Category Archives: Regional Weather Review for Year 2026

Regional Weather Review for Year 2026

May 20, 2026

Review of Regional Weather for April 2026

1. Overview

1.1 During April 2026, below- to near-average rainfall was recorded over most of Mainland Southeast Asia with a mix of below- to above-average rainfall for the Maritime Continent (Figure 1). Most of southern and central Mailand Southeast Asia recorded below-average rainfall based on both datasets (GSMaP-NRT and CMORPH-CRT). The western and southern Maritime Continent recorded predominately above-average rainfall, with the northeastern part recording below-average rainfall and the central Maritime Continent a mix of below- to above-average rainfall. The largest positive (wetter) anomalies were recorded over Sumatra for both datasets, along with parts of the southern Maritime Continent for CMORPH-CRT, with the largest negative (drier) anomalies over northwestern Borneo for both datasets and Sulawesi for GSMaP-NRT).

1.2 The observed rainfall anomaly pattern of below-average rainfall over southern and central Mainland Southeast Asia as well as over the northern Maritime Continent, is consistent with the predictions from the subseasonal weather outlooks for March 2026 (30 March – 12 April 2026, 13 – 26 April 2026) and 27 April – 10 May 2026). However, the seasonal outlook predicted below-normal rainfall as the dominant tercile for much of the southern ASEAN region.

Figure 1: Rainfall anomalies for April 2026 based on GSMaP-NRT data (left) and CPC CMORPH-CRT 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 Above-average temperature was recorded over parts of northeastern Mainland Southeast Asia, with below- to near-average temperature for southeastern and northwestern Mainland Southeast Asia (Figure 2). Near-to above-average temperature was recorded for much of the ASEAN region. The warmest anomalies (2°C – 3°C above average) were recorded over parts of Viet Nam and Lao PDR, with warm anomalies (1°C – 2°C above average) recorded over parts of Thailand and Cambodia. The coolest anomalies (0.5°C – 1°C below average) were recorded over parts of Myanmar, Papua and around Timor Leste.

Figure 2: Temperature anomalies for April 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 for much of April. At the start of April, an MJO signal quickly decayed and was inactive by the end of the first week. An MJO signal then developed over the Western Pacific (Phases 6 and 7) in the second week. This signal continued propagating eastward through the Western Hemisphere, reaching the Indian Ocean (Phase 2) by the end of the month. At this time of the year, Phases 7 and 8 tend to bring drier conditions to the Maritime Continent, with Phase 1 also tending to bring drier conditions to the central and eastern Maritime Continent, and Phase 2 bringing wetter conditions to the western Maritime Continent. This is somewhat in line with drier conditions over parts of the eastern Maritime Continent in Figure 1.

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 – Southern Oscillation (ENSO) was neutral in April, with the Indian Ocean Dipole (IOD) also in the neutral state.

April 17, 2026

Review of Regional Weather for March 2026

1. Overview

1.1 During March 2026, below-average rainfall was recorded over much of the Maritime Continent with a mix of below and near-average rainfall over most of Mainland Southeast Asia (Figure 1). Mix of below- to above-average (wetter) anomalies were also observed over parts of the eastern equatorial region for both datasets (GSMaP-NRT and CMORPH-CRT). There were dry anomalies over much of central and southern Mainland Southeast Asia, with some regions of above-average rainfall over parts of Viet Nam and northern Myanmar. The largest positive (wetter) anomalies were recorded over Papua for GSMaP-NRT, and over northern Myanmar and western Sumatra for CMORPH-CRT, with the largest negative (drier) anomalies over northwestern Borneo for both datasets.

1.2 The observed rainfall anomaly pattern of below-average rainfall over the Maritime Continent, where the highest anomalies are recorded, is consistent with the predictions from the subseasonal weather outlooks for March 2026 (2 – 15 March 2026 and 16 – 29 January 2025). The subseasonal weather outlooks predicted a drier central Maritime Continent, which is more consistent with the recorded rainfall from CMORPH-BLD. The below-average rainfall over the Maritime Continent is also consistent with the seasonal rainfall outlook for March, with higher confidence of below-normal rainfall over the central region predicted.

Figure 1: Rainfall anomalies for March 2026 based on GSMaP-NRT data (left) and CPC CMORPH-CRT 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 Above-average temperature was recorded over parts of northeastern Mainland Southeast Asia, with below- to near-average temperature for southeastern and northwestern Mainland Southeast Asia (Figure 2). Below-average temperature was recorded for the northeastern and southeastern Maritime Continent, while near- to above-average temperature was recorded for western and central Maritime Continent. The warmest anomalies (2°C – 3°C above average) were recorded over northern Viet Nam, while the coolest anomalies (0.5°C – 1°C below average) were recorded over eastern Myanmar, northern Philippines and eastern Cambodia.

Figure 2: Temperature anomalies for March 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 inactive for much of March based on the RMM diagram (Figure 3). The signal was inactive during the beginning of March, then emerged shortly in Week 3 over the Western Pacific (Phase 7), propagating to Western Hemisphere (Phase 8) and then decayed over the Western Hemisphere (Phase 8) in the same week. The MJO signal remained indiscernible for much of Week 4, before emerging over the Western Hemisphere (Phase 1) at the end of the month. At this time of the year, Phases 7 and 8 tend to bring drier conditions to the Maritime Continent, with the observed rainfall in March also showing drier conditions.

2.2 The El Niño – Southern Oscillation (ENSO) condition is “Neutral”. The Indian Ocean Dipole (IOD) is currently in the neutral state.

March 13, 2026

Review of Regional Weather for February 2026

1. Overview

1.1 During February 2026, above-average rainfall was recorded over much of the northern half of the Maritime Continent with near-average rainfall over most of Mainland Southeast Asia (Figure 1). While above-average (wetter) anomalies are observed distributed over much of northern half of the area for both datasets (GSMaP-NRT and CMORPH-BLD), there is disagreement elsewhere over the Maritime Continent. GSMaP-NRT recorded above-average anomalies but CMORPH-BLD recorded mainly below-average (drier) anomalies for much of the southern half of the Maritime Continent. There were no notable anomalies over most of Mainland Southeast Asia, in line with the current dry season, with some regions of above-average rainfall over parts of Viet Nam. The largest positive (wetter) anomalies were recorded over southern Philippines for both datasets, with the largest negative (drier) anomalies over southern Borneo for CMORPH-BLD.

1.2 The observed rainfall anomaly pattern of above-average rainfall over the northeastern Maritime Continent, where the highest anomalies are recorded, is consistent with the predictions from the subseasonal weather outlooks for February 2025 (2 – 15 February 2026, and 16 Febraury – 1 March 2025). The subseasonal weather outlooks predicted a drier central Maritime Continent, which is more consistent with the recorded rainfall from CMORPH-BLD. The observations match the most likely tercile from the seasonal outlook for February 2026 for northeastern Maritime Continent where the rainfall observed the largest positive anomalies.

Figure 1: Rainfall anomalies for February 2026 based on GSMaP-NRT data (left) and CPC CMORPH-CRT 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 Above-average temperature was recorded over most of Mainland Southeast Asia, with below- to near-average temperature for southeastern Mainland Southeast Asia (Figure 2). For the Maritime Continent, near-average temperature was generally recorded. The warmest anomalies (2°C – 3°C above average) were recorded over northern Viet Nam, while the coolest anomalies (0.5°C – 1°C below average) were recorded over Papua and central Cambodia.

Figure 2: Temperature anomalies for February 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 At the start of January, the Madden-Julian Oscillation (MJO) was inactive based on the RMM diagram (Figure 3). The signal emerged over the Western Pacific (Phase 6) in Week 2, strengthening with little eastward propagation in Phase 6 until middle of Week 3 when it weakened slightly and started again propagating eastwards. By Week 4, the MJO signal was in Phase 7 of the Western Pacific where it stalled and weakened at the end of the month. At this time of the year, Phases 6 and 7 tend to bring drier conditions to the western and southern Maritime Continent, in line with the observed rainfall in January also showing drier conditions for much of the Maritime Continent.

Figure 3: The Madden-Julian Oscillation (MJO) was inactive for much of February based on the RMM diagram (Figure 3). The signal decayed over the Western Hemisphere (Phase 8) at the beginning of the month , before emerging shortly in the middle of February over the Indian Ocean (Phases 2 and 3) and decaying again after a week. The MJO signal remained indiscernible for much of Week 4, before emerging over the Maritime Continent (Phases 4 and 5) at the end of the month. At this time of the year, Phases 2 and 3 as well as Phases 4 and 5 tend to bring wetter conditions to the Maritime Continent, with the observed rainfall in February also showing wetter conditions (data from the Bureau of Meteorology, Australia).

2.2 La Niña conditions persisted and continued weakening in February 2026. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during this time of the year. The Indian Ocean Dipole (IOD) is currently in the neutral state.

February 20, 2026

Review of Regional Weather for January 2026

1. Overview

1.1 During January 2026, below- to near-average rainfall was recorded over much of the Maritime Continent with near-average rainfall over Mainland Southeast Asia (Figure 1). For the Maritime Continent, most of the equatorial region recorded below-average (drier) anomalies, with scattered spots of near- to above-average (wetter) anomalies for the southern and northeastern regions for both datasets (GSMaP-NRT and CMORPH-CRT). There were no notable anomalies over Mainland Southeast Asia, in line with the current dry season. The largest positive (wetter) anomalies were recorded over central Philippines, with the largest negative (drier) anomalies over western Borneo.

1.2 The observed rainfall anomaly pattern of below-average rainfall over much of the equatorial region and the above-average rainfall over northeast Maritime Continent is consistent with the predictions from the subseasonal weather outlooks for January 2025 (22 December 2025 – 4 January 2026, 5 – 18 January 2025, and 19 January – 1 February 2026). The observations match the most likely tercile from the seasonal outlook for January 2026 for central and northeastern Maritime Continent where the rainfall observed the largest drier and wetter anomalies, but differ for much of the rest of the Maritime Continent.

Figure 1: Rainfall anomalies for January 2026 based on GSMaP-NRT data (left) and CPC CMORPH-CRT 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 Above-average temperature was recorded over the eastern Maritime Continent and parts of northern Mainland Southeast Asia, while below-average temperature was recorded over central and southern Mainland Southeast Asia, with near-average temperature for much of the rest of Southeast Asia (Figure 2). The warmest anomalies (1°C – 2°C above average) were recorded over western Myanmar, while the coolest anomalies (1°C – 2°C below average) were recorded over Cambodia, southern Viet Nam and central Thailand.

Figure 2: Temperature anomalies for January 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

2.2 La Niña conditions persisted in January 2026, although key atmospheric indicators show signs of the La Niña conditions weakening. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during this time of the year. The Indian Ocean Dipole (IOD) is currently in the neutral state.