South Korea is experiencing a simultaneous surge in extreme heat and heavy rainfall across Jeju Island and the southern coastal regions this week [1, 2].

This weather pattern signals an abrupt seasonal transition that threatens to disrupt daily travel and infrastructure. The combination of a high-pressure ridge and the onset of the monsoon season creates volatile conditions for residents and visitors in the south [3, 4].

Heavy rain began on the morning of June 1, 2026, on Jeju Island [2]. A meteorology reporter said the downpours are expected to spread to the south-coast on Tuesday [2].

While the south faces flooding risks, the northern regions are battling intense heat. The Korea Meteorological Administration said temperatures are expected to reach 33 °C in Seoul tomorrow, which is well above the seasonal average [1].

This dual weather phenomenon is driven by the simultaneous arrival of summer heat and the rainy season. A travel guide author said June marks this period on Jeju, bringing a mix of sunshine and frequent showers [3]. The heat is further intensified by a high-pressure ridge driving temperatures above the norm [4].

Local authorities are monitoring the southern coast as the rain moves inland on Tuesday [2]. The rapid shift from high heat to torrential rain often complicates emergency preparedness and urban drainage management in coastal cities [2, 4].

“Temperatures are expected to reach 33 °C in Seoul tomorrow, well above the seasonal average.”

The convergence of an early heatwave and monsoon-level precipitation suggests a volatile start to the 2026 summer season. When high-pressure ridges coincide with the rainy season's onset, it often results in more intense atmospheric instability, increasing the risk of flash floods in coastal areas and heat-related health emergencies in urban centers like Seoul.