Rock Island, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 14.8 °C (low) to 26.6 °C (high). Annual precipitation averages 1074.4 Millimeters. Rock Island is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Feb. 1 - Feb. 10 through the first frost around Dec. 11 - Dec. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 5.4 °C | 17.1 °C | 83.31 mm |
| February | 7.5 °C | 19 °C | 63.75 mm |
| March | 10.9 °C | 22.6 °C | 81.53 mm |
| April | 14.5 °C | 26.4 °C | 84.07 mm |
| May | 18.9 °C | 30.1 °C | 115.82 mm |
| June | 22.2 °C | 33 °C | 110.74 mm |
| July | 23 °C | 34.3 °C | 69.09 mm |
| August | 22.9 °C | 35.4 °C | 86.36 mm |
| September | 20.4 °C | 32.5 °C | 95.5 mm |
| October | 15.2 °C | 28.1 °C | 108.97 mm |
| November | 9.9 °C | 22.4 °C | 92.96 mm |
| December | 6.4 °C | 18.2 °C | 82.3 mm |
| Annual | 14.8 °C | 26.6 °C | 1074.4 mm |
| Average First Frost Date | Dec. 11 - Dec. 20 |
| Average Last Frost Date | Feb. 1 - Feb. 10 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |