leading wave; advancing wave
Specifically the initial wave of a tsunami that arrives as a crest before the trough, causing water to rush inland. Often contrasted with 引き波 (the receding wave).
See also: 引き波
The leading wave of the tsunami flooded the coastline all at once.
Understanding the mechanism of advancing and receding waves helps with disaster prevention.
Standard kanji spelling for the leading wave of a tsunami.
Variant spelling without okurigana; less common but still used in technical contexts.
Compound of 押し (oshi, 'pushing') + 波 (nami, 'wave'). The term is used in tsunami science to describe the initial surge of water.