MJO

MJO Fortnightly Update

Issued: 8 Oct 2025

There was no significant Madden-Julian Oscillation (MJO) activity in the first week of October. Most models predict development of an MJO signal over the Western Hemisphere and Africa (Phases 8 and 1) near the start of the forecast period, propagating to the Indian Ocean (Phase 2) in Week 1 (13 – 19 October). Some models predict the signal to continue propagating and reach the Maritime Continent (Phase 4) in Week 2 (20 – 26 October).

ALL Western MC Central MC Southern MC Eastern MC Central MSA Philippines
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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.
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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.