TEMPO.CO, Jakarta - Indonesia's Meteorology, Climatology, and Geophysics Agency (BMKG) has attributed the ongoing high frequency of rainfall at the start of the dry season to several atmospheric factors.
According to BMKG, the recent occurrence of wet conditions during the dry season is not solely a result of tropical disturbances in the Indian Ocean.
BMKG’s Director of Public Meteorology, Andri Ramdhani, explained that rain clouds have been forming due to the delayed arrival of the Australian Monsoon winds and warmer sea surface temperatures surrounding Indonesian waters.
"These two factors contribute to increased air humidity and support the formation of convective clouds," he told Tempo on Friday night, May 16, 2025.
Additional contributors to the moist atmospheric conditions include Kelvin waves, Rossby waves, and the Madden-Julian Oscillation (MJO), which have further intensified rainfall over the Indonesian region.
Together, these elements have led to heightened rainfall, particularly in areas from Java to Nusa Tenggara.
BMKG also observed that the 2025 dry season could still bring above-normal rainfall across many regions. This suggests that rain may continue despite the onset of the dry season.
As of mid-May 2025, data showed that rainfall in much of southern Sumatra and Java had remained above 50 millimeters for three consecutive ten-day periods, indicating that the rainy season has yet to fully subside.
Andri also noted that BMKG has been monitoring a tropical disturbance southwest of Bengkulu since May 15. The system shows signs of cyclonic circulation and low atmospheric pressure from the surface up to the 500 hPa level.
However, no significant signs of tropical cyclone formation or intense convective activity have been detected. The system has not yet been classified as a tropical cyclone seed.
"The impact of this tropical disturbance on Indonesia's weather is indirect and not significant enough to be considered the main cause of the increased rainfall," Andri said.
Which Regions Have Entered the Dry Season?
Several seasonal zones (ZOM) in Indonesia, such as parts of Aceh and North Sumatra, have entered the early phase of the dry season. In addition, 23 ZOMs in the southern areas of Central Java and East Java have also shifted to a drier climate.
The dry season in most parts of southern Sumatra and Java is forecast to begin between May and June 2025.
Erma Yulihastin, a researcher at the Climate and Atmosphere Research Center of the National Research and Innovation Agency (BRIN), previously explained that the wet conditions during the current dry season are influenced by vortex seed dynamics in the Indian Ocean. This phenomenon continues to bring rainfall to southern Sumatra and Java.
"It is expected to persist into the second ten-day period of May 2025," she said on Thursday, May 15.
Faiz Zaki contributed to the writing of this article.
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