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MJO Fortnightly Update
Issued: 21 Oct 2026
In the middle of October, a Madden-Julian Oscillation (MJO) signal was present over the Western Hemisphere and Africa (Phase 1) based on the RMM Index. There is considerable uncertainty in the MJO outlook during the forecast period. While most models predict an MJO-like signal to develop over the Indian Ocean (Phases 2 and 3) in Week 1 (26 October – 1 November), this is similar to the forecast by some models from two weeks ago that did not transpire.
Period:
Location:
Figure 1: Below-normal and Above-normal rainfall frequencies for MJO phases based on GPCP (reference period: 2001-2020).
For each MJO phase, the below- and above-normal rainfall frequencies are computed as the ratio of days with values exceeding the lower upper tercile thresholds, respectively, 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 anomalies 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.