Dry-season forecasts leave Bali’s local flood risks in place

Denpasar — Indonesia’s weather agency has forecast generally low rainfall for Bali in mid-September, but both BMKG and Bali’s provincial disaster agency say localised heavy rain and existing vulnerabilities mean flood risk has not disappeared.

In its national weekly outlook for 8–14 September 2026, issued on 7 September, the Meteorology, Climatology and Geophysics Agency (BMKG) said rainfall in much of Indonesia during September was expected to stay in the low to medium range of 0–150 millimetres per 10‑day period. BMKG highlighted that rainfall below 50 millimetres per 10‑day period was likely to dominate in southern Sumatra, Java, Bali, Nusa Tenggara, Kalimantan, Sulawesi, Maluku and parts of Papua.

Although the dry season still dominates most regions, BMKG noted that rain remains possible in parts of Sumatra, Kalimantan, western Java and Papua during 8–14 September, and that day‑to‑day conditions can vary between areas even within one province. Earlier guidance covering late August into early September also pointed to a generally dry pattern for Bali and Java as El Niño strengthened and limited atmospheric moisture over much of Indonesia.

Dry-season outlook, but local rain still a concern

BMKG attributed the broadly dry pattern in late August and early September to a strong El Niño event reducing the moisture supply to Indonesia and to otherwise limited atmospheric humidity. At the same time, the agency cautioned that local factors such as surface heating, topography, available moisture and interactions between land and sea breezes can rapidly trigger rain clouds and short‑lived showers, even when the wider region remains in drought‑like conditions.

For Bali, this means that a short, intense downpour over a single watershed can cause disruptive flooding that is not visible in province‑wide rainfall averages. The impact of such bursts depends not only on total rainfall but also on intensity and duration at specific catchments, river capacity, drainage, solid waste accumulation and the extent of paved or built‑up land. These drivers are highlighted in Bali’s 2025–2029 disaster risk assessment, which identifies flooding as a key hazard in several districts.

The provincial disaster management agency (BPBD Bali) has used its early‑warning briefings in September to emphasise that residents and visitors should remain vigilant despite the dominance of dry‑season conditions. In its early‑warning bulletin for the second 10‑day period of September, the agency reported that Bali is still in the dry season and that the main meteorological threat remains drought, not high rainfall.

September guidance from BPBD Bali

According to BPBD Bali’s early‑warning bulletin for Dasarian II (11–20 September 2026), light rain is possible on 11–13 September and again on 14–16 September across all major districts, including Badung, Denpasar, Gianyar, Klungkung, Tabanan, Jembrana, Bangli, Karangasem and Buleleng. The same bulletin states there is an early warning for meteorological drought during this period, but no early warning for high rainfall, underlining that water scarcity remains a priority concern.

BPBD Bali has complemented these notices with preparedness measures in flood‑prone urban areas. In mid‑September, the agency reported the installation of siren‑based early‑warning equipment along Tukad Badung in central Denpasar, aimed at giving residents, traders and visitors near the Badung and Kumbasari markets more time to react if river levels rise quickly.

Reading forecasts at the right scale

BMKG’s weekly national outlooks provide a useful picture of the dominant weather pattern but are not a guarantee of dry conditions in every district or street. A low rainfall category for Bali as a whole can coexist with a high‑impact local storm focused over one drainage basin, especially where rivers are heavily constrained and urban development has encroached on natural floodplains.

For practical decisions, residents and visitors are advised to combine BMKG’s national outlooks with short‑range warnings and local information. BMKG updates give near‑term guidance on rain and severe weather, while BPBD Bali bulletins and risk maps offer province‑level information on vulnerable areas, preparedness actions and evolving hazards, from drought to flooding.

The forecast period of 8–14 September covered by the 7 September national outlook has now ended, so travellers and local communities should refer to the most recent BMKG and BPBD Bali advisories for any new alerts or changes in risk.

Sources

• BMKG – Prakiraan Cuaca Indonesia Sepekan Periode 8–14 September 2026
• BPBD Provinsi Bali – Peringatan Dini Cuaca/Iklim Dasarian II September 2026 Provinsi Bali
• Balipost – Dasarian II September, Bali Masih Periode Musim Kemarau