Guide
Small craft advisories on the South Carolina coast
Checked October 8, 2026 against the National Weather Service offices in Charleston and Wilmington, North Carolina, their coastal waters forecasts, and the National Weather Service’s marine directives.
The Marine tile repeats the National Weather Service’s coastal waters forecast for the water off your town. On this coast that is the open Atlantic out twenty miles, forecast by one of two offices, plus Charleston Harbor, which has a forecast of its own. This page explains which zone each town reads, how to read the forecast, and what the advisories and warnings mean in knots and feet.
Two offices, Daufuskie Island to Little River
The weather service office in Charleston writes the coastal waters forecast for the water from the South Santee River south, which it heads “South Santee River SC to Altamaha Sound GA out 60 NM, including Charleston Harbor and Grays Reef National Marine Sanctuary”. The office in Wilmington, North Carolina, writes it from the South Santee River north, “Surf City NC to South Santee River SC out 60 NM”. Both reissue it about every six hours. The South Santee River is the line between them, and between the Charleston and Grand Strand boards.
The Lowcountry
| Zone | Name | Office | Towns on this coast |
|---|---|---|---|
| AMZ362 | Coastal waters from Edisto Beach SC to Savannah GA out 20 NM | Charleston | Daufuskie Island, Hilton Head Island, Bluffton, Port Royal, Beaufort, Lady’s Island, St. Helena Island, Fripp Island, Edisto Beach |
Charleston and its beaches
| Zone | Name | Office | Towns on this coast |
|---|---|---|---|
| AMZ340 | Charleston Harbor | Charleston | James Island, Charleston, Mount Pleasant, Sullivan’s Island |
| AMZ360 | Coastal waters from South Santee River to Edisto Beach SC out 20 NM | Charleston | Seabrook Island, Kiawah Island, Folly Beach, James Island, Charleston, Mount Pleasant, Sullivan’s Island, Isle of Palms, McClellanville |
The Grand Strand
| Zone | Name | Office | Towns on this coast |
|---|---|---|---|
| AMZ256 | Coastal waters from Murrells Inlet to South Santee River SC out 20 NM | Wilmington | Georgetown, Pawleys Island, Murrells Inlet |
| AMZ254 | Coastal waters from Little River Inlet to Murrells Inlet SC out 20 NM | Wilmington | Murrells Inlet, Garden City Beach, Surfside Beach, Myrtle Beach, North Myrtle Beach, Little River, Conway |
Murrells Inlet sits on the line between the two Grand Strand zones and reads both. Beyond the twenty-mile line are the twenty-to-sixty-mile zones, Charleston’s AMZ382 and AMZ380 and Wilmington’s AMZ284; the board reads the nearshore zones only.
Charleston Harbor has a zone; the other sounds and rivers do not
The harbour towns read Charleston Harbor first and the ocean zone outside it second. Nowhere else on this coast gets a separate forecast: not Calibogue or Port Royal Sound, St. Helena Sound, Winyah Bay, the Waccamaw or the Intracoastal Waterway. A town up a river or on the waterway, like Bluffton, Beaufort, Georgetown, Little River or Conway, reads the ocean zone off its own stretch of coast. Read it for the wind; the seas it gives are for the open water outside the inlets, and inside, the state of the water is the wind against the tide, which the forecast does not say.
Reading the forecast
Each period gives the wind by direction and speed in knots, the seas in feet, and often a Wave Detail line after them: each wave train by direction, height and period in seconds. A short period means close-set waves, steeper for their height. When zones are expected to see the same weather the office writes one paragraph headed with all their names, and when they differ, each gets its own. Charleston’s forecast also carries a water temperature line for Charleston Harbor.
What the words mean, in knots
These are the National Weather Service’s thresholds. Both offices on this coast are in the service’s Eastern Region; the warning thresholds are the same everywhere.
- Small Craft Advisory. The Eastern Region threshold is “Sustained winds or frequent gusts ranging between 25 and 33 knots” and/or seas or waves “four (4) to seven (7) feet and greater, area dependent”. The directive says the thresholds “are specific to geographic areas”.
- Gale Warning. Sustained winds or frequent gusts of 34 to 47 knots, not directly tied to a tropical cyclone.
- Storm Warning. 48 to 63 knots, likewise.
- Special Marine Warning. A short warning, usually for up to two hours, for thunderstorm winds or gusts of 34 knots or more, hail of three-quarters of an inch or more, or waterspouts.
- Tropical Storm and Hurricane Warnings. Gale and storm warnings are for wind not tied to a tropical cyclone; for a tropical storm or hurricane these are the warnings. A tropical storm warning means sustained winds of 39 to 73 mph are expected within 36 hours. A hurricane warning is issued 36 hours before tropical-storm-force winds are expected, because preparing becomes difficult once they arrive.
The line most often misread
A forecast of seas is a significant wave height: the average height of the highest third of the waves. So “seas 4 to 6 feet” is not the size of every wave; most are smaller, and some are bigger.
The weather service’s caution: wave forecasts are an average, and some individual waves “can be expected to be as much as two times greater.”
Read a forecast of six-foot seas as one that can include twelve-foot waves. And at every inlet on this coast, an ebb tide running out against an onshore wind stands the waves up at the bar; the forecast’s seas are for outside it.
Sources
- National Weather Service Charleston, marine and National Weather Service Wilmington, marine — the zones
- Charleston and Wilmington coastal waters forecasts
- National Weather Service Instruction 10-303, marine and coastal weather services — the regional Small Craft Advisory thresholds and the warnings
- National Weather Service, marine forecast FAQ — significant wave height and individual waves