An analysis by the state weather agency found that the accelerating sea surface temperature in the North Pacific Ocean was a main cause of consecutive heat waves and heavy rainfall events this summer.

The Korea Meteorological Administration(KMA) reported on Thursday that the national average temperature this summer was 25-point-seven degrees Celsius, up from last year's 25-point-six degrees and the highest on record since 1973.

The average daytime high was 30-point-seven degrees, setting another fresh record, while the average morning low was 21-point-five degrees, the second highest in the books.

There were 28-point-one heat wave days, the third highest on record, and 15-point-five tropical nights.

The average surface temperature of seas surrounding the country stood at 23-point-eight degrees, the second highest over the 2016-2025 period, with 24 degrees in 2024 topping the list.

This year's heat wave started in late June, with daily average temperatures hitting new records nearly every day from June 29 to July 10.

Meanwhile, the earliest onset of tropical nights came on June 19 in Daejeon and Daegu.

The KMA said the early heat wave following a shorter period of monsoon rains was largely due to high sea surface temperatures which caused a high pressure system from the North Pacific to expand to the southern regions in late June, much earlier than normal.

Despite experiencing the second-shortest monsoon season, which ended on July 1, the country received a total of 619-point-seven millimeters of precipitation, or 85-point-one percent of the yearly average, with the number of rainy days hitting 29-point-three, up nine-point-two days from the average.

After the monsoon period, there were still extreme downpours with up to 700 millimeters of rainfall recorded nationwide between July 16 and 20, after a low pressure trough accompanied by cold air got trapped in the upper layers of the atmosphere by the high pressure system creating unsettled weather.