MJO
MJO Fortnightly Update
Issued: 30 Sep 2025
No coherent Madden-Julian Oscillation (MJO) signal was present at the start of September.
Most models predict no significant MJO activity during the forecast period.
Figure 1: Upper-tercile rainfall frequency for MJO phases based on GPCP (reference period: 2001-2020).
For each MJO phase, the upper tercile frequency is computed as the ratio of days with values exceeding the upper tercile threshold to the total number of days in that phase.
N corresponds to the number of days for each MJO phase.
Figure 2: Correlation heatmap between RMM amplitude and 20–90 days bandpass-filtered daily rainfall based on GPCP data (Reference period: 2001–2020); Only correlation significant at the 95% level is shown.
MC = Maritime Continent; MSA = Mainland Southeast Asia.
The qualitative outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.