El Niño is back

The Bureau of Meteorology’s El Niño-Southern Oscillation (ENSO) tracker has confirmed that El Niño thresholds have been reached in the tropical Pacific for the first time since March 2010.

ENSO indicators have shown a steady trend towards El Niño levels since the start of the year, with sea surface temperatures in the tropical Pacific Ocean exceeding El Niño thresholds for the past month. The climate model suggests El Niño is likely to develop over the coming one to two months, increasing the likelihood of drier conditions later this year.

The bureau’s assistant director for climate information services, Neil Plummer, explained that El Niño is often associated with below-average rainfall across eastern Australia in the second half of the year and warmer-than-average daytime temperatures over the southern half of the country. Western Tasmania and isolated parts of the tropical north have an increased chance of drier conditions, though May to July are currently likely to be wetter than normal over most of Australia. This is being driven by warmer than average Indian Ocean sea surface temperatures.

“The onset of El Niño in Australia in 2015 is a little earlier than usual,” Plummer noted. “Typically, El Niño events commence between June and November.

“Prolonged El Niño-like conditions have meant that some areas are more vulnerable to the impact of warmer temperatures and drier conditions.”

For May to July, warmer than normal days are likely over the tropical north, southeast and far southwest of Australia. Cooler than normal days are more likely in a large area from the northwest to central WA, extending across into western NSW. Nighttime temperatures for the season are likely to be warmer than normal over most of Australia, except in the northwest WA.

Plummer noted that while the El Niño is forecast to strengthen during winter, the strength of an El Niño does not necessarily correspond with its impact on Australian rainfall. Furthermore, while El Niño increases the risk of drought, it does not guarantee it; of the 26 El Niño events since 1900, 17 have resulted in widespread drought.

International climate models indicate that tropical Pacific Ocean temperatures are likely to remain above El Niño thresholds through the coming southern winter and at least into spring. El Niño is thus expected to become the dominant influence on Australian climate during the second half of the year.

To view the ENSO tracker, visit http://www.bom.gov.au/climate/enso/tracker/.