Indonesia’s rainy season is expected to arrive later than usual this year, with the majority of the country not entering the wet season until November, according to the latest forecast from the Meteorology, Climatology and Geophysics Agency (BMKG).
The delay is being linked to a very strong El Niño event, combined with a positive Indian Ocean Dipole (IOD), which has prolonged dry conditions across much of the country. BMKG said 61.08 per cent of Indonesia’s seasonal climate zones are expected to experience a later-than-normal start to the 2026/2027 rainy season.
Despite the delayed arrival of widespread rainfall, the agency has also warned that heavy rain remains possible in several parts of the country, particularly where local atmospheric conditions support the rapid development of rain clouds.
The contrasting conditions mean that Indonesia can still experience heavy rainfall in some areas while much of the country remains in the dry season.
Rainy Season Expected to Peak Between December and February
BMKG’s latest forecast indicates that the rainy season will generally begin in November, although the timing will vary between regions. The agency expects the season to reach its peak in December 2026, January 2027 or February 2027, depending on the area.
December is expected to be the peak month across the largest proportion of the country. BMKG estimates that 155 seasonal climate zones, covering 36.94 per cent of Indonesia’s land area, will experience their peak rainfall in December.
A further 162 zones, covering 25.68 per cent of the country’s land area, are expected to reach peak rainfall in January 2027. Another 190 zones, covering 16.79 per cent of the land area, are forecast to reach their peak in February 2027.
Areas expected to see their rainy-season peak in December include much of Sumatra and Kalimantan, parts of northern Sulawesi, Gorontalo, Sulawesi Tengah and Sulawesi Barat, as well as several areas of Maluku and Papua.
The forecast means that the arrival of the rainy season will not be uniform across Indonesia. Some locations may begin receiving more regular rainfall in November, while others may remain relatively dry for longer.
BMKG also expects the 2026/2027 rainy season to be shorter than usual. Nevertheless, the agency estimates that rainfall characteristics will remain within the normal range across 510 seasonal climate zones, equivalent to 69.76 per cent of Indonesia’s land area.
Another 147 zones, covering 18.55 per cent of the land area, are forecast to experience wetter-than-normal conditions, while 42 zones, covering 11.69 per cent, could remain drier than normal.
This creates a complicated weather outlook for the coming months. The delayed start means the country will have a longer dry period, but the eventual arrival of the wet season could still bring periods of intense rainfall.
BMKG Head Teuku Faisal Fathani said the combination of El Niño and a positive IOD had contributed to the prolonged dry conditions.
“The combination of the El Niño and IOD phenomena occurring simultaneously worsens and prolongs the drought period across much of Indonesia, causing the rainy season to arrive later and last for a shorter period,” Faisal said, as reported by Media Indonesia.
Very Strong El Niño Keeps Indonesia Dry
The current conditions are closely associated with the strength of El Niño in the Pacific Ocean.
BMKG recorded a sea-surface temperature anomaly of +2.83°C in the Nino3.4 region of the Pacific Ocean at the end of August 2026. The agency also recorded an ENSO index of +2.63 for the July-August-September period, indicating a very strong El Niño phase.
The agency expects the ENSO conditions to remain in place until early 2027, although the influence of El Niño is expected to weaken as the rainy season develops.
The prolonged dry conditions are already affecting several sectors, particularly agriculture.
According to Media Indonesia, BMKG recorded 556 seasonal climate zones, equivalent to 61.91 per cent of Indonesia’s land area, as still experiencing the dry season. The publication also reported that Agriculture Minister Andi Amran Sulaiman estimated around 50,000 hectares of agricultural land had been affected by drought as of 14 September.
In East Java, 3,856 hectares of agricultural land had reportedly been affected by drought as of 10 September, including 597.11 hectares of rice fields. Of that figure, 149.95 hectares had experienced crop failure.
The government has consequently been using available water resources to support affected communities and agricultural areas. The Ministry of Public Works reported that it had addressed drought conditions at 1,229 locations as of 21 August, helping protect approximately 41,252 hectares of rice fields and provide clean water for more than 616,000 people.
The extended dry season has also increased the risk of forest and land fires in several parts of the country.
However, the presence of El Niño does not mean that every part of Indonesia will remain completely dry. Local atmospheric conditions can still produce significant rainfall, even during a broader period of drought.
Heavy Rain Still Possible in Parts of Sumatra
Recent weather patterns have demonstrated the contrast between Indonesia’s overall climate conditions and local weather events.
BMKG has recorded periods of moderate to very heavy rainfall in several parts of the country despite the ongoing dry season. Between 14 and 16 September, for example, the highest daily rainfall totals were recorded in Aceh and West Sumatra, both reaching 138 millimetres per day. North Kalimantan recorded 83 millimetres, North Sumatra 61 millimetres and Papua 56 millimetres.
The possibility of heavy rain is partly linked to atmospheric waves and wind patterns that can temporarily increase moisture and cloud formation.
BMKG has identified activity from the Equatorial Rossby and Kelvin waves in different parts of Indonesia, alongside convergence zones and areas where winds change direction or slow down.
These conditions can encourage the development of rain clouds in specific regions even when the wider climate pattern remains dry.
This explains why heavy rainfall can occur in parts of Sumatra while other regions are experiencing prolonged dry weather.
For the period from 18 to 24 September, BMKG forecast moderate to very heavy rainfall in a number of areas, including parts of Sumatra, Kalimantan, Sulawesi and Papua. The agency also warned of possible thunderstorms and strong winds in areas affected by heavier rainfall.
The situation is particularly relevant in northern and western Sumatra, where atmospheric activity can support the development of rain clouds even though Indonesia remains under the broader influence of El Niño.
At the same time, areas that remain dry continue to face the risk of forest and land fires. BMKG has reported long rain-free periods in parts of southern Sumatra, Java, southern Kalimantan, Bali, Nusa Tenggara and several areas of Sulawesi and Papua.
