Hercules, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 9.8 °C (low) to 20.2 °C (high). Annual precipitation averages 496.8 Millimeters. Hercules is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 5.8 °C | 13.3 °C | 96.01 mm |
| February | 6.6 °C | 15.6 °C | 104.39 mm |
| March | 7.8 °C | 17.8 °C | 67.56 mm |
| April | 8.9 °C | 19.6 °C | 33.02 mm |
| May | 10.8 °C | 21.7 °C | 15.49 mm |
| June | 12.4 °C | 23.9 °C | 4.06 mm |
| July | 13.4 °C | 25.1 °C | 0 mm |
| August | 13.6 °C | 25.1 °C | 1.02 mm |
| September | 13.1 °C | 25.4 °C | 1.78 mm |
| October | 11.3 °C | 23 °C | 21.34 mm |
| November | 8.1 °C | 17.8 °C | 51.31 mm |
| December | 5.8 °C | 13.6 °C | 100.84 mm |
| Annual | 9.8 °C | 20.2 °C | 496.82 mm |
| Average First Frost Date | No Frost |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 9b : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9b : -3.9°C to -1.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |