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Subseasonal Weather Outlook and Review

Review of Regional Weather for March 2023

 

1. Overview

1.1 During March 2023, a mix of below- to above-average rainfall was recorded over much of the Maritime Continent. Parts of the northern Maritime Continent, including Philippines and northeastern Borneo, received below- to near-average rainfall, while parts of the equatorial region received above-average rainfall. Over Mainland Southeast Asia, near-average rainfall was recorded over most of northwestern and eastern region, and below-normal elsewhere. The largest positive anomalies (wetter conditions) were recorded over the central parts of Borneo 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 in both CMORPH-Blended data and GSMaP-NRT data.

1.2 The observed rainfall anomaly pattern of a mix of below- to above-average rainfall for the Maritime Continent and below- to near-average rainfall for Mainland Southeast Asia are broadly consistent with the predictions from the subseasonal weather outlooks for March 2023 (6 – 19 March 2023 and 20 March – 2 April 2023).

era5_rainfall_anomalies
cmorph_bld_rainfall_anomalies
Figure 1: Rainfall anomalies for March 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 Below- to near-average temperatures were recorded over much of the western and central Maritime Continent, with above-average temperatures over parts of the eastern Maritime Continent. A mix of below- to above-average temperatures were recorded over the northern and central Mainland Southeast Asia and predominantly below-average temperatures were observed over southeastern Mainland Southeast Asia. The warmest anomalies were recorded over northern Viet Nam, and the coolest over the southeastern Mainland Southeast Asia.

era5_temperature_anomalies

 

Figure 2: Temperature anomalies for March 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 Western Pacific (Phase 6) at the start of March. This MJO signal propagated eastwards and strengthened as it passed through the Western Pacific (Phase 7) and Western Hemisphere (Phases 8 and 1) in the first half of March. In the second half of March, this signal relatively weakened and continued propagating eastwards through the Western Pacific (Phase 1) and Indian Ocean (Phases 2 and 3). The MJO signal weakened at the end of month and became indiscernible over the Maritime Continent (Phase 4), based on the RMM Index. Typically, during this time of the year, Phase 6 tends to bring wetter conditions to eastern Maritime Continent, while 7 and 8 tends to bring drier conditions to much of the Maritime Continent. Phases 1 and 2 tends to bring drier conditions over the eastern Maritime Continent, whereas Phase 3 tends to bring wetter conditions to the western Maritime Continent. Phase 4 usually brings wetter conditions to much of the 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 have now ended, and the tropical Pacific is now in an ENSO neutral state. Overall, sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric and oceanic indicators over the tropical Pacific Ocean, indicate neutral conditions.