Deal Island, Maryland has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 10.9 °C (low) to 18.6 °C (high). Annual precipitation averages 1161.8 Millimeters. Deal Island is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -0.6 °C | 6.8 °C | 83.82 mm |
| February | 0 °C | 8.1 °C | 74.42 mm |
| March | 3.6 °C | 11.9 °C | 104.65 mm |
| April | 9.2 °C | 18.1 °C | 87.12 mm |
| May | 14.7 °C | 22.7 °C | 92.96 mm |
| June | 19.8 °C | 27.4 °C | 103.12 mm |
| July | 22.7 °C | 29.8 °C | 112.27 mm |
| August | 21.9 °C | 28.8 °C | 119.63 mm |
| September | 18.6 °C | 25.8 °C | 108.71 mm |
| October | 12.3 °C | 20.1 °C | 102.87 mm |
| November | 6.2 °C | 14.1 °C | 79.5 mm |
| December | 2.1 °C | 9.4 °C | 92.71 mm |
| Annual | 10.9 °C | 18.6 °C | 1161.78 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8a : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |