The BOM predicted that the La Niña pattern will persist into early 2021, and waters north of Australia and the Southwestern Pacific Ocean will be warmer than average in the coming three months.

[5] During mid to late November 2020, a moderate strength pulse of the Madden–Julian Oscillation (MJO) tracked eastwards across the equatorial Indian Ocean towards the Maritime Continent and Australian longitudes.

[6][7] On 24 November, the Bureau of Meteorology (BOM) reported that a tropical low had developed within a trough in the far northwestern corner of the Australian region, located approximately 860 km (530 mi) northwest of the Cocos Islands.

[10] The Joint Typhoon Warning Center (JTWC) assessed environmental conditions as being only marginally conducive for tropical cyclogenesis, with good poleward outflow and sea surface temperatures near 30 °C (86 °F) being offset by the effects of moderate vertical wind shear.

[19] Satellite scatterometer data revealed maximum sustained winds of approximately 45 km/h (30 mph) at 02:30 UTC on 30 November, a few hours prior to the system exiting the Australian region.

[25] On 6 December, the Bureau of Meteorology (BOM) reported that a tropical low had developed within a monsoon trough near the western end of Java, approximately 200 km (120 mi) north-northeast of Christmas Island.

[28][29] On 7 December, warm sea surface temperatures and strong diffluence in the upper troposphere fuelled the development of deep convection around the system's low-level circulation centre.

[30][31] Deep convection continued to develop near the centre during the overnight period, and as the low began to track eastwards, the JTWC upgraded the system to a tropical storm on the Saffir–Simpson hurricane wind scale at 18:00 UTC on 8 December.

[44][47] The presence of the Madden–Julian Oscillation and an equatorial Rossby wave in the Australian region contributed to the formation of another broad low-pressure system in the monsoon trough over the far eastern Indian Ocean during early December.

By late on 7 December, infrared satellite imagery indicated an improvement in the structure of the low, with the system displaying an increase in flaring deep convection, accompanied by rotation evident in the lower troposphere.

[50] Owing to the increase in organisation, the Bureau of Meteorology (BOM) classified the system as a tropical low by 21:00 UTC,[51] when it was located approximately 330 km (210 mi) northwest of Broome.

[50] Due to the system's proximity to the coast, however, both the BOM and the Joint Typhoon Warning Center (JTWC) forecast only a low chance of development into a tropical cyclone before making landfall.

[48][50] As the tropical low tracked southeastwards towards the coast, environmental conditions continued to improve, with sea surface temperatures nearing 31 °C (88 °F) and the system maintaining a robust poleward outflow channel in the upper troposphere.

[75][76][77][78] During mid December, favourable conditions from a pulse of the Madden–Julian Oscillation (MJO) located over the eastern Maritime Continent contributed to the re-formation of the monsoon trough over northern Australia.

[81] Environmental conditions were favourable for tropical cyclogenesis, with low to moderate vertical wind shear, good upper-level outflow and very warm sea surface temperatures nearing 31 °C (88 °F).

[83] Despite this, the tropical low's close proximity to land hindered intensification, and only limited development occurred before the system made landfall on 19 December near the Cambridge Gulf, between Wyndham and Kalumburu.

Despite tracking over land, the tropical low showed signs of organisation, with the generally favourable atmospheric conditions allowing the development of formative convective banding in the system's southern semicircle.

[96] Initially situated approximately 825 km (513 mi) west-northwest of the Cocos Islands, the system was located in an environment that was generally unfavourable for intensification, with moderate to strong vertical wind shear offsetting otherwise conducive upper-level outflow and warm sea surface temperatures of 28–29 °C (82–84 °F).

[98] On 1 January, the Bureau of Meteorology (BOM) reported that a tropical low had formed near Groote Eylandt in the western Gulf of Carpentaria, located about 635 km (395 mi) east-southeast of Darwin.

[100] Environmental conditions were assessed as being favourable for tropical cyclogenesis, characterised by very warm sea surface temperatures of up to 31 °C (88 °F), low to moderate vertical wind shear and an established poleward outflow channels in the upper levels.

[101] Flaring convection began to develop around the consolidating low-level circulation centre as the system tracked southeastward over the Gulf of Carpentaria, and at 00:00 UTC on 2 January, the BOM issued a tropical cyclone watch for parts of the northwestern Queensland coast.

[100] By 18:00 UTC, vertical wind shear values had decreased further as the tropical low moved underneath an upper-level ridge; however, despite the highly favourable environmental conditions, intensification was limited somewhat by the broad and elongated nature of the low-level circulation center.

[112] Despite the centre of the system tracking over land, Imogen maintained its organisation for several hours, assisted by the flat terrain that had been saturated by heavy rainfall generated by the cyclone itself.

On 5 January, the Bureau of Meteorology (BOM) reported that a weak tropical low had formed within a trough over the eastern Indian Ocean, centred approximately 500 km (310 mi) northeast of the Cocos Islands.

[115][116] Environmental conditions were assessed by the BOM as being unfavourable for significant intensification of the low, citing in particular the strong easterly winds in the upper troposphere that were forecast to develop by 10 January.

[117][119] On 9 January, the Joint Typhoon Warning Center (JTWC) reported the development of formative convective rainbands wrapping into the tropical low's centre, and determined that environmental conditions were favourable for the system to strengthen, in contrast with the BOM's assessment.

[167] The low drifted close to the coast of Timor very slowly with persistent spiraling bands of convection occupying the storm's circulation, producing prolific rainfall in the surrounding regions on 3–4 April.

[10] Although there were fluctuations in central convection, a favorable environment of deep moisture, low vertical wind shear, and good outflow meant further development of the system was expected.

[43] Seroja held this strength for roughly 12 hours before unexpectedly weakening to a Category 1 tropical cyclone yet again on 6 April, due to southeasterly wind shear and dry air partially exposing the low level circulation (LLC) and degrading its thunderstorm activity.

[175] Seroja resumed intensification by the next day, re-intensifying into a Category 2 tropical cyclone at 13:16 UTC on 9 April, as the storm began to weaken and absorb Odette, and wind shear started to ease off.