Seasonal climate summary southern hemisphere (autumn 1998): decline of a warm episode (El Niño)

Southern hemisphere circulation patterns and anomalies for autumn (March-May) 1998 are reviewed, with emphasis given to Pacific basin climate indicators and Australian rainfall and temperature patterns. The El Niño event that had reached maturity over summer continued into autumn. However, the first real indications that the event was in decline emerged during autumn and by the end of May it was apparent that the end of the event was imminent. Indeed, the considerable extent of anomalously cold subsurface temperatures across the central equatorial Pacific suggested a rapid transition towards a positive phase of the Southern Oscillation (La Niña). While El Niño influences were evident across Australia during autumn, positive Indian ocean temperature anomalies favoured development of northwest cloudbands that delivered above average rainfall over much of the continent in April.