Melbourne, 19/5/2009
(BoM) The 30-day Southern Oscillation Index [SOI] to 9 May was -4. Contributing pressure anomalies were -0.2 hPa at Darwin and -0.7 hPa at Tahiti. The official monthly SOI for April was +9, and its 5-month running mean [centred on February] was also +9.
Most atmospheric indicators suggest neutral ENSO conditions. The SOI remained within one standard deviation from mid-March. Easterly low-level winds over the near-equatorial western Pacific Ocean remained weaker during the past few weeks. Westerly low-level wind anomalies have frequented the tropical eastern Indian Ocean over recent months. Cloudiness has been greater than normal about the Maritime Continent and less than normal about the near-equatorial date-line, for most of the previous several months. The central near-equatorial Pacific Ocean sea-surface temperatures [SST] showed a warming trend during recent weeks and are currently close to the long-term mean with a few patches of warm anomalies.
Most ENSO forecasting models show neutral ENSO conditions to continue during the next few months. Some recently run climate models suggest a further warming in the Pacific by the southern hemisphere's spring. See the Bureau's "ENSO Wrap-Up" at www.bom.gov.au/climate/enso/ which includes a compilation of ENSO dynamic model predictions.