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Subseasonal Weather Outlook and Review

Review of Regional Weather for November 2022

 

1. Overview

1.1 During November 2022, a mix of below- to above-average rainfall was recorded over the Maritime Continent, while near-average rainfall was recorded over much of Mainland Southeast Asia, except for southern and northeastern Mainland Southeast Asia where a mix of below- to above-average rainfall was recorded (Figure 1). The largest positive anomalies (wetter conditions) were recorded over southern Mainland Southeast Asia and central Borneo, for the GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates datasets respectively. The largest negative anomalies (drier conditions) were recorded over central Sumatra and northern half of the Philippines, with CMORPH-Blended data showing relatively drier anomalies as compared to GSMaP-NRT data.

1.2 The observed rainfall anomaly pattern of a mix of below- to above-average rainfall for the Maritime Continent and the above-average rainfall for southern Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for November 2022 (31 October – 13 November, 14 – 27 November and 28 November – 11 December), although the wetter condition over central Borneo was not included in any of the outlooks.

era5_rainfall_anomalies
cmorph_bld_rainfall_anomalies
Figure 1: Rainfall anomalies for November 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 Warmer-than-average temperatures were recorded over most of Southeast Asia north of 10°N, except for some northwesternmost parts of Mainland Southeast Asia where below- to near-average temperatures are observed. In contrast, below- to near-average temperatures were recorded for most of the regions south of 10°N during November 2022 (Figure 2), except for south-eastern parts of the Maritime Continent where above-average temperatures are observed. The warmest anomalies were recorded around northern Viet Nam, with the coolest anomalies over central parts of Java islands.

era5_temperature_anomalies

 

Figure 2: Temperature anomalies for November 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 An Madden-Julian Oscillation (MJO) signal was present over the Western Pacific and the Western Hemisphere (Phases 7 and 8) in the first week of November, however it weakened and became indiscernible by the second week, based on the RMM Index (Figure 3). At the beginning of the third week, an MJO signal emerged over the Maritime Continent (Phase 4), which strengthened and propagated eastwards towards the Western Pacific (Phase 7), before becoming weak again at the end of the month. Typically, during this time of the year, Phase 6 tends to bring wetter conditions for eastern Maritime Continent while Phases 7 and 8 tends to bring drier conditions for the western Maritime Continent. Also for November, Phases 4 and 5 bring wetter conditions to much of the Southeast Asia. Therefore, the MJO may have contributed to the wetter conditions over southern coastal parts of Mainland Southeast Asia and southeastern Maritime Continent region in November 2022.

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 La Niña conditions were present over the tropical Pacific. 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 Southeast Asia during the September to November period. Over the Indian Ocean, a negative Indian Ocean Dipole (IOD) was present and showing signs of weakening. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.