MJO

MJO Fortnightly Update

Issued: 31 Jul 2026

 

A weakening Madden-Julian Oscillation (MJO) signal was present over the Western Hemisphere (Phase 8) in late July 2026, based on the RMM index. Most models predict an MJO signal to develop over the Western Pacific (Phase 6) during Week 1 (3 – 9 August), although models disagree whether the signal will continue to propagate or weaken during Week 2 (10 – 16 August).

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

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.
icon

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.