Review of Regional Weather for January 2024


1. Overview

1.1 During January 2024, a mix of below- to above-average was recorded over the Maritime Continent, with much of the central and western parts receiving above-average rainfall, and the northeastern parts receiving below-average rainfall (Figure 1). Over Mainland Southeast Asia, near-average rainfall was recorded in January. The largest positive (wetter) anomalies were recorded over southern Philippines and southern parts of the Malay Peninsula based on GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. In contrast, the largest negative (drier) anomalies were recorded over central Philippines (in both GSMaP-NRT and CMORPH-Blended).

1.2 The observed rainfall anomaly pattern of above-average rainfall over most of the western half of Maritime Continent, the drier than average conditions over the northeastern parts of the Maritime Continent, and the near-average rainfall over Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for January 2024 (25 December 2023 – 7 January 2024, 8 – 21 January 2024 and 22 January – 4 February 2024).

Figure 1: Rainfall anomalies for January 2024 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2023. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).


1.3 Above-average temperatures were recorded over the Maritime Continent and much of Mainland Southeast Asia (Figure 2) in January 2024. The exceptions were over parts of Myanmar and Cambodia, where below-to near-average temperature was recorded. The warmest anomalies (more than 1°C above average) were recorded over Thailand, Lao PDR, northern Viet Nam, Sulawesi, and eastern parts of Borneo.



Figure 2: Temperature anomalies for January 2024 based on ERA-5 reanalysis. The climatological reference period is 2001-2023. 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 throughout the entire month of January, based on the RMM index (Figure 3). In the first and second weeks of January, an active MJO signal was present over the Indian Ocean (Phases 2 and 3). In the third week of the month, the active MJO signal was propagating eastwards through the Maritime Continent (Phases 4 and 5) and remained active during the last week over the Western Pacific (Phases 6 and 7). Typically for January, Phase 3 tends to bring wetter conditions for western Maritime Continent, Phase 4 tends to bring wetter conditions for the much of the Maritime Continent, and Phases 6 and 7 tend to bring drier conditions for the western Maritime Continent. Phases 5 tends to bring a mix of wetter and drier conditions.



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 El Niño conditions persisted over the equatorial Pacific during January 2024. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) continue to show El Niño conditions, with key atmospheric indicators (cloudiness and trade winds) still supporting these conditions but started to weaken. The positive Indian Ocean Dipole event has likely ended. El Niño events tend to bring drier and warmer-than-average conditions to much of the Maritime Continent during December – February.