Why Rain Falls Despite Strong El Nino, Dry Season

TEMPO.CO, Jakarta - Although the impact of the dry season is already being felt, combined with a strengthening El Nino, it does not mean that rain is entirely off the table. As was the case on July 27–29, 2026, heavy to very heavy rain was still recorded locally in several areas across Indonesia.

The Meteorology, Climatology, and Geophysics Agency (BMKG) noted that during that period, rainfall was recorded in West Sumatra (126 mm/day), the Riau Islands (97 mm/day), Aceh (83.5 mm/day), West Java (53.4 mm/day), and North Sumatra (52.6 mm/day). Daily rainfall exceeding 50 mm is classified as heavy, while levels above 100 mm are categorized as very heavy.

BMKG explained that these rains were driven by active Equatorial Kelvin Waves and Equatorial Rossby Waves moving across parts of western and central Indonesia. "Negative Outgoing Longwave Radiation (OLR) anomalies during the same window also indicated increased cloud cover that supports the formation of rain clouds across those regions," the BMKG Public Meteorology Directorate stated on July 30, 2026.

The agency added that global climate developments from July 31 to August 6, 2026, continue to favor prolonged dry conditions across Indonesia. A Nino 3.4 index reading of +2.26 degrees Celsius reflects a potent El Niño that is expected to intensify further.

This phenomenon tends to suppress rain cloud development and curtail precipitation in multiple regions. That trend is clearly visible in the forecast for early August 2026, with low rainfall expected to cover roughly 91.43 percent of the country and the remaining 8.57 percent falling into the moderate category, leaving no areas with high or very high rainfall.

Any lingering chances of rain stem from Equatorial Rossby and Kelvin Wave activity traversing parts of Sumatra and Kalimantan, which continues to nurture rain clouds. Meanwhile, spatial activity from the Madden-Julian Oscillation has the potential to influence weather patterns over eastern Indonesia.

Additionally, tropical cyclone seed 94W in the northern Pacific Ocean off West Papua is triggering wind convergence and confluence zones around the Philippine Sea and surrounding waters.

"These conditions drive the convergence and pooling of air masses, so that localized light to heavy rainfall can still occur, particularly in areas influenced by atmospheric waves, tropical cyclone seeds, and wind convergence lines," the statement concluded.

Read: Indonesia's Dry Season to Be Drier This Year, Peak in September

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