815 FXUS62 KCHS 041817 AFDCHSArea Forecast Discussion National Weather Service Charleston SC 217 PM EDT Sat Oct 4 2025
.SYNOPSIS... Strong high pressure will extend across the region through the weekend and into early next week. A strong cold front will likely cross the area later next week.
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.NEAR TERM /THROUGH TONIGHT/... Tonight: The parent surface high across the Mid Atlantic will become aligned more east/west and centered more to the northeast of the area, allowing the low-level flow to take on a more easterly component. The result is that the coastal trough will push more to the coast and allow for shower activity to spread more inland. This is well supported by the suite of hi-res models as well as the HREF, with all showing an increasing coverage area pushing into the coast and inland around midnight and through the late night hours. There are some differences with where the peak coverage will occur, but there is general agreement with it occurring between the central Charleston County coast down to the Chatham County coast. There could be some decent rainfall amounts, generally between 0.25-0.50 inches through sunrise. Furthermore, the HREF indicates some 50% probabilities of amounts around an inch in the area between Charleston and Savannah. Will increase rain chances to account for this in the forecast. Expect another mild night with lows in the mid to upper 60s for most of the area.
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.SHORT TERM /SUNDAY THROUGH TUESDAY/... Upper level ridge holds tight across the eastern CONUS Sunday as sfc high pressure wobbles eastward across the Carolinas. An inverted trough will also continue to linger along the coast during this time, resulting in continued chances for showers and storms. As noted in the previous discussion, significant forcing with this feature remains pretty limited. Despite there being a decent push of subtropical moisture, latest CAMs continue to shift the axis of higher rainfall just south of our area. Nonetheless, still expect to see some activity here during the afternoon and evening, with the better chances for seeing showers generally along and south of Beaufort. Accumulations in these areas through Monday look to range from 0.5 to 1.5 inch, with perhaps a few isolated pockets of 2 inches.
Expect largely dry conditions to prevail Tuesday as the sfc ridge axis slides overhead. This will allow for a brief reprieve in breezy northeasterly winds - especially along the coast, with highs forecast to rise into the low to mid 80s under mostly sunny skies.
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.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... H5 heights fall modestly Wednesday as a shortwave passes north of the area, then more quickly Thursday into Friday as stronger troughing digs across the Missouri Valley and a shortwave crosses the Southeast. At the surface, strong high pressure building quickly over the Northeast will force a backdoor cold front down the eastern seaboard, likely crossing our area very early Thursday. In terms of rainfall, overall low to mid level moisture remains fairly meager, which should keep accumulations on the lighter side with any coastal shower that occurs with FROPA.
Gusty NE winds return Thursday into Friday behind the front - 25th to 75th percentile reflecting a most likely wind speed along the coast of around 20-30 mph - to end the workweek, which, in addition to already elevated tide levels, could bring a period of very impactful tidal flooding to end the week. See coastal flooding section for more.
Otherwise, model certainty decreases heading into next week, as guidance diverges on how the aforementioned front will progress. While some guidance suggest the boundary will stay outside of our area, a few solutions do have it moving back northward, causing unsettled conditions to return. Certainly something to monitor in the coming days!
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.AVIATION /18Z SATURDAY THROUGH THURSDAY/... The 18z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. VFR conditions should prevail through the evening as well. However, beginning as early as around midnight, a notable increase in shower coverage is expected to reach the coast and shift onshore. This should bring showers, reduced visibilities, and lowering ceilings into the TAF sites. This activity should generally peak in the 06-12z time period with periodic MVFR conditions with even a chance of seeing brief periods of IFR. This shower activity should shift inland and dissipate by around mid morning and VFR should return for the end of the TAF period.
Extended Aviation Forecast: The risk for restrictions from showers/tstms Sunday and Monday continues to decrease, though at least brief restrictions remain possible, especially at SAV. Otherwise, no significant aviation impacts expected.
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.MARINE... Tonight: Northeast winds will prevail early this evening, followed by a turn to become more easterly through the overnight. Wind speeds should mostly stay in the 15-20 knot range, with occasional gusts to 25 knots, especially beyond 20 nm. Seas will remain elevated with 4- 6 feet across the nearshore waters and 5-7 feet in the outer waters. Small Craft Advisories remain in effect for all local waters outside Charleston Harbor.
Sunday Onward: Very long fetch easterly winds will bring persistent medium period swell across the waters, with some underlying, but much smaller, longer period swell through early week as well. The swell will peak Sunday night into Monday with wave heights reaching 6-9 ft offshore, before only gradually subsiding through midweek, when breezy NE winds will begin to ease as well.
Rip Currents: A high risk of rip currents will continue through Monday in primarily medium period E to NE swells.
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.TIDES/COASTAL FLOODING... Tidal departures remain quite high as we move towards the early evening high tide cycle. In fact, departures continue to trend slightly higher than guidance so we have increased the forecast a tenth at both Charleston (7.5 ft MLLW) and at Fort Pulaski (9.5 ft MLLW). Therefore, the Coastal Flood Advisory is now in effect for the entire coast.
Astronomical tides will continue to increased through next week due to the upcoming full moon (Oct 7) and perigee (Oct 8). This in combination with the anticipation of continued northeasterly flow will cause the possibility of coastal flooding to become more likely along the entire coastline, including both Downtown Charleston and Fort Pulaski. Saltwater inundation could then occur during both the morning and evening high tide cycles during this time. Although there is considerable uncertainty this far out, persistent favorable winds have the potential to produce up to major coastal flooding by the latter part of next week.
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.CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117- 119-139-141. Coastal Flood Advisory from 5 PM this afternoon to 9 PM EDT this evening for GAZ117-119-139-141. SC...High Risk for Rip Currents until 8 PM EDT this evening for SCZ048>051. Coastal Flood Advisory from 5 PM this afternoon to 9 PM EDT this evening for SCZ048>051. MARINE...Small Craft Advisory until 2 PM EDT Tuesday for AMZ350-352-354. Small Craft Advisory until 6 AM EDT Wednesday for AMZ374.
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NEAR TERM...BSH SHORT TERM...SST LONG TERM...SST AVIATION...BSH/SST MARINE...BSH/SST
NWS CHS Office Area Forecast Discussion