Review of Regional Weather for January 2022


1. Overview

1.1 During January 2022, the Maritime Continent experienced a mix of below- and above-average rainfall, with Mainland Southeast Asia experiencing its typical dry season, apart from northern Lao PDR and Viet Nam that experienced above-average rainfall (Figure 1). For the Maritime Continent, both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended) show large negative anomalies (drier conditions) over the Malay Peninsula and the southern half of the Philippines. However, there are some discrepancies between the two datasets elsewhere. CMORPH-Blended (Figure 1b) recorded below-average rainfall for much of the region, apart from the northern Philippines, and isolated parts of Sumatra and Borneo. GSMaP-NRT (Figure 1a) however, recorded more extensive areas of above-average rainfall with isolated areas of below-average rainfall primarily over parts of Borneo and Java.

1.2 The mix of below- and above-average rainfall for the Maritime Continent with no clear regional pattern is in line with the subseasonal weather outlooks for January 2022, which predicted a mix of below- to above-average rainfall depending on the outlook (27 December – 9 January, 10 – 23 January, and 24 January – 6 February), although the wetter conditions over northern Lao PDR and Viet Nam were not included in any of the outlooks.

Figure 1: Rainfall anomalies for the month of January 2022 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2021. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).


1.3 Near- to above-average temperature was recorded in Southeast Asia in January 2022, apart from northern Myanmar where below- to near-average temperature was recorded (Figure 2). The largest positive anomalies (more than 1°C warmer) were over central and eastern parts of Mainland Southeast Asia. For the Maritime Continent, the largest positive anomalies were over the Malay Peninsula (0.25°C – 1°C warmer), with the rest of the area near- or slightly above-average.



Figure 2: Temperature anomalies for the month of January 2022 based on ERA-5 reanalysis. The climatological reference period is 2001-2021. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).


2. Climate Drivers

2.1 A Madden-Julian Oscillation (MJO) signal was present over the Western Pacific (Phase 7) at the start of January 2022, based on the MJO phase diagram below (Figure 3). In the second week of January, the signal entered the Western Hemisphere (Phase 8) and then weakened rapidly. In the second half of January, there was no MJO signal. Phase 7 tends to bring drier conditions to the western Maritime Continent and expanding in Phase 8 to most of the Maritime Continent at this time of the year.



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 Over the tropical Pacific Ocean, La Niña conditions were present. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean were consistent with La Niña conditions. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during the December to February period.