Refers to a period of unusually hot weather, often used in meteorological contexts and news reports.
A heat wave is expected to continue this week.
Electricity demand surged due to the heat wave.
熱波 is a heat wave, the direct meteorological opposite of 寒波, a cold wave.
A compound of 熱, “heat,” and 波, “wave.” The pronunciation ねっぱ reflects assimilation of the final consonant of ねつ before は.