The world's weather patterns are slowly grinding towards a new El Nino event. The United States already acknowledges it exists while the Australian Bureau of Meteorology says there is a 70 per cent chance of it developing in the coming months, based partially on the fact that sea surface temperatures remain warm in the western tropical Pacific which, in turn, has meant that the south east trades have not yet dropped off to the extent normally expected in ah El Nino event.
Central and eastern Pacific SSTs already exceed El Nino thresholds and most medium-term modelling indicates that SSTs in the area will continue to exceed El Nino levels until at least the start of summer.
In terms of atmospheric indicators, recent values of the Southern Oscillation Index have risen back to neutral levels, with the 30-day SOI at around +2 at the moment, which is another reason that the bureau has yet to declare an El Nino.
As far as other atmospheric indicators are concerned, sustained changes in wind, cloud and broad-scale pressure patterns towards El Nino-like patterns have not yet developed, so the atmosphere is yet to join the SSTs in an El Nino event. In addition, as mentioned last week, large areas of Australia remain surrounded by above average SSTs, especially around northern and eastern Australia. This is providing a scenario rarely seen with developing El Nino events. Nevertheless, there remains a high degree of confidence that a full El Nino is likely in the coming months but there is a chance we could still see an El Nino event that is a little moderated by the warmer SSTs in the western Pacific.
To the west, the Indian Ocean Dipole is still neutral. All models suggest a positive IOD is likely to develop in the coming months but this is yet to happen. When it develops, in the second half of winter and early spring, it will reduce the number of northwest cloud bands crossing the continent. Such decreased cloud cover will favour warmer, above average maximums occurring from August onwards, but clearer skies in late winter will also result in below average minimum temperatures and could see a slight increase in late season frosts in some areas,
Finally, to the south in the Southern Annular mode is fluctuating around neutral to negative. While a neutral SAM has minimal effect, a negative SAM in winter can temporarily increase showers in Victoria and southern NSW and decrease rain along the east coast. A negative winter SAM is also good news for ski enthusiasts.
