Under the Köppen climate classification, using the 0 °C (32 °F) coldest month (January) isotherm, New York City itself experiences a humid subtropical climate (Cfa) and is thus the northernmost major city on the North American continent with this categorization. The suburbs to the immediate north and west lie in the transition zone from a humid subtropical (Cfa) to a humid continental climate (Dfa). The area averages 234 days with at least some sunshine annually, and averages 57% of possible sunshine annually, accumulating 2,535 hours of sunshine per annum. The city falls under USDA 7b Plant Hardiness zone.