Pacific seaboard; Pacific side
Refers to the side of Japan facing the Pacific Ocean, often contrasted with 日本海側 (Sea of Japan side). Used in weather forecasts, geography, and regional descriptions.
It will be sunny tomorrow on the Pacific side.
Regions on the Pacific side are relatively mild even in winter.
Refers to the Sea of Japan side, which often has heavier snowfall in winter, in contrast to the drier Pacific side.
Compound of 太平洋 (Taiheiyō, 'Pacific Ocean') + 側 (gawa, 'side').