September 4, 2025
SEOUL – South Korea may see the onset of a La Nina event this fall, raising the likelihood of heavier rainfall and warmer temperatures, according to the Korea Meteorological Administration.
The World Meteorological Organization, cited by the KMA, puts the chance of La Nina forming between September and November at 55 percent, rising to 60 percent from October to December. The probabilities of neutral conditions stand at 45 percent and 40 percent, respectively.
La Nina refers to a large-scale climate pattern in which sea surface temperatures in the central and eastern parts of the Pacific Ocean fall at least 0.5 degrees Celsius below average for five consecutive months. It is the opposite phase of El Nino, which is marked by unusually warm Pacific waters.
The KMA echoed the WMO’s outlook, citing recent signs of La Nina development.
“Sea surface temperatures have recently been lower compared to average temperatures in the eastern Pacific and higher in the west,” the KMA said through an official statement issued Wednesday. “Easterly winds at around 1.5 kilometers above the western Pacific have also been recorded to be strengthening, supporting further cooling.”
The agency’s own weather forecast models put the likelihood of La Nina at 54 percent in September, rising to 68 percent in October and 57 percent in November.
If La Nina does form, Korea is likely to experience frequent and extreme weather swings.
Compared to average temperatures from previous years, Korea may see warmer-than-usual conditions in September and October, followed by colder conditions in November. This means that Korea may experience unseasonable heat this fall, while also seeing sharp cold snaps at an earlier pace than usual, going into winter.
An increased number of rainfall events may also be observed in Korea between September and October with La Nina, while drier conditions may begin to be observed from November.
As sea surface temperatures in the central tropical Pacific drop with the climate phenomenon, rainfall is reduced over the North Pacific region between September and October, promoting the development of a large-scale high-pressure circulation over the particular region. As a result, hot and humid southerly winds would be more frequently brought into Korea, triggering frequent rainfall.
However, besides the La Nina phenomenon, forecasters add that other climate factors, including the sea levels at the Arctic and sea surface temperatures in the Indian and Atlantic oceans, may cause exceptions. In recent years, these overlapping influences with the phenomenon have led to unusually warm or wet Novembers in Korea, despite a La Nina signal.
La Nina may also alter typhoon paths in early fall and accelerate the onset of cold snaps in late fall, the KMA added. If typhoon paths are altered, excessive rainfall could also occur, heightening flood hazards.
Although the probability of a La Nina occurrence has crossed the 50 percent threshold, the KMA stresses that uncertainties remain high. As fall grows nearer, the KMA plans to work with the WMO for continuous observation and analysis of the weather event.
lee.jungjoo@heraldcorp.com
