BMKG time window for Flores aftershocks points to late-September slowdown
Indonesia’s BMKG expects aftershocks from the 15 August 2026 Flores earthquake to decline over roughly three to four weeks, with activity likely to continue at a lower rate into late September rather than ending on a fixed date.
By Mukmin John
Editor: Mursyid Sonsang
· 4 min read
Labuan Bajo — Indonesia’s meteorological agency BMKG has forecast that aftershocks following the 15 August 2026 Flores earthquake will gradually decline over roughly three to four weeks, but may continue at a lower rate into late September rather than stopping on a fixed date.
BMKG’s deputy for geophysics, Nelly Florida Riama, and the agency’s Director of Earthquake and Tsunami, Wijayanto, outlined the outlook in briefings and statements summarised by national media and in BMKG’s own releases.
According to several reports quoting BMKG’s 19 August assessment, the agency expected aftershock activity to move toward a relatively low level over a period of about three to four weeks, with late September 2026
Those reports emphasised that this was a description of the trend
BMKG’s time window for declining activity
In its 19 August 2026 press information, BMKG said that by 05:00 WIB on that date it had detected thousands of aftershocks with magnitudes between about 1.1 and 6.2 following the main Flores earthquake.
BMKG officials explained that, based on the agency’s models, the rate of aftershocks was expected to become relatively low within roughly three to four weeks, or around late September, although the estimate would be updated as new data came in.
Media citing BMKG stressed that this timeframe was indicative rather than a firm deadline, and that aftershocks could still occur beyond September even if the overall sequence showed a weakening pattern.
BMKG also warned that a lower rate of activity would not mean the sequence had ended completely, and urged residents in affected areas to remain calm but alert while the aftershocks continued.
Later counts: over 13,000 aftershocks by 9 September
Subsequent updates and media coverage reported that by 9 September 2026, BMKG’s monitoring had recorded 13,863 aftershocks in Nusa Tenggara Timur following the Flores mainshock.
BMKG’s update, as cited by outlets including Astakom and RRI, stated that the largest recorded aftershock had a magnitude of about 6.2 and the smallest around 0.9.
The agency noted that its decay graph — which tracks aftershock frequency over time — was beginning to show a downward trend, and reiterated that aftershocks were still expected to continue for around three to four weeks.
Additional coverage in mid-September reported BMKG figures of roughly 14,993 to 15,722 aftershocks by 13–15 September, again with the largest around magnitude 6.2 and around 190 events felt by people, supporting the picture of a large but gradually declining sequence.
Reported monitoring figures
- Main earthquake: magnitude 7.7, on 15 August 2026.
- Aftershocks recorded by 19 August: several thousand, with BMKG citing 2,768 in its press release and media noting around 3,002 in Nusa Tenggara Timur.
- Aftershocks recorded by 9 September: 13,863.
- Largest aftershock reported by 9 September: magnitude 6.2.
- Aftershocks above about magnitude 5: at least two dozen by 19 August, rising to several dozen by early September according to BMKG tallies.
- Felt aftershocks: 81 by 19 August and around 177–190 by early to mid-September.
What BMKG’s forecast does — and does not — say
BMKG’s communications consistently link the three-to-four-week window to a decline in activity, not to a guarantee that aftershocks will stop or that risk has fully passed by the end of September.
The agency’s press releases and quoted remarks do not provide a specific probability for another large aftershock, nor do they present a formal magnitude forecast for individual future events.
Instead, BMKG has focused on describing how the existing sequence is evolving and on advising residents to follow official guidance while the aftershocks move into a lower, but still active, phase.
For travellers, divers and other visitors, the key distinction in BMKG’s messaging is between a forecast of declining aftershock activity and an assurance of complete safety: the agency expects the sequence to weaken overall, but continues monitoring and public communication as the region approaches and moves beyond late September.
Sources
Next story
BNPB: 142 deaths linked to Flores quake, 94 in evacuation sites
Indonesia’s disaster agency says 142 people died in connection with the 15 August 2026 Flores earthquake, including 48 from the direct impact of the m…