Computer models used by Australian Bureau of Meteorology (BoM) suggest that the emergence of the expected El Nino Pacific Ocean warming event is becoming less likely.
Only three of the eight computer models surveyed by BoM indicate the possibility of ocean conditions reaching El Nino thresholds by the middle of the southern hemisphere summer, with the remainder favouring persistence of neutral conditions, according to the latest summary of the prospects for a potential El Nino issued by BoM today (Tuesday, 21 October, 2014).
This compares with the situation just two weeks ago in the previous BoM report (issued on 7 October, 2014) when six of the eight models indicated the possibility of ocean conditions nearing El Nino thresholds by early southern hemisphere summer.
BoM reports that indicators for the so called El Nino–Southern Oscillation (ENSO), the cyclic system of warming and cooling seen in the Pacific Ocean, as well as patterns of Australian rainfall, “continue to show some El Nino-like signatures, but they remain in the neutral range”.
In particular, the tropical Pacific Ocean has remained warmer than average for more than six months and the Southern Oscillation Index (SOI) – a key indicator used by El Nino watchers that measures the atmospheric pressure difference between the island of Tahiti and Darwin in Australia – has remained negative since early June, both of which are consistent with the emergence of El Nino conditions.
However, BoM reports that neither ocean temperatures nor the SOI has reached typical El Nino levels for any sustained period. The key to the appearance of an El Nino is the strong interaction, or coupling, between the atmospheric system measured by the SOI and the warm waters of the Pacific Ocean whereby the two reinforce each other, but BoM reports that only weak atmosphere-ocean coupling appears to have taken place so far.
BoM appears to be less confident that an El Nino is appearing than the US National Oceanic and Atmospheric Administration (NOAA) which reported on 9 October that models continued to forecast at least a 60 percent probability that an El Nino will develop by the end of the year.