The adverb of unseasonable, and in real life it is used far more often than the adjective. It sits in front of a describing word — unseasonably warm, unseasonably cold, unseasonably wet, unseasonably mild — and means 'more so than this time of year normally is'. So 'unseasonably warm' does not simply mean hot; it means hot for the date. Twenty degrees in January is unseasonably warm in Taipei; the same twenty degrees in April is just ordinary. This is standard weather-report language, and journalists like it, but it is a little formal for chatting. In ordinary talk, people say 'warm for this time of year' or just 'weird weather'. Almost every real example you meet will be about temperature or rain; you very rarely see it used for anything else.

反常地、不合時節地（多接冷、暖、多雨等天氣形容詞）。例如 unseasonably warm ＝「這個季節不該這麼暖」，重點不是「熱」，而是「跟往年同期比起來太熱」。