According to the weather agency, there is a 60 percent chance that temperatures in June and July will be higher than the seasonal average. For August, the peak summer period, the probability is estimated at 50 percent.
An analysis by the World Meteorological Organization, using 525 climate model datasets from meteorological agencies and institutions in some 12 countries, also points to a warmer-than-usual summer for South Korea. The analysis put the probability at up to 76 percent that temperatures from June to August would exceed seasonal norms.
These forecasts are attributed to unusually warm sea surface temperatures in the North Indian Ocean and North Pacific. Warmer waters in the North Indian Ocean can strengthen convective activity and help generate atmospheric wave patterns that favor high-pressure circulation east of South Korea.
Such high pressure systems can draw hot and humid southerly winds toward the peninsula. In recent summers, a strong North Pacific high parked southeast of South Korea has repeatedly helped produce extended periods of oppressive heat.
The KMA also cited the likely persistence of a positive North Atlantic tripole pattern, which can help build high pressure in the upper atmosphere over South Korea. That pattern tends to increase sunshine and suppress cloud formation, raising temperatures further.
El Niño is another factor. Sea surface temperatures in the central and eastern tropical Pacific are expected to rise through the June-August period, increasing the chance of El Niño conditions. U.S. and international forecasters have said the event could strengthen toward a "super El Niño" level by autumn.
Waters around South Korea are also already warmer than usual and are expected to remain so through the summer. The KMA said the probability of above-normal sea surface temperatures was especially high in the East Sea, reaching 70 percent in June and July.
Warmer seas can increase the supply of water vapor to the atmosphere, intensifying both heat and the risk of extreme rainfall. The KMA said stronger-than-usual warm currents, including the Tsushima Warm Current and the East Korea Warm Current, have raised ocean heat content near the peninsula.
The forecast follows a string of record-breaking warm seasons. Over the past 53 years, South Korea's average June temperature has risen by 1.7 degrees Celsius, while July and August temperatures have climbed by 1.3 degrees and 1.4 degrees, respectively.
This year's monsoon season is expected to bring similar or slightly higher levels of rainfall in June and July. The likelihood of heavy rain is linked to hot, humid air flowing into the inland areas from the south.
Meanwhile, the Korea Disease Control and Prevention Agency said it began operating shelters and facilities to respond to heat-related illnesses and emergencies last week, and will continue to run them until the end of September in cooperation with more than 500 medical institutions across the country.
Heat-related illnesses including heatstroke can cause symptoms such as headaches, dizziness, muscle cramps, fatigue and loss of consciousness, and can be fatal if left untreated.
The number of reported heat-related illness cases rose to 4,460 last year, up more than 20 percent from 3,704 a year earlier, and close to the 4,526 cases recorded in 2018, when South Korea experienced its longest-ever stretch of extreme heat days.
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