Weekly Tropical Climate Note

Madden–Julian Oscillation moves over the Maritime Continent

The active convection of a Madden–Julian Oscillation (MJO) pulse moved across the Indian Ocean and into the Maritime Continent region during the last week. It has remained at moderate strength during the last fortnight, although most international climate models forecast the MJO to rapidly weaken in the coming days prior to reaching the western Pacific region.

When the MJO is over the Maritime Continent at this time of the year, cloudiness and rainfall is typically enhanced over Queensland and the Kimberley coastline in Western Australia. More significant rainfall associated with the passage of the MJO would typically be expected over locations further to Australia’s north.

See the Bureau's MJO Monitoring for current MJO information.

Widespread tropical activity over southern Asia

The passage of the MJO over the Indian Ocean coincided with onset of monsoon conditions over the Bay of Bengal. Also associated with the MJO was the formation of cyclonic storm Roanu, which initially developed north of Sri Lanka. The system then tracked northwards, remaining near to the east coast of India, before making landfall near the border of Bangladesh and Myanmar. Large rainfall totals were recorded as Roanu moved along India’s east coast and over southern Bangladesh’s low-lying Chittagong and Barisal regions, causing major flooding which led to fatalities and property damage.

In the northern Indian Ocean, widespread convection and rainfall currently extends from the monsoonal activity over the eastern side of the Bay of Bengal, across much of South East Asia and, most recently, into the northwestern Pacific Ocean. With the MJO over Maritime Continent longitudes the risk of tropical cyclone formation over the northwest Pacific Ocean is elevated this week. There is also a heightened tropical cyclone risk over the northern Bay of Bengal associated with the presence of an active monsoon trough.

The long-term means for tropical cyclone formation during May are 1.3 tropical storms (0.8 typhoons) for the western North Pacific Ocean, 1.0 for the South Pacific and southern Indian Oceans combined and 0.7 occurrences in the northern Indian Ocean, including the Bay of Bengal.

El Niño ends as tropical Pacific Ocean returns to neutral

Sea surface temperatures in the Pacific Ocean have returned to a neutral El Niño-Southern Oscillation (ENSO) state, with little chance of returning to El Niño levels. Model outlooks and current observations indicate there is at least a 50% likelihood of La Niña developing in the second half of 2016 – about double the normal chance. La Niña has little implication for tropical Australia during the dry season. However, La Niña is often, but not always, associated with above-average wet season rainfall over tropical northern Australia. La Niña is also associated with a more active tropical cyclone season with an earlier start to the cyclone season for Australia. The other possible outcome, ENSO-neutral (neither El Niño nor La Niña), does not necessarily mean average rainfall, as the influence from other climate drivers, such as the Indian Ocean Dipole, may be significant.

Very warm sea surface temperatures continue across waters off the northern Australia coastline. Warmth from this region is expected to contribute to above-average temperatures across northern Australia in the coming months.

See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.

Product code: IDCKGEW000

Further information

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