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Subseasonal Weather Outlook and Review

Review of Regional Weather for July 2026

 

1. Overview

1.1 During July 2026, a mix of near- to above-average rainfall was recorded over the ASEAN region (Figure 1). Parts of western and eastern Mainland Southeast Asia recorded above-average rainfall while central parts of Mainland Southeast Asia recorded below-average rainfall based on the two datasets (GSMaP-NRT and CMORPH-Blended). Elsewhere, the northwestern Maritime Continent recorded mostly above-average rainfall, with most of the northwestern Maritime Continent and equatorial region recording below-average rainfall. The largest positive (wetter) anomalies were recorded over western Myanmar and southern Malay Peninsula, with the largest negative (drier) anomalies over Sulawesi and the Maluku Islands.

1.2 The observed rainfall anomaly pattern of above-average rainfall over western Mainland Southeast Asia and the below-average rainfall over the southern and eastern Maritime Continent are consistent with the predictions from the subseasonal weather outlooks for July 2026 (6 – 19 July 2026 and 20 July – 2 August 2026). The wet anomalies over western Mainland Southeast Asia and the dry anomalies over the eastern Maritime Continent are consistent with the seasonal outlook for July 2026.

era5_rainfall_anomalies
cmorph_bld_rainfall_anomalies
Figure 1: Rainfall anomalies for July 2026 based on GSMaP-NRT data (left) and CPC Global Unified Gauge-based Analysis data (right). The climatological reference period is 2001-2024. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

 

1.3 For Mainland Southeast Asia, below-average temperature was recorded over parts of northern region, with above-average temperature over the southeastern parts and near-average temperature elsewhere (Figure 2). For much of the Maritime Continent, above-average temperature was recorded. The warmest anomalies (1°C – 2°C above average) were recorded over southern Sumatra. The coolest anomalies (-0.25°C – -0.5°C below average) were recorded over parts of northern Lao PDR.

era5_temperature_anomalies
Figure 2: Temperature anomalies for June 2026 based on ERA-5 reanalysis. The climatological reference period is 2001-2024. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

 

2. Climate Drivers

2.1 The Madden-Julian Oscillation (MJO) was active over the Western Pacific and Western Hemisphere during much of July 2026. In Week 1, an MJO signal was present in the Western Pacific (Phase 7). In Week 2, the MJO signal propagated eastwards to the Western Hemisphere (Phase 8), staying in the Western Hemisphere (Phases 8) in Week 3, before decaying in Week 4 and becoming inactive by the end of the month. Phases 7 and 8 tend to bring drier conditions to much of the ASEAN region. This is somewhat in line with the drier conditions over the eastern Maritime Continent in Figure 1.

mjo_phase_diagram

 

Figure 3: The MJO phase diagram. The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator (denoted in the text with the first day of the month in blue and the last day of the month in red). The distance of the index from the centre of the diagram is related to the strength of the MJO. Values within the grey circle are considered weak or indiscernible (data from the Bureau of Meteorology, Australia)..

 

2.2 The El Niño conditions are now present in July 2026, with the Indian Ocean Dipole (IOD) in the neutral state. El Niño conditions can bring drier conditions to the Maritime Continent at this time of the year.