MJO

MJO Fortnightly Update

Issued: 17 Dec 2025

 

There was no Madden-Julian Oscillation (MJO) signal present by the middle of December 2025, based on the RMM Index.  Most models predict no sustained MJO signal during the forecast period (22 Dec 2025 – 4 Jan 2026).

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.