Indonesia’s weather outlook for 23–29 October combines largely dry, hot conditions with sharply localised rain and updated warnings for heavy downpours and strong winds. Recent observations show that very high temperatures and substantial rainfall have occurred in different parts of the country at the same time, while the forecast sets out separate risk areas for the two halves of the coming week.
Very hot conditions alongside intense local rain
Maximum temperatures recorded on 21 October reached 39.2°C in Lampung and 39°C in West Java. South Kalimantan recorded a maximum of 38.7°C on 20 October. The weather agency’s assessment links reduced cloud cover and limited rainfall with stronger daytime surface heating and faster loss of moisture from vegetation. It says these conditions can increase vulnerability to forest and land fires; they do not establish that a particular fire was caused by the heat.
The same assessment recorded heavy to extreme daily rainfall between 19 and 21 October. The highest listed total was 190.6 millimetres in North Sumatra, followed by 130.7mm in West Sumatra and 119mm in Aceh. West Kalimantan recorded 83mm, while Central Papua recorded 78mm. These are reported daily rainfall amounts, not forecasts or evidence that flooding or damage occurred.
Recent rain was associated with several atmospheric influences, including the Madden–Julian Oscillation, Kelvin and mixed Rossby–gravity waves, wind convergence and slowing, and relatively warm sea-surface temperatures. Such factors can support the growth of rain-bearing clouds, particularly in parts of northern and western Sumatra and Kalimantan.
Warnings differ between the two forecast periods
For 23–25 October, conditions nationally are expected to be mostly partly cloudy to lightly rainy, but moderate rain is possible in a number of areas. The warning for heavy to very heavy rain, classified as “Siaga”, covers Aceh, North Sumatra, West Sumatra, Riau, West Java and North Kalimantan. Strong winds are also possible in Bangka Belitung, Lampung, Banten, West Java, Central Java, West Kalimantan, Central Kalimantan, South Kalimantan and South Sulawesi.
For 26–29 October, the broadly partly cloudy to light-rain pattern remains in the outlook, with moderate rain possible in areas including Aceh, North Sumatra, West Sumatra, Riau Islands, Jambi, South Sumatra, Bangka Belitung, Bengkulu, Yogyakarta, parts of Kalimantan, North Sulawesi and parts of Papua. The “Siaga” heavy-to-very-heavy-rain warning shifts to Riau, West Java and Central Java. Potential strong winds are listed for Aceh, Banten, West Java, East Nusa Tenggara, South Sulawesi and South Papua.
These are areas of potential weather, not reports of impacts. A generally low-to-moderate rainfall outlook over a longer period does not rule out intense rain on particular days. Regional atmospheric activity and local conditions can still support thunderstorms, gusts and significant local downpours.
Hotspot detections prompt continued fire vigilance
Over the ten days preceding the update, the agency reported the largest number of high-confidence hotspot detections in Central Kalimantan, at 3,794. South Sumatra had 1,595 and South Papua 1,516. Hotspots are detections that warrant attention, but the counts alone do not confirm the number, size or impact of damaging fires. Smoke was also reported as detected in parts of Sumatra, Kalimantan, Sulawesi, Maluku and Papua.
The agency has urged people and local authorities to use water carefully during dry conditions, avoid burning rubbish or clearing land by fire, and report signs of flames. It also advises people to protect themselves from strong sun and drink enough fluids when outdoors during the day. Localised rain may bring its own hazards, including possible waterlogging, landslides and lightning, so residents are advised to keep watch for updated official warnings.
The revised outlook was issued in Jakarta on 22 October and updated at 18:00 local time. Its message is not that Indonesia will be uniformly dry or uniformly wet: heat and fire vulnerability remain concerns in some locations, while other areas face the possibility of heavy rain, thunderstorms or strong winds during the coming week.
