Dry Season Already Hits Indonesia, Why Does BMKG Warn of Heavy Rain?
The Meteorology, Climatology, and Geophysics Agency (BMKG) has issued an extreme weather warning to the Indonesian public, particularly in several regions of Sumatra and Java over the next week. BMKG’s analysis indicates that, although Indonesia has entered the dry season period, the potential for heavy rain and strong winds remains high.
Previously, BMKG recorded that by the end of March 2026, 7% of Indonesia’s Monsoon Zones (ZOM) had entered the dry season. This figure is expected to increase significantly. BMKG forecasts that most of Indonesia will begin entering the dry season in April, May, and June 2026.
During the period of 2-5 April 2026, BMKG noted that several areas in Indonesia experienced heavy-intensity rain. This means the potential for extreme rain still exists in various parts of Indonesia. It is explained that this condition is influenced by the continued activity of atmospheric waves such as the Equatorial Rossby, Kelvin, and Mixed Rossby-Gravity (MRG) waves in some areas, as well as the Madden-Julian Oscillation (MJO) phenomenon crossing much of Sumatra. Additionally, the transition period from the Asian Monsoon to the Australian Monsoon also shapes the air circulation patterns and convergence zones in several regions.
Other factors, such as slowing winds and strong daytime surface heating, further support the growth of convective clouds that could cause rain. On the other hand, BMKG is monitoring cyclonic circulations in the waters southwest of Aceh, the Indian Ocean southwest of Lampung, the Banda Sea, and the Arafura Sea, which trigger wind convergence areas, convergence, and confluence that can enhance rain cloud growth, both around the circulation centres and along the affected wind pattern areas.
Potential Weather in the Coming Week
In the coming week, BMKG predicts that weather conditions in Indonesia will still be influenced by global, regional, and local atmospheric dynamics.
On a global scale, the El Niño-Southern Oscillation (ENSO) phenomenon is in a neutral phase, as indicated by the NINO 3.4 index of -0.42, which does not significantly increase convective activity in the Indonesian region. Meanwhile, the Dipole Mode Index (DMI) value of -0.25 is also in a neutral phase, showing no significant airflow from the eastern Indian Ocean off Africa to the Indonesian region, particularly the west, so its influence on rainfall distribution in Indonesia remains limited.
On a regional scale, the Australian Monsoon is observed to be strengthening and is forecast to continue strengthening in the coming days. This condition drives an increase in air mass from Australia towards Indonesia, which is generally drier. Consistent with this, analysis shows the dominance of easterly winds in most of Indonesia, indicating that several regions are beginning to experience the transition to the dry season.
The Madden-Julian Oscillation (MJO) phenomenon is forecast to cross much of Sumatra, parts of West Kalimantan, and parts of Papua, potentially increasing rain cloud growth in those areas,” states BMKG in its release on Rain Potential in Indonesia for the Coming Week, period 7-13 April 2026, quoted on Thursday (9/4/2026).
In addition, the Equatorial Rossby wave propagating westward is also forecast to be active, crossing parts of Sumatra, Java, Bali, NTB, NTT, and parts of Papua Island. Meanwhile, the eastward-propagating Kelvin wave is forecast to be active and cross much of Sumatra.
Besides these factors, cyclonic circulations are also potentially forming in the South China Sea, waters north of Aceh, the Indian Ocean southwest of Lampung, the Java Sea, the Sulawesi Sea, and the Banda Sea. These systems form convergence and confluence areas that could enhance rain cloud growth in those regions.
On a local scale, atmospheric lability is also observed to be quite strong in several areas, further supporting convective processes. The areas include Aceh, North Sumatra, Riau, South Sumatra, Lampung, Banten, West Java, Central Java, East Java, NTT, West Kalimantan, South Kalimantan, East Kalimantan, North Kalimantan, Southeast Sulawesi, West Sulawesi, South Sulawesi, Central Sulawesi, Gorontalo, East Nusa Tenggara, Maluku, West Papua, Central Papua, Papua, Papua Mountains, and South Papua.
BMKG Early Warning
The following areas in Indonesia are at risk of moderate to heavy rain in the coming week.
Period 7-9 April 2026
- Moderate to heavy intensity rain is potentially occurring in:
North Sumatra,
West Sumatra,
Riau,
Jambi,
South Sumatra,
Bangka Belitung Islands,
Bengkulu,
Lampung,
Banten,
DKI Jakarta,
West Java,
Central Java,
DI Yogyakarta,
East Java,
Bali,
West Nusa Tenggara (NTB),
East Nusa Tenggara (NTT),
West Kalimantan,
Central Kalimantan,
East Kalimantan,
North Kalimantan,
South Kalimantan,
North Sulawesi,
Central Sulawesi,
West Sulawesi,
South Sulawesi,
Southeast Sulawesi,
North Maluku,
Maluku,
West Papua,
Central Papua,
Papua,
Papua Mountains,
South Papua
- Very heavy intensity rain is potentially occurring in:
North Sumatra,
Lampung,
Banten,
West Java,
East Java,
East Nusa Tenggara (NTT),
Central Sulawesi,
Maluku,
Papua Mountains,
South Papua.
- Strong winds are potentially occurring in:
Bengkulu,
Papua,
West Papua.
Period 10-13 April 2026
- Moderate to heavy intensity rain is potentially occurring in:
Aceh,
North Sumatra,
West Sumatra,
Riau,
Jambi,
South Sumatra,
Bangka Belitung Islands,
Bengkulu,
Lampung,
Banten,
West Java,
Central Java,
D.I Yogyakarta,
East Java,
Bali,
NTB,
NTT,
West Kalimantan,
Central Kalimantan,
East Kalimantan,
North Kalimantan,
South Kalimantan,
North Sulawesi,
Gorontalo,
Central Sulawesi,
West Sulawesi,
South Sulawesi,