Port Isabel, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 20.3 °C (low) to 26.4 °C (high). Annual precipitation averages 659.9 Millimeters. Port Isabel is located in USDA Plant Hardiness Zone 10b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 12.4 °C | 19.6 °C | 41.66 mm |
| February | 14.1 °C | 21.3 °C | 33.53 mm |
| March | 16.9 °C | 23.3 °C | 35.81 mm |
| April | 20.2 °C | 25.8 °C | 33.78 mm |
| May | 23.4 °C | 28.7 °C | 47.75 mm |
| June | 25.5 °C | 30.8 °C | 54.86 mm |
| July | 26 °C | 31.4 °C | 38.61 mm |
| August | 26.3 °C | 31.9 °C | 42.67 mm |
| September | 25.2 °C | 30.6 °C | 149.1 mm |
| October | 22.5 °C | 28.1 °C | 82.55 mm |
| November | 17.7 °C | 24.3 °C | 54.1 mm |
| December | 13.4 °C | 20.8 °C | 45.47 mm |
| Annual | 20.3 °C | 26.4 °C | 659.89 mm |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Free |
| Plant Hardiness Zone | Zone 10b : 1.7°C to 4.4°C |
| Plant Hardiness Zone - 2012 | Zone 10a : -1.1°C to 1.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |