Weekly Tropical Climate Note

High temperatures likely as Madden–Julian Oscillation strengthens

Over the past week the Madden–Julian Oscillation (MJO) has strengthened over the Australian longitudes. At this time of year, this means the MJO is likely to increase temperatures across the Top End, and generally, tropical northwest Australia. The MJO is one possible factor contributing to severe heatwave conditions that are likely to affect the Top End region and the Kimberley District in Western Australia this week; see the Bureau's heatwave service for more information http://www.bom.gov.au/australia/heatwave/.

At this time of year, a strong MJO in Australian longitudes can increase the chance of above normal rainfall over southern Queensland and New South Wales. For tropical northern Australia, the MJO influence on rainfall is still about a week away. As the MJO moves east into the western Pacific—as it is forecast to do next week—the chance of rainfall will increase over the Top End and Cape York. The increased chance of rainfall will likely be welcomed by those in the Gulf of Carpentaria regions of the Northern Territory and Queensland that have not yet had any substantial rainfall following the end of the dry-season.

The MJO is usually associated with an increase in tropical convection. This is the case now, but at this time of year the increased activity is still sitting north of the equator and, this week, includes an active monsoon, typhoon Khanun (Odette) and tropical storm Lan. Active monsoon conditions stretch from the Bay of Bengal to the Philippine Sea. Typhoon Khanun (Odette) made landfall over southern China on Monday (16 October) and is expected to move over already-flood-battered northern Vietnam in the coming days. Tropical storm Lan has formed east of the Philippines and is forecast to track north toward southern Japan although it is unclear now if Lan will impact any landmass. This enhanced convection is expected to wane late next week as the MJO moves eastward over the Pacific Ocean.

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

Central Pacific Ocean cools

Sea surface temperatures (SSTs) in the eastern and central equatorial Pacific Ocean have resumed their cooling trend, which had stalled over the past few weeks. Overall, the SST pattern across the equatorial Pacific Ocean is indicative of an ENSO-neutral state, although the climate system is inching closer to a La Niña-like state. In addition to the SST trend, the Southern Oscillation Index (SOI) has bumped up a little over the last few days. The 30-day SOI value to 15 October was +9.5; sustained values greater than +8 are usually indicative of a La Niña state.

All international climate models surveyed by the Bureau suggest further cooling of the tropical Pacific Ocean is likely. Seven of the eight models suggest SSTs will cool to typical La Niña values during late 2017, and six maintain these values for long enough to be classified as a La Niña event. While it is not unprecedented, it is unusual for La Niña to form this late in the year. Historically, La Niña conditions in December have contributed to an early onset of the North Australian monsoon.

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

Product code: IDCKGEW000

Further information

(03) 9669 4057