515
FXUS62 KCHS 181110
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
710 AM EDT Mon Aug 18 2025

.SYNOPSIS...
Weak high pressure will build into the region early this week
as Hurricane Erin passes well offshore through the middle of
the week. A cold front could drop into the area late this week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Aloft, the forecast area will sit in the area between
the expansive anticyclone that stretches from the Four Corners
region to the Mid Atlantic and circulation associated with Erin
over the southwest Atlantic. At the surface, the pattern will be
rather diffuse with high pressure across eastern Canada and a
slow moving front sagging across VA and into NC. Overall, the
expectation is that we will finally see a break in the near
constant diurnal convection that has impacted much of the
forecast area in the last 2+ weeks. Forcing is weak to non-
existent, and soundings off the suite of hi-res model runs
indicate very warm profiles and lower precipitable water values.
Furthermore, HREF probability-matched mean rainfall output
supports little to no diurnal convection this afternoon.
Temperatures are forecast to peak in the low to mid 90s away
from the coast, with heat index values peaking around 100.

Tonight: In the evening hours, isolated to scattered convection
could try to approach from the eastern Midlands and Pee Dee
region, perhaps bringing a bit of activity into inland portions
of Berkeley and Dorchester counties. If this occurs, it should
be on a diminishing trend and dry conditions should prevail for
the rest of the overnight. Lows are forecast to be in the low to
mid 70s.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
While situated on the eastern periphery of an mid-lvl ridge, a
drier airmass will continue to shift into the region and allow
for a less active Tuesday and Wednesday with PoPS kept at
20-30%. Expect isolated to scattered showers and thunderstorms
to initiate off the seabreeze as it pushes inland on Tuesday and
Wednesday afternoon. Simultaneously, a weak low meandering
offshore will become absorbed by Hurricane Erin as it passes
well offshore (nearly 500 miles) to the east of the region. Even
though Erin will likely remain well offshore, we will still
experience impacts from the system. A large swell associated
with Erin will likely cause a long period of dangerous surf and
rip currents through the majority of the week (see marine
section below). Heading into Thursday, mid-lvl trough swings
eastward towards the region and drops a cold front across the
region. This will shift northeasterly low-lvl flow to a more
south-southwesterly flow, and allow for a surge of moisture to
return. However, coverage remains similar to Tuesday and
Wednesday with PoPs kept at 20-30%. Highs will be near normal as
temperatures are expected to reach into the low to mid 90s.
However, lows will be slightly above normal with temperatures
only dropping into the low to mid 70s inland and then mid to
upper 70s along the coastline.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Hurricane Erin will continue to move north-northeastward across
the Atlantic and become further and further away from the
region throughout the period. This aforementioned cold front
could potentially stall across the region through the weekend. A
good amount of moisture will linger along with the front and
allow scattered to numerous showers and thunderstorms to develop
each afternoon/evening (with the highest chances on Saturday
and Sunday). Expect temperatures to remain within a few degrees
of normal.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
The 12z TAF period begins with VFR conditions at KCHS, KJZI,
and KSAV. Shallow ground fog around the terminals will be
possible for the next hour or so before dissipating. Currently,
not expecting any shower or thunderstorm activity this
afternoon and evening.

Extended Aviation Forecast: Brief flight restrictions possible
at all terminals with afternoon showers/thunderstorms.

&&

.MARINE...
Today through tonight: Winds should mostly be northeast,
turning a bit more easterly and onshore in the afternoon with
the sea breeze. Wind speeds should mostly top out in the 10-15
knot range. The main thing to watch across the local waters is
the ramping up of seas as the swell energy from Erin begins to
spread into the area. In fact, model guidance shows some
impressive swell with periods of 13+ seconds especially later
today and overnight. Seas today will mostly average 2-3 feet,
with bulk of the increase coming overnight. By late tonight,
look for 4-6 feet across the nearshore waters and 6-8 feet in
the outer waters. Small Craft Advisories are already in effect
for all the local waters outside Charleston Harbor starting
tonight.

Tuesday through Thursday: As the swell from Hurricane Erin
continues to mix into the marine zones, seas will build 6 to 8
ft across the nearshore waters (8 to 10 ft across the outer
Georgia waters). And then after, continue to build overnight on
Tuesday into Wednesday morning to 8 to 10 ft across the
nearshore waters (10 to 14 ft across the outer Georgia waters)
as Erin reaches its closest proximity by Wednesday afternoon.
This swell from Erin will be on tap throughout most of the week
and will cause a long period of dangerous surf and rip currents.
Along with the swell, north- northeasterly winds will increase
to 15 to 20 kts with gusts up 25 kts on Tuesday. As Erin draws
nearer, winds will pick up to 20 to 25 kts with gusts up to 30
kts throughout most of Wednesday.

Small Craft Advisories have been issued for all coastal waters
outside of the Charleston Harbor due to the high seas associated
with Hurricane Erin. Hazardous seas will maintain Advisories
through at least Thursday, although they will start subsiding as
Erin pulls away from the region.

Friday and Saturday: As Hurricane Erin moves north-
northeastward and pulls further away, expect the swell to slowly
back off as winds switch to east-southeasterly at 10 to 15 kts.

Rip Currents/High Surf: Model guidance suggests that swell from
Erin will begin to arrive at area beaches this afternoon.
Though guidance varies a bit, swell of up to 2 feet with periods
around 13-15 seconds should start in the afternoon and support
a Moderate Risk of rip currents at all beaches.

A period of dangerous beach conditions is expected this week as
Hurricane Erin passes well offshore to the east of the region.
Increasing long period swell will result in an enhanced risk of
rip currents at all area beaches through much of the week. A
High Risk of rip currents is forecast for Tuesday. In addition,
large breaking waves are expected, and a High Surf Advisory
could be needed towards the middle of the week.

&&

.TIDES/COASTAL FLOODING...
Increased swell and elevated winds associated with Hurricane
Erin passing well offshore could cause higher tidal levels
during the middle of the week. At least minor coastal flooding
is possible with the evening high tide cycles as early as
Tuesday. Coastal Flood Advisories could be needed.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 4 AM Tuesday to 8 PM EDT Thursday
     for AMZ350-352-354.
     Small Craft Advisory from midnight tonight to 8 AM EDT Friday
     for AMZ374.

&&

$$

NEAR TERM...BSH
SHORT TERM...Dennis
LONG TERM...Dennis
AVIATION...BSH/Dennis
MARINE...BSH/Dennis