Hawaiian tropical dry forests are a tropical dry broadleaf forest ecoregion in the Hawaiian Islands. They cover an area of 6,600 km2 (2,500 sq mi) on the leeward side of the main islands and the summits of Niʻihau and Kahoʻolawe. These forests are either seasonal or sclerophyllous. Annual rainfall is less than 127 cm (50 in) and may be as low as 25 cm (9.8 in). The rainy season there lasts from November to March.