Why the Rainy Season is Delayed and Will Be Shorter in Duration
The Meteorology, Climatology, and Geophysics Agency (BMKG) predicts that the rainy season will be delayed and its duration will be shorter. BMKG has revealed its forecast for the 2026 rainy season, predicting that the start of the rainy season in Indonesia will occur in November 2026.
“The start of the 2026/2027 rainy season will occur gradually. Most parts of Indonesia are predicted to enter the rainy season in the November 2026 period, covering 185 seasonal zones or 24.66% of Indonesia’s land area,” stated the Head of BMKG, Teuku Faisal Fathani, during a press conference on Tuesday (22/09/2026).
Subsequently, the rainy season will continue into the December period, with 17.31% of Indonesia’s territory receiving rainfall. “The rainy season in the December 2026 period will cover 266 seasonal zones or 17.31% of Indonesia’s land area,” he continued.
Faisal explained that the rainy season will arrive later in some parts of Indonesia. “The start of the rainy season in some parts of Indonesia is predicted to arrive later or be delayed, affecting 529 zones or 61.08% of Indonesia’s land area,” said Faisal.
Peak of the Rainy Season
BMKG predicts the peak of the rainy season will occur in December 2026. “Most parts of Indonesia are predicted to experience the peak of the rainy season in December 2026, covering 155 seasonal zones or 36.94 per cent of Indonesia’s land area,” said Faisal.
Meanwhile, the peak of the rainy season will continue into January 2027. Faisal noted that the rainy season in January 2027 will occur in 162 seasonal zones or 25.68% of Indonesia’s land area. “Then in February 2027, it will cover 190 seasonal zones or 16.79% of Indonesia’s land area,” he explained.
Areas Without Rain
The Deputy for Climatology at BMKG, Ardhasena Sopaheluwakan, stated that the region experiencing the most extreme number of rainless days, leading to drought, is currently Bantul, Special Region of Yogyakarta (DIY).
“Many observation locations have reported more than 60 consecutive rainless days, spread across 25 provinces, with the longest period of no rain currently in the Bantul region, lasting 131 days or more than 4 months,” Ardhasena said during the same session.
Ardhasena explained that the intensity of El Niño this year is considered strong. Sea surface temperature anomaly data in the Pacific Ocean as of late August reached 2.83, with a quarterly average (July-August-September) of 2.63.
Historically, he continued, El Niño always extends and worsens the dry season in Indonesia, particularly in regions south of the Equator. This phenomenon is predicted to persist until early next year.
“For now, it will persist at least until the end of the first quarter of 2027. However, its impact on drought in Indonesia will conclude once we enter the rainy season,” he explained.
Ardhasena added that this year’s climate anomaly has even created anomalies in Indonesia’s climate zones. Regions that are naturally accustomed to rainfall throughout the year are now also being affected by the dry season.
“Climatologically, Indonesia has 110 seasonal zones or 33% of the land area where the climate characteristic is rainfall throughout the year. However, for 2026, 98 of those seasonal zones are experiencing a dry season due to the impact of lower rainfall anomalies caused by El Niño, while the other 12 seasonal zones remain unchanged from their climatological norms,” concluded Ardhasena.
Causes of the Delayed Rainy Season
BMKG revealed that the cause of the delayed rainy season is the El Niño phenomenon.
“The combination of the El Niño and IOD (Indian Ocean Dipole) phenomena occurring simultaneously is exacerbating and lengthening the drought period in most parts of Indonesia, causing the rainy season to arrive late and occur more briefly,” said Faisal.
The Acting Deputy for Meteorology at BMKG, Andri Ramdhani, noted that the duration of this rainy season is relatively shorter. Nevertheless, the accumulation of rainfall is predicted to be above normal, meaning the potential for heavy rainfall with high intensity is very high.
“This rainy season period is short, but rainfall is generally higher than normal. This is what needs to be watched,” said Andri.
“Therefore, heavy rain may fall intensely during those months, and for regions that have historically experienced ‘wet’ hydrometeorological disasters, vigilance is necessary,” he continued.
Andri mentioned that regions that have historically experienced wet hydrometeorological disasters need to increase their alertness. He identified these wet regions.
“Generally, it is in the Java region; I believe Java is widespread, especially West Java which is the highest, followed by Central Java and East Java. Also, for the Sumatra region, attention is needed in Padang, Sumatra, as well as North Sumatra and Aceh,” he added.