San Juan, Texas has a Hot Semi-Arid Climate climate (Köppen classification: BSh). Average annual temperatures range from 18 °C (low) to 29.8 °C (high). Annual precipitation averages 565.2 Millimeters. San Juan is located in USDA Plant Hardiness Zone 10a.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 9.7 °C | 21.7 °C | 21.08 mm |
| February | 11.9 °C | 24.2 °C | 25.15 mm |
| March | 15.1 °C | 27.1 °C | 29.72 mm |
| April | 18.3 °C | 30.2 °C | 35.05 mm |
| May | 21.8 °C | 32.8 °C | 58.17 mm |
| June | 24 °C | 35.2 °C | 63.5 mm |
| July | 24.6 °C | 35.9 °C | 57.4 mm |
| August | 24.6 °C | 36.6 °C | 40.64 mm |
| September | 22.8 °C | 33.7 °C | 120.4 mm |
| October | 18.8 °C | 30.9 °C | 59.69 mm |
| November | 14.2 °C | 26.3 °C | 31.75 mm |
| December | 10.5 °C | 22.4 °C | 22.61 mm |
| Annual | 18 °C | 29.8 °C | 565.16 mm |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 10a : -1.1°C to 1.7°C |
| Plant Hardiness Zone - 2012 | Zone 9b : -3.9°C to -1.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | BSh - Hot Semi-Arid Climate |