drown out

　ハワイでは、北朝鮮のミサイル発射に備えてサイレン試験が行われました。
Hawaii's attack siren barely heard on popular tourist beach

Hawaii officials were checking if sirens intended to alert tourists and residents to a possible nuclear attack from North Koreamalfunctioned or were not loud enough Friday after the first test of the warning system since the end of the Cold War was barely heard at one of the state's most popular beaches.

The sirens largely were drowned out by crashing waves and wind along Waikiki, the famous stretch of beach in the shadow of the Diamond Head volcano. Beachgoers hardly noticed the test, which sounded like a distant siren. The warning would give people 20 minutes to take shelter ahead of an imminent missile strike.

"I was out in the ocean playing around, and I heard this siren," said tourist Tom Passmore from Calgary, Canada, adding that he didn't think much of it.

http://abcnews.go.com/Politics/wireStory/attack-siren-brings-back-cold-war-era-memories-51505635

　取り上げる表現は"drown out"です。"drown"/drάʊn/ と聞くと「おぼれる」「溺死する」という意味が一番に思いつきますが、ここでは"out"と共起して別の意味で使われています。
　『ジーニアス英和辞典』第４版（大修館）で調べてみると、第３語義に「（大きな音が）（小さい音、声）をかき消す、（人の話、歌など）を（拍手など）で聞こえなくする」とありました。LDOCEでは"if a loud noise drowns out another sound, it prevents it from being heard"と定義されています。ここでは、ビーチ付近にいると、波の音にかき消されてサイレンの音が聞こえなくなるということを述べています。音が水の中に、溺れるように消えていくような様子に喩えて覚えられるかと思います。(Akim)