January 30, 2026 | 06:24 am
TEMPO.CO, Jakarta - The anomalous pattern of the early 2026 rainy season is driven by several natural factors. Sonni Setiawan, a lecturer from the Department of Geophysics and Meteorology at IPB University, stated that the unique character of this rainy season, especially in Java, follows the Asian monsoon.
"However, the frequency is quite intense. This then has an impact on floods, a decrease in air temperature, strong winds, and health complaints," said Sonni in a written statement on Tuesday, January 27, 2026.
This monsoon rainfall is also reinforced by the Cross Equatorial North Surge (CENS)-the movement of cold air masses from the southern regions of China that can cross the equator and move into the Indonesian region, including Java. Apart from lowering the air temperature, CENS increases cloud formation. "This occurs due to the meeting of cold and dry air from southern China with warm and moist tropical air," he said.
When two air masses with different temperature characteristics meet, Sonni continued, there will be a process of adjustment towards thermal equilibrium. The warm and moist tropical air experiences a decrease in temperature. The water vapor inside it cools, resulting in condensation that produces more clouds. As a result, sunlight has difficulty reaching the Earth's surface, so the air between the surface and the base of the clouds is also cold.
This atmospheric phenomenon is similar to the weather conditions that triggered a major flood in Semarang on February 5-6, 2021. Based on current weather images, Java Island appears to be covered in thick clouds, with the flow of CENS from southern China to Java still active.
Sonni also raised the issue of a tropical cyclone forming in southeastern Java, which has the potential to worsen weather conditions, especially in southern East Java. "A tropical cyclone in the southeast of Java Island near Australia obstructs CENS, so more clouds are formed than usual," he said.
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