Australian Monsoon Winds Surge, Influencing Indonesia’s Dry Season

Forecasters Predict Shift with Potential for Expanded Dry Zones Amidst Continued Rainfall Risks

Indonesia’s weather outlook is set to change significantly as the Australian monsoon winds are expected to strengthen considerably in the coming week, a shift that could accelerate the onset of the dry season in various regions. However, the nation must still contend with a high probability of heavy rainfall across several areas.

Monsoon Winds to Strengthen

The Meteorology, Climatology, and Geophysics Agency (BMKG) has forecast a robust return of Australian monsoon winds from July 18 to July 25, 2025. This marks a notable departure from recent weeks, when weaker-than-average monsoon activity contributed to delayed dry season conditions in numerous Indonesian seasonal zones.

BMKG indicated in its Weekly Weather Outlook that these anticipated wind patterns may help enlarge the territories transitioning into the dry season. This development follows a period where only about 39 percent of Indonesia’s seasonal zones had officially entered the dry season by the first third of July.

Regions Experiencing Dry Season and Persistent Rainfall

The initial dry spell has predominantly affected provinces in Sumatra, including most of Aceh, North Sumatra, West Sumatra, Bengkulu, Riau, Riau Islands, Jambi, and South Sumatra, with a small section of Lampung also included. In the country’s southern areas, parts of Banten, West Java, Central Java, and East Java have seen dry season indicators, alongside limited spots in Bali, West Nusa Tenggara (NTB), and East Nusa Tenggara (NTT).

Early signs of drier weather have also emerged in sections of South Kalimantan, South Sulawesi, West Papua, and Papua. Despite these localized dry conditions, the BMKG has recorded significant rainfall events across the archipelago.

Between July 15 and 16, heavy to extreme rainfall was observed, particularly in Fakfak, West Papua, which recorded an exceptional 334.4 mm and 206.5 mm in a single day. Similar heavy precipitation was reported in Gorontalo (95.4 mm), Poso in Central Sulawesi (85.5 mm), and Jakarta (80 mm) on July 16.

Outlook for Continued Heavy Rainfall

Looking ahead, the potential for intense rainfall remains elevated for the upcoming week, with South Sumatra, western Java, and many central and eastern Indonesian regions likely to experience this weather phenomenon. This is attributed to the presence of two tropical cyclone seeds: 90S in the Indian Ocean west of Sumatra, and 96W in the Philippine Sea.

The BMKG also issued a warning that tropical cyclone seed 90S could generate significant waves, reaching up to 4 meters high in several maritime areas. These include the waters west of Enggano, west of Lampung, south of Banten and West Java, as well as the Indian Ocean west of Bengkulu and south of Lampung stretching to Banten and West Java.

The increased activity of the Australian monsoon is a natural shift in seasonal patterns. For comparison, the Australian Bureau of Meteorology recently reported that La Niña conditions, which often bring wetter weather to eastern Australia, had weakened in late 2023, leading to a transition to ENSO-neutral conditions, similar to the shifts seen in Indonesian weather patterns (Bureau of Meteorology, Australia).