Mermentau, Louisiana has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 58.8 °F (low) to 77.5 °F (high). Annual precipitation averages 62.9 Inches. Mermentau is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Feb. 11 - Feb. 20 through the first frost around Dec. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 41.8 °F | 60.4 °F | 6.44 in. |
| February | 45.4 °F | 64.3 °F | 4.5 in. |
| March | 51.6 °F | 71.0 °F | 3.66 in. |
| April | 58.5 °F | 77.5 °F | 5.03 in. |
| May | 66.6 °F | 84.2 °F | 5.46 in. |
| June | 72.5 °F | 89.3 °F | 6.36 in. |
| July | 74.2 °F | 90.8 °F | 5.57 in. |
| August | 73.6 °F | 91.4 °F | 6.03 in. |
| September | 69.2 °F | 87.9 °F | 5.35 in. |
| October | 58.9 °F | 80.5 °F | 4.81 in. |
| November | 49.4 °F | 70.2 °F | 4.88 in. |
| December | 43.8 °F | 62.7 °F | 4.78 in. |
| Annual | 58.8 °F | 77.5 °F | 62.87 in. |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| Average Last Frost Date | Feb. 11 - Feb. 20 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9a : 20°F to 25°F |
| Plant Hardiness Zone - 2012 | Zone 9a : 20°F to 25°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |