Circulation patterns are reviewed for southern hemisphere winter (June - August) 2004, with particular emphasis given to the tropical Pacific Ocean and the Australian region. Some El Niño indicators strengthened during winter 2004, reviving speculation about the return of a warm event. However, not all indicators supported this development. Values of the Southern Oscillation Index (SOI) andMultivariate ENSO Index were consistent with those of a borderline El Niño event throughout winter. However, outgoing long wave radiation (OLR) did not indicate a shift of convection toward the date-line, nor did upper and lower-level wind anomalies over the tropical Pacific suggest a broadscale suppression of the equatorial Walker circulation. Significantly warmer than normal waters persisted across the central tropical Pacific during winter but the classic El Niño warm tongue in the far eastern equatorial Pacific did not eventuate. Subsurface analyses across the equatorial Pacific showed a gradual contraction of cool anomalies east of the date-line and corresponding eastward progression of warm subsurface anomalies throughout winter. However the magnitude of these anomalies appeared to peak during July. Despite this, some national climate services declared an El Niño event by the end of August. This declaration was not supported by Australia’s National Climate Centre, highlighting differences between definitions used and priorities placed on indicators. Nevertheless, speculation that another El Niño-related drought was on the way forAustralia increased during winter, especially in Queensland. This speculation was fuelled by winter rainfall patterns which resulted in much of Queensland and northeast and coastal New South Wales (NSW) recording very much below average rainfall for the season. Wintermean maximum temperatures in parts of these regions were the highest since at least 1950.
D.A. Collins (Wed,) studied this question.