Charleston boasts a year-around average temperature of 19.3°C, peaking at 27.9°C in July, its warmest month, and dipping to an average low of 9.9°C in January, the coolest. Rainfall averages at 94.0mm annually, with August seeing the heaviest showers and May being the driest month.
Month | Temperature (Celcius) | Rainfall (mm) |
| January | 9.9 | 74.7 |
| February | 11.4 | 63.8 |
| March | 14.6 | 83.8 |
| April | 18.6 | 64.3 |
| May | 22.7 | 54.9 |
| June | 26.3 | 118.1 |
| July | 27.9 | 137.2 |
| August | 27.4 | 170.4 |
| September | 24.9 | 146.3 |
| October | 20.3 | 93.2 |
| November | 15.8 | 55.6 |
| December | 11.4 | 66.0 |