The climate in Farmingville is warm during the summer months with temperatures in the 70s and 80s, and very cold during the winter, with temperatures as low as 30. The warmest month of the year is July with an average maximum temperature of 82.8 F, and the coldest month of the year is January with an average minimum temperature of 22.1 F. The annual average precipitation in Farmingville is 50.27 inches, with rainfall being fairly evenly distributed throughout the year. The wettest month of the year is August with an average rainfall of 4.50 inches. Snowfall is 29 inches per year. The number of days with any measurable precipitation is 107.

Temperature variations between night and day are usually fairly limited during summer with a difference of up to 18 degrees Fahrenheit, and fairly limited during winter with an average difference of 17 degrees Fahrenheit. On average, there are 206 sunny days per year in Farmingville.

Farmingville-area historical tornado activity is slightly above New York state average. It is 43% smaller than the overall U.S. average. On July 10th, 1989, a category 4 (max. wind speeds 207-260 mph) tornado 33.6 miles away from the Farmingville place center injured 40 people and caused between $50,000,000 and $500,000,000 in damages. Also on July 10th, 1989, a category 2 (max. wind speeds 113-157 mph) tornado 13.9 miles away from the Farmingville center injured one person.