Sunny spells during baiu is called "satsukibare" (literally, sunny spells in May), but, in recent years, it is more popular that this expression is read as "gogatsubare" and means fine weather in the beginning of May by new calendar (solar calendar).
梅雨の晴れ間のことを五月晴れ（さつきばれ）というが、この言葉は最近では「ごがつばれ」とも読んで新暦5月初旬のよく晴れた天候を指すことの方が多い。