Tropical Climate Update

Madden–Julian Oscillation in western Indian Ocean

A moderately strong pulse of the Madden–Julian Oscillation (MJO) is currently located in the western Indian Ocean. Climate models generally agree that this pulse will weaken prior to moving into the eastern Indian Ocean.

At this time of the year, an MJO pulse near the western Indian Ocean normally has no widespread influence on rainfall patterns across northern Australia, Papua New Guinea or most of Indonesia. However, an MJO pulse in this region may contribute to stronger than average easterly flow across parts of northern Australia, particularly across eastern parts.

Read more about the Madden–Julian Oscillation

Quiet northern hemisphere tropical cyclone season

The northern Pacific Ocean has observed well-below-average tropical cyclone activity, despite entering a climatologically favourable time of the year. The northwest Pacific Ocean, which typically sees the highest annual tropical cyclone activity across the globe, has not seen a tropical storm since Nuri, in the first half of June. There have been no typhoons (equivalent to Australian tropical cyclones of category 3 or higher intensity) in the region since Vongfong in mid-May. Including the northeast Pacific and northern Indian Ocean regions, it is the first time since reliable satellite measurements began (roughly 1966) that no typhoons have been observed during a period spanning 4 June to 13 July. The last typhoon-strength system in this broad region was Nisarga, which was active in the northern Indian Ocean in early June.

Using energy (Accumulated Cyclone Energy–ACE) as a metric of tropical cyclone activity, the northern Pacific Ocean has only seen about 20% of its normal yearly activity so far in 2020.

A weak tropical low has formed to the east of the Philippines, but the Japan Meteorological Agency, which has forecasting responsibility for systems in this area, considers there is only a small chance this low will intensify to tropical cyclone strength.

Early northern rainfall onset likely for Australia

The Bureau released its first issue of the Northern Rainfall Onset (NRO) forecast for season 2020–21 on 25 June. The forecast indicates that for much of northern Australia, the first significant rains in the lead-up to the northern wet season (officially, October to April) are likely to occur earlier than average. Rainfall onset here relates to the timing of the first 50 mm of rainfall observed after 1 September.

The next update will be released 16 July, with fortnightly updates continuing until the end of August.

Read more about the northern rainfall onset

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