BOM: El Niño slowly weakening

16 Feb 2016

The 2015–16 El Niño continues its gradual decline. Sea surface temperatures in the tropical Pacific Ocean are cooling, and beneath the surface, cooler-than-average waters are advancing into the eastern Pacific. The atmosphere is also showing some signs of a declining El Niño. Trade winds are now the strongest they have been in nearly two years, though may weaken again briefly in the coming fortnight.

Based on the 26 El Niño events since 1900, around 50% have been followed by a neutral year, and 40% have been followed by La Niña. International climate models suggest neutral is most likely for the second half of the year. However, La Niña in 2016 cannot be ruled out, and a repeat El Niño appears unlikely. Historically, the breakdown of strong El Niño events often brings above average rainfall to some—but not all—parts of Australia in the first half of the year.

The Indian Ocean Dipole has little influence on Australian climate between December and April. However, Indian Ocean sea surface temperatures remain very warm across the majority of the basin which may provide extra moisture for rain systems across Australia. The southern hemisphere Indian Ocean remains at record warm levels, with January 2016 adding to the string of record warm months observed since mid-2015.

Indian Ocean Dipole

The Indian Ocean Dipole (IOD) is neutral. The Dipole Mode Index value to 14 February was −0.18 °C.

The IOD does not typically influence Australian climate during the months December to May. When the monsoon trough is in the southern hemisphere (as it typically is between the months of December to May) neither positive nor negative IOD events are able to form.

More generally, sea surface temperatures (SSTs) remain significantly warmer than average across most of the Indian Ocean basin, with a large part of the Indian Ocean measuring warmest on record for this time of year. This unusually warm ocean is likely to increase the available moisture for weather systems travelling across Australian in the coming weeks and months, increasing the likelihood of good falls occurring across southern Australia.

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Source: BOM