The official National Weather Service forecast for Sullivans Island — 32.7632°N, 79.8367°W, 6.7 miles from I-26. Forecasts here are written by NWS CHS, this county’s forecast office.
| Charleston County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 60 | 63 | 69 | 76 | 83 | 88 | 91 | 89 | 85 | 78 | 69 | 63 | 76 |
| Avg low °F | 39 | 42 | 48 | 54 | 63 | 70 | 73 | 73 | 68 | 57 | 47 | 42 | 56 |
| Precip in | 2.8 | 3.3 | 3.4 | 3.3 | 3.3 | 5.3 | 5.9 | 6.7 | 5.3 | 3.9 | 2.6 | 3.4 | 49.2 |
1996–2025 normals for Charleston County — the climate division Sullivans Island sits in. All-time county record high 102.9°F (1952-06-27); record low 7.0°F (1985-01-21). Source: NOAA / National Weather Service.