MJO
MJO Fortnightly Update
Issued: 23 Oct 2025
A Madden-Julian Oscillation (MJO) signal was present over the Indian Ocean (Phase 2) in the middle of October. Models predict continued eastward propagation of the MJO signal to the Maritime Continent (Phase 4) by the start of the forecast period. For Week 1 (27 October – 2 November), models predict the MJO to weaken over the Maritime Continent (Phases 4 and 5), with some predicting the signal to continue propagating over the Western Pacific (Phases 6 and 7) in Week 2 (3 – 9 November).
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.