The Île de Batz is an island off Roscoff in Brittany, France. Administratively, it is a commune in the Finistère department of Britta…The Île de Batz is an island off Roscoff in Brittany, France. Administratively, it is a commune in the Finistère department of Brittany in north-western France. Île de Batz has an oceanic climate. The average annual temperature in Île de Batz is 12.0 °C. The average annual rainfall is 894.4 mm with December as the wettest month. The temperatures are highest on average in August, at around 17.0 °C, and lowest in February, at around 7.7 °C. The highest temperature ever recorded in Île de Batz was 35.0 °C on 18 August 1932; the coldest temperature ever recorded was −10.0 °C on 14 February 1929 and 18 December 1927.