El Niño / Southern Oscillation (ENSO)

The Tropical Pacific ocean is currently on the brink of El Niño, with a recent resumption of warming after a short-term dip in the sea surface temperatures (SST) indices.

The latest weekly NINO3.4 index indicates central–western equatorial Pacific ocean SSTs are now + 0.7 °C above average. Currently the NINO3 index in the eastern Pacific (150 °W to 90 °W) is the highest of the NINO indices with anomalies reaching + 1.1 °C.

Subsurface temperatures across the equatorial Pacific have risen to become moderately above average in the upper ocean from just east of the Dateline eastward to 90 °W, and also in the western Pacific to a lesser extent. However the atmosphere hasn't caught up yet with the ocean and doesn't display the typical characteristics associated with El Niño.

The SOI is back in the neutral range at +0.1 standard deviations after having been negative (– 1.2) in June. Westerly anomalies that were observed in the western Pacific in June have weakened recently. The TRMM ENSO index remains around – 0.8 for the 30 days to 29 July, which is still on the La Niña side of neutral.

The OLR pattern accross the equatorial Pacific still shows enhanced convection over the Maritime Continent, while convection is reduced north of the Equator east of the Dateline. The SPCZ was not well defined in July.

The MJO signal has been weak in the past few weeks and its current phase might be partly responsible for the lack of coupling between the ocean and the atmosphere. However 8 of the 10 dynamical models that NIWA monitors indicate that El Niño thresholds will be exceeded during the forecast period (August to October 2012) but the coming event might remain weak.