The highest temperature observed during a period (usually a day). In weather forecasts it is announced as the day's high.
今日の最高気温は35度と予報されているので熱中症に注意してください。
Today's high is forecast to be 35°C, so please watch out for heatstroke.
今年の夏は最高気温が連日30度を超えた。
This summer the daily high exceeded 30°C for consecutive days.
観測史上の最高気温が更新されたとニュースで報じられた。
The news reported that the record highest temperature was updated.