Borderline El Niño conditions still exist at present in the tropical Pacific. A noticeable change from July to August is the westward movement of the strongest positive sea surface temperature anomalies towards the central Pacific.
As a consequence, the NINO3 index in the eastern Pacific (150 °W to 90 °W) has dropped slightly, from + 1.2 °C in July to + 1.0 °C in August, while the NINO4 Index (160 °E to 150 °W) has increased from + 0.4 to + 0.8 °C.
Subsurface temperatures are still moderately above average in the upper ocean along the Equator, but according to the TAO analysis have weakened since July.
The atmospheric circulation has yet to show a typical El Niño pattern. The SOI is currently (in August) negative at – 0.7 but the low–level zonal winds are not very different from normal.
The TRMM ENSO index remains negative at – 0.2 for the 30 days to 1 September (values above +1.0 indicate El Niño conditions).
The OLR pattern across the equatorial Pacific still shows enhanced convection over the Maritime Continent north of the Equator, while convection was reduced north of the Equator east of the Dateline.
The SPCZ was not very well defined in August. A relatively strong MJO event moved into the tropical Indian Ocean in the last 10 days of August. It was forecast to be slowly–moving, and has in fact 'stalled' and weakened.
The international consensus is that the tropical Pacific is likely to warm further over the forecast season.
Nine of the 10 dynamical models that NIWA monitors indicate that El Niño thresholds will be exceeded during September to November 2012, with the remaining model indicating conditions on the warm side of neutral.
The coming event is likely to remain weak and short-lived, with a collapse of the event anticipated in the first quarter of 2013.
