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Subseasonal Weather Outlook and Review

Review of Regional Weather for October 2022

 

1. Overview

1.1 During October 2022, much of the ASEAN region experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over northern Philippines (due to Tropical Storm Nalgae which made landfall in end-October), based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). In contrast to the above-average rainfall, northwest Mainland Southeast Asia experienced near- to above-average rainfall, while parts of northern Viet Nam and Papua experienced below- to near-average rainfall. The two datasets agree well over most of the ASEAN region. However, there are some discrepancies over parts of the western Maritime Continent, Borneo and southern Viet Nam, where GSMaP-NRT recorded near- to above-average rainfall whereas CMORPH-Blended recorded a mix of below- to above-average rainfall.

1.2 The observed rainfall anomaly pattern of above-average rainfall for much of the Maritime Continent region is broadly consistent with the predictions from the subseasonal weather outlooks for October 2022 (3 – 16 October and 17 – 30 October). Overall, much of Mainland Southeast Asia experienced near- to above-average rainfall for October. The subseasonal outlooks predicted drier conditions over western and central Mainland Southeast Asia for middle of the October. The observed anomalies also supported this with lower rainfall anomalies compared to the rest of the region.

era5_rainfall_anomalies
cmorph_bld_rainfall_anomalies
Figure 1: Rainfall anomalies for October 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 The northwestern and eastern parts of the ASEAN region experienced above-average temperatures during October 2022, with below- to near-average temperatures elsewhere (Figure 2). The warmest anomalies were recorded around Papua, with the coolest anomalies over parts of southern Sumatra, southern Borneo and eastern Java. Most of the cooler anomalies occurred for areas that also experienced above-average rainfall.

era5_temperature_anomalies

 

Figure 2: Temperature anomalies for October 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 There was no discernible Madden-Julian Oscillation (MJO) signal in the first week of October, based on the RMM Index (Figure 3). An MJO signal emerged over the Western Pacific (Phase 6) and propagated eastward to Phase 7 in the second week of October. This signal then maintained its strength and remained in Phase 7 for the rest of the October. Typically, during this time of the year, Phase 6 tends to bring wetter conditions for eastern Maritime Continent while Phase 7 tends to bring drier conditions for the western Maritime Continent.

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 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 remain consistent with La Niña conditions. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during the September to November period. Over the Indian Ocean, a negative Indian Ocean Dipole (IOD) was present. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.