Saint Helena Island, South Carolina Weather Forecast Discussion

952
FXUS62 KCHS 252117
AFDCHS
Area Forecast Discussion
National Weather Service Charleston SC
517 PM EDT Thu Sep 25 2025
.SYNOPSIS...
A weak front will approach the region late this week, likely
stalling just offshore through the weekend. Tropical low
pressure could approach the Southeast U.S. early next week.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
A mid-level trough stretching from the Great Lakes region into
the Lower Plains this evening will shift east, becoming located
over the Northeast U.S. and stretching south into the Lower MS
Valley. At the surface, a cold front will approach from the
west. This setup will yield southwest flow, ushering moisture
into our area. PWATs could hit 2" late tonight, which is above
normal. The CAMs and the deterministic models have isolated to
maybe scattered showers across our far inland counties this
evening, with showers spreading eastwards and towards the coast
overnight. Though, the coverage should decrease overnight,
becoming more isolated. Either way, significant rainfall is not
expected. It will be another mild night with lows only dipping
into the low 70s for most of our area.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Sfc cold front edges closer to the region Friday, bringing with
it increased chances showers and storms. That being said,
should see largely dry conditions prevail throughout the morning
hours, as highs warm into the mid to upper 80s.
While the overall severe threat is expected to remain low, want
to point out the heavy rainfall could still become an issue as
PWATs near 2 inches. As noted in the previous discussion, WPC`s
latest Day 2 outlook has maintained a Marginal Risk (Level 1 of
4) of excessive rainfall for our entire area, with a Day 3
Marginal Outlook mainly highlighted across northern Berkeley
County. Though some lulls in precipitation may occur overnight,
expect showers and storms to continue through Saturday evening
as the front stalls along the coast. In regard to accumulations,
have totals ranging from 0.5 inch to 1.5 inch along and west of
I-95 - with those near the Charleston Metro ranging between
0.25 inch to 0.75 inch. However, could easily see higher totals
occur (localized pockets of 2 to 4 inches) if training storms
develop and/or storm motion is slower than anticipated.
Otherwise, expect much of the same for Sunday in terms of
showers and storms given the close proximity of the cold front
and synoptic- scale lift in the vicinity, though uncertainty
grows given 94L and TS Humberto in the western Atlantic.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
The forecast becomes exponentially uncertain into early next
week as a complicated set up begins to take shape over the
southeastern CONUS and adjacent western Atlantic waters. What we
do know is that TS Humberto has formed, and is expected to
track west-northwest over the coming days, becoming a major
hurricane by early next week. We don`t however, have great
certainty on how 94L will evolve or interact with TS Humberto.
NHC`s latest forecast now includes a 80% chance of formation
over the next 48 hours, and a 90% chance of formation over the
next 7 days. Thus, think there is enough agreement in place to
suggest that at a minimum, 94L will evolve into a TS.
Nonetheless, having two systems so close to one another
complicates matters even more, especially concerning the overall
track. While more observations (Hurricane Hunters and
additional UA soundings at WFOs) are currently being ingested
into model data, still want to point out that we will likely not
have a clear picture of what is to come at least for another
day or so. In the meantime, we encourage folks to continue
monitoring the forecast for the latest updates. Given that we
are still a few days out from any impacts, also want to
encourage folks to review their evacuation plans and emergency
kits.
&&
.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
26/00z TAF Discussion:
KCHS/KJZI/KSAV: VFR this evening. Later tonight, the forecast
becomes a bit uncertain as a number of guidance members suggest
quite a bit of stratus with some fog could approach the
terminals behind a band of weakening convection. It is unclear
how widespread these conditions will become given the number of
possible solutions noted in the data. The higher impact chances
are at KSAV where a TEMPO for MVFR cigs were introduced 09-13z.
For now, VFR were maintained at KCHS and KJZI. As for
shower/tstm chances, isolated to scattered showers could
approach the two Charleston terminals around daybreak, where
VCSH was denoted. For KSAV, a few should could approach around
midnight. The risk for showers/tstms looks to peak during the
afternoon Friday, mainly at KSAV where VCTS was depicted from
19z on. Risk looks too low at KCHS and KJZI for a mention with
this forecast cycle.
Extended Aviation Outlook: Brief flight restrictions are possible
Friday and Saturday afternoons with showers/tstorms. Otherwise,
prevailing VFR.
&&
.MARINE...
Through Tonight: A cold front will approach from the west,
especially late. This will cause S winds 10-15 kt this evening
to back to the SW overnight, then easing a few kt towards
daybreak Friday. Seas are expected to average 2-3 ft this
evening, building to 3-4 ft overnight.
Friday through Monday: Marine conditions into the weekend will
remain rather tranquil as high pressure dominates over the
marine waters. A weak front will push into the marine waters
Saturday and linger in the vicinity through the weekend and into
early next week. Through Sunday conditions are expected to
remain below Small Craft Advisory criteria, with winds generally
10 to 15 knots and seas 2 to 3 ft. The forecast becomes
significantly more uncertain late this weekend and into early
next week due to potential impacts from either 94L or TS
Humberto.
Rip Currents: The Moderate Risk of rip currents will remain at
all of our beaches through this evening.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$

NWS CHS Office Area Forecast Discussion