Weather Anomaly in 2025 Dry Season Baffles Indonesian Researchers

TEMPO.CO, Bandung - Climatology expert from the National Innovation Research Agency (BRIN) Erma Yulihastin said there's something different about this year's dry season in Indonesia. Several contributing factors to the dry season are less influential.

"We are confused about how to categorize this. We remain in the dark about what the real cause is," she told Tempo on Tuesday, June 17, 2025.

June and July have always been the driest months in Indonesia, Erma said, a forecast supported by tropical cyclones up north that draw clouds in the Indonesian region. Satellite data also shows that the region of Java  is relatively cloud-free, and yet, rain still pours incessantly over Jakarta and West Java, including Bandung. 

"The disappearance of the current dry season is no longer indicated by global factors located in the Pacific Ocean, such as La Niña," Erma said, adding that these factors are "no longer relevant."

Other weather-affecting factors, such as atmospheric waves, have ceased since June 6. The eastern monsoon winds that bring dry air are also considered normal. "The (monsoon wind) is now no longer the main actor of the dry season. Just merely a supporting role," said Erma.

Dry tropical cyclones have appeared about 50 times during the dry season in the last five years, starting from 2018. The vortex, which usually occurs from May to August, has also shifted. Erma mentioned that floods always appear at unexpected or "random" times throughout this year.

She suspects that the rain in mountainous areas, such as Bandung and Bogor regencies, is influenced by topographical conditions. 

"We don't fully understand the formulations for the current dry season," said Erma.

Other research shows that the wetter dry season in Indonesia is likely influenced by sea surface temperatures. Air temperature usually changes in the waters of Banda, but this time, the dynamics of the Java Sea began to also cause low-pressure systems. This, she said, potentially affects the weather for 2025 dry season. 

Dry Season Affected by Solar Activity

Researcher and Senior Expert in Astronomy Astrophysics at the BRIN Space Research Center, Tiar Dani, said that solar activity is linked to rainfall and sea surface temperatures in the long term.

"The direct impact on rainfall or sea surface temperatures is certainly much smaller compared to its indirect impact," he told Tempo on June 17.

In general, the radiation emitted by the sun will interact with the Earth's atmosphere, making it denser. "The more low-orbit satellites or debris (space junk) in orbit, the more it will re-enter Earth," said Tiar.

In a joint research with colleagues, Tiar once connected sunspots and the duration of solar radiation with rainfall and sea surface temperatures. "The results found periodicity (rainfall and sea surface temperatures) related to long-term solar activity," he said.

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