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Subseasonal Weather Outlook and Review

Review of Regional Weather for February 2023

 

1. Overview

1.1 During February 2023, a mix of below- to above-average rainfall was recorded over the Maritime Continent. The northern half of the Maritime Continent received predominantly near- to above-average rainfall, and the southern half received predominantly below-average rainfall although some above-average rainfall was recorded in the southern most parts (Figure 1). Over Mainland Southeast Asia, near-average rainfall was recorded over most of region. The largest positive anomalies (wetter conditions) were recorded over the Malay Peninsula for both the GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates. The largest negative anomalies (drier conditions) were recorded over parts of southern Sumatra and Sulawesi, 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 (with much of above-average rainfall in the northern Maritime Continent and below-average rainfall in the southern part) and near-average rainfall for Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for February 2023 (6 – 19 February 2023 and 20 February – 5 March 2023).

era5_rainfall_anomalies
cmorph_bld_rainfall_anomalies
Figure 1: Rainfall anomalies for February 2023 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2022. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

 

1.3 Warmer-than-average temperatures were recorded over northern Mainland Southeast Asia and parts of eastern Maritime Continent. Near- to below-average temperatures were observed over parts of southern Mainland Southeast Asia and around the Malay Peninsula. Elsewhere in the ASEAN region, near-average temperatures were observed. The warmest anomalies were recorded over northern Myanmar and northern Viet Nam, and the coolest over the southeastern Mainland Southeast Asia.

era5_temperature_anomalies

 

Figure 2: Temperature anomalies for February 2023 based on ERA-5 reanalysis. The climatological reference period is 2001-2022. 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 Indian Ocean (Phase 3) at the start of February. This MJO signal propagated eastwards through the Maritime Continent (Phases 4 and 5) in the first half of February and reached the Western Pacific (Phases 6 and 7) by the end of Week 2. The signal continued propagating eastwards before weakening from the middle of Week 3 over the Western Pacific (Phase 7) and becoming indiscernible at the end of the month, based on the RMM Index. Typically, during this time of the year, Phase 3 tends to bring wetter conditions to the western Maritime Continent, Phases 4 and 5 tends to bring wetter conditions to the Maritime Continent. Phase 6 tends to bring wetter conditions to eastern Maritime Continent while 7 tends to bring drier conditions to 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 La Niña conditions were present over the tropical Pacific but have weakened since December 2022. Although overall, sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean, continued to indicate 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.