Tropical Climate Update

Conditions for Australian monsoon onset remain unfavourable

Broadscale climate patterns across the Indo-Pacific region remain unfavourable for the onset of the Australian monsoon in the coming week. A weak monsoon trough currently a lies south of Indonesia, but it is not expected to strengthen significantly or reach the Australian coast in the next seven to ten days. The Australian monsoon is being kept at bay by a northern hemisphere near-equatorial trough and the absence of an active Madden–Julian Oscillation (MJO) pulse near the Maritime Continent. While a trough remains established in the northern hemisphere, cross-equatorial flow emanating from the South China Sea is unlikely to be of sufficient strength to drive monsoon trough development in the Australian region. The Australian monsoon onset can also occur when a tropical cyclone forms away from the Australian mainland but tracks over northern Australia, essentially dragging a monsoon trough into Australian latitudes. This second scenario is much less likely without an MJO in the region to promote tropical cyclone formation.

Related to the northern hemisphere near-equatorial trough was the formation of tropical storm Kai-Tak (Urduja) which passed over the northern Philippines in recent days, with reports of significant flooding. Kai-Tak (Urduja), which was briefly downgraded to a tropical depression, has re-strengthened to tropical storm intensity and continues to move westwards towards the southern Vietnam coast and the Malay Peninsula. For tropical cyclone information in this region please see the Japan Meteorological Agency webpage here.

Madden–Julian Oscillation over the Pacific Ocean

The Madden–Julian Oscillation (MJO) has returned to moderate strength over the eastern Pacific Ocean after briefly weakening in the region. Most climate models indicate the MJO will remain at moderate strength while tracking slowly eastwards in the coming week. At this time of year, when the MJO is over the eastern Pacific, below-average rainfall is typical across much of northern Australia and the Maritime Continent.

See the Bureau's current MJO monitoring for more information.

La Niña in the tropical Pacific Ocean

La Niña conditions persist in the tropical Pacific. Climate models suggest this La Niña will be weak and short-lived, persisting until early southern autumn 2018. Most oceanic and atmospheric indicators show clear signs of La Niña.

La Niña is typically associated with above-average rainfall during the northern wet season, average or above-average tropical cyclone numbers across the Australian region and an earlier onset of the Australian monsoon. However, this event is atypical in a number of aspects including its late development and influence on sea surface temperature across northern Australia. The current La Niña is also expected to be weak and short-lived, which typically means less influence upon the Australian tropics.

See the Bureau's current ENSO Wrap-Up for more information.