Sweeny, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 15.9 °C (low) to 26.4 °C (high). Annual precipitation averages 1283.7 Millimeters. Sweeny is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 6.8 °C | 17.7 °C | 97.79 mm |
| February | 9 °C | 19.6 °C | 67.31 mm |
| March | 12.3 °C | 22.7 °C | 80.52 mm |
| April | 15.6 °C | 25.9 °C | 89.41 mm |
| May | 19.9 °C | 29.3 °C | 113.79 mm |
| June | 23 °C | 32.3 °C | 130.56 mm |
| July | 23.7 °C | 33.2 °C | 105.66 mm |
| August | 23.6 °C | 33.9 °C | 122.43 mm |
| September | 21.4 °C | 31.8 °C | 149.35 mm |
| October | 16.5 °C | 28.2 °C | 121.41 mm |
| November | 11.4 °C | 22.9 °C | 105.66 mm |
| December | 7.8 °C | 18.9 °C | 99.82 mm |
| Annual | 15.9 °C | 26.4 °C | 1283.71 mm |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Rare |
| Plant Hardiness Zone | Zone 9b : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9a : -6.7°C to -3.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |