Seasonal climate summary southern hemisphere (winter 2015): Mild winter over most of Australia as El Niño strengthens

Abstract

The climate is summarised for the austral winter season of 2015 with emphasis on the tropical Pacific region as well as rainfall and temperature over Australia. In the tropical Pacific, winter was dominated by a developing El Niño event; by June the Southern Oscillation Index had already exceeded El Niño thresholds for the second month running and sea surface temperatures had also passed key threshold levels as the tropical Pacific Ocean warmed rapidly. Several composite indices of El Niño such as the 5VAR and Multivariate ENSO Index (MEI) continued to rise as the winter months progressed, indicating an atmosphere and ocean that was building towards a strong event, with index values by August being comparable to the previously strong El Niño events of 1982-83 and 1997-98. August saw the start of the strongest positive Indian Ocean Dipole event since 2006 while the Southern Annular Mode was consistently positive throughout winter. Australian rainfall was lower than average during winter, most notably over the southern regions, with daytime temperatures above normal in northern and western parts of Australia. Night-time temperatures were overall warmer than normal with the main exception being Tasmania, parts of the southeast and Northern Territory.