Purpose. The study is aimed at identifying the mechanisms forming large anomalies in the water thermal conditions on the western and eastern shelf of Sakhalin Island being impacted by the atmospheric processes in spring-summer periods.

Methods and results. The data of coastal observation stations performed by the Hydrometeorological Centre of Russia in 1980–2021 permitted to study and assess the multi-year variability of water thermal regime in the fishery regions on the western and eastern Sakhalin shelf from May to August. The extreme fluctuations of monthly average thermal conditions of the water areas were revealed. The years known for formation of large negative and positive anomalies in the water thermal conditions were determined using the criterion analysis method. The fact that frequency of arising of large negative anomalies exceeds that of large positive ones was found. It was established that the mechanisms forming large anomalies were conditioned by the regional features of atmosphere circulation, i.e. by the abnormal changes in development and spreading of the atmosphere action centers (summer Far East depression, Okhotsk anticyclone and Hawaiian maximum). The cause-effect relations were determined.

Conclusions. In Sakhalin Island coastal regions, formation of large anomalies in the water thermal regime is conditioned by the abnormal changes of the baric fields structures in the regional atmosphere action centers, as well as by the changes in their local impact.