north of I-16 and 40-50%
south of I-16 this evening. An isolated pulse severe tstm or two
will be possible, especially where updrafts are enhanced in the
vicinity of mesoscale boundary collisions. The main risk looks
to be localized damaging winds with frequent cloud-to-ground
lightning.

Tonight: Convection will gradually wind down with rain-free
conditions prevailing after midnight. It will remain warm and
humid with lows from the mid 70s well inland to the lower 80s
at the beaches and Downtown Charleston.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Ridging aloft will begin to break down on Wednesday as a broad
trough amplifies into the southeastern states. At the surface a
cold front will begin to approach the region, likely stalling in
the vicinity of the Carolinas late in the week. PWATs ahead of
the cold front will increase to over 2 inches along with
moderate to strong instability. With some synoptic forcing from
the approaching front combined with the local sea breeze,
scattered to numerous showers and thunderstorms are forecast to
develop each afternoon, with PoPs generally increasing as the
week progresses. While the threat for organized severe
thunderstorms is low, with DCAPE values forecast around 800 J/kg
a strong to marginally severe thunderstorm cannot be ruled out.

Conditions Wednesday and Thursday are expected to be hot and
humid, with slightly cooler high temperatures on Friday as the
cold front approaches. Heat Index values on Wednesday and
Thursday are forecast to reach 105-107, with some locations
reaching 108F. Heat Advisories may be required for portions of
the forecast area. However, afternoon convection may hinder
temperatures from reaching their full potential. Friday high
temperatures are forecast to reach into the low to mid 90s, with
Heat Index values of 102-105, below Heat Advisory criteria.
Overnight low temperatures will provide little relief, only
dipping into the mid 70s inland and upper 70s to around 80 along
the coast. The record high minimum temperatures could be
challenged at all three of the climate sites, see the Climate
section for more details.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Broad troughing aloft will prevail this weekend, with high
pressure extending into the forecast area from the Atlantic
early next week. At the surface, a front is forecast to linger
in the vicinity of the Carolinas through the weekend, yielding
elevated PWATs. Between lingering forcing from the nearby front
and the afternoon sea breeze circulation scattered to numerous
showers are forecast each afternoon. Guidance continues to be
rather bullish with PoPs through the long term period, so the
current forecast maintains chance to likely PoPs, still above
climatology. With above normal precipitation chances and
increased cloud cover through the period temperatures are
forecast to return to near normal, or even slightly below normal
through the weekend.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
16/12z TAF Discussion:
KCHS/KJZI/KSAV: VFR for much of the period through 17/12z. Risk
for showers/tstms will increase late afternoon into this
evening hours for KSAV as a cluster of convection moves in from
the west and southwest. A TEMPO group for MVFR conditions was
maintained, but delayed slightly to 23-01z. The main convection
axis looks to remain west of KCHS and especially KJZI, so
mention of TSRA will be included for the 06z TAF cycle.

Extended Aviation Outlook: Scattered afternoon showers/tstorms
could produce brief flight restrictions at all terminals this
week.

&&

.MARINE...
Today: Modest nocturnal surging should end prior to daybreak.
South to southwest winds will prevail today with sea breeze
enhancements likely near the land/sea interface and Charleston
Harbor as the sea breeze moves inland. Speeds will average 10-15
kt, but may be closer to 15 kt with gusts to 20 kt at the
beaches and Charleston Harbor. Seas will average 2-4 ft.

Tonight: Another modest noctural surge is expected, especially
for the South Carolina waters north of the Savannah River
Entrance. Winds will range from 15-20 kt in the South Santee-
Edisto nearshore leg to 10-15 kt with gusts to 20 kt over both
Georgia marine zones. Winds will remains somewhat tempered in
the Charleston Harbor, but should still hold in the 10-15 kt
range. Seas will average 2-4 ft.

Wednesday through Saturday: High pressure will prevail across
the marine zones while a cold front approaches the inland zones.
This will yield a slightly pinched pressure gradient between
the approaching cold front and the high pressure over the marine
waters. Overall, conditions are expected to remain below Small
Craft Advisory criteria. However, there is a chance that the
Charleston nearshore waters could see wind gusts to 25 knots on
Wednesday. Otherwise, generally S winds are forecast, 10-15
knots. Slightly stronger wind speeds are possible along the
direct coastline in association with the afternoon sea breeze.
Seas should average 3 to 4 ft.

&&

.CLIMATE...
Record High Minimum Temperatures:

July 16:
KCHS: 78/2023
KCXM: 82/2021
KSAV: 82/1883

July 17:
KCHS: 78/2023
KCXM: 82/2021
KSAV: 80/1883

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from noon today to 7 PM EDT this evening for
     GAZ116>119-138>141.
SC...Heat Advisory from noon today to 7 PM EDT this evening for
     SCZ043>045-047>052.
MARINE...None.

&&

$$