BMKG: Atmospheric Waves and Cyclonic Circulation Trigger Heavy Rain in May 2026
BMKG forecasts that the potential for heavy rain remains high in several parts of Indonesia during the 22-28 May 2026 period. This condition is influenced by active atmospheric wave activity and cyclonic circulation amid the transition between monsoons.
According to BMKG’s weather forecast, the recent days have shown the typical transitional weather dynamics. Daytime temperatures have felt hotter due to reduced cloud cover from morning through afternoon.
During 18-20 May 2026, maximum temperatures above 35°C were observed in several regions, including North Sumatra, Riau, Jambi, South Sumatra, Lampung, Banten, West Java, East Kalimantan, and West Kalimantan.
“Hot conditions in the morning and afternoon can support the formation of rain clouds, especially in the late afternoon to night,” BMKG said in its official statement on Saturday, 23 May.
BMKG also notes that heavy to very heavy showers are still occurring in several areas. The highest rainfall rates recorded were 133.1 mm per day in West Java, 112.8 mm per day in South Sulawesi, 105.2 mm per day in East Java, and 105 mm per day in North Sumatra. In addition, heavy rain was also observed in Jakarta, Central Papua, West Kalimantan, and Jambi.
According to BMKG, the rising rainfall potential is driven by a combination of several atmospheric phenomena, such as the Madden-Julian Oscillation (MJO) phase 4 or Maritime Continent, equatorial Rossby waves, Kelvin waves, and Mixed Rossby-Gravity (MRG).
These phenomena support the growth of rain clouds across Indonesia. On the other hand, the formation of cyclonic circulation in several areas triggers convergence zones and wind slowdowns, making the atmosphere more conducive to the development of convective clouds.
BMKG notes that the current global climate condition remains in an El Niño Condition with a Southern Oscillation Index (SOI) of -11.5 and a NINO 3.4 index of +0.68. This condition generally reduces rainfall cloud formation, especially in eastern Indonesia.
Nevertheless, intraseasonal atmospheric dynamics are still considered strong enough to sustain rainfall.
In the coming week, BMKG warns of moderate to heavy rainfall in several regions, including Aceh, West Sumatra, Riau, Jambi, Lampung, Banten, Jakarta, West Java, East Java, most of Kalimantan, Sulawesi, Maluku, and Papua.
For the period 22-24 May 2026, BMKG has issued an alert status for heavy to very heavy rainfall in Bangka Belitung Islands, Banten, Jakarta, West Java, West Kalimantan, Maluku, the Highlands of Papua, and South Papua.
Meanwhile, for 25-28 May 2026, the heavy rainfall alert could occur in West Sulawesi, South Sulawesi, and the Highlands of Papua.
BMKG also warns of the potential for strong winds in several areas, such as Aceh, North Sumatra, East Java, West Nusa Tenggara, East Nusa Tenggara, Maluku, and Papua.
The public is urged to heighten vigilance for hydrometeorological hazards, such as floods, ponding, uprooted trees, and lightning strikes.
BMKG also asks the public to regularly monitor weather information and early warnings through BMKG’s official channels to anticipate the impacts of extreme weather that can change at short notice.