ENSO & SST

ENSO and Sea Surface Temperatures

The tropical Pacific Ocean remains in a weak El Niño state, but there was a late surge of atmosphere-ocean coupling in February, resulting in large (probably short-term) changes in a number of indicators. The Southern Oscillation Index dropped dramatically from near zero in January to about -3 in February, when Tahiti recorded its lowest February monthly-mean sea level pressure, the lowest February value on record. Strong westerly zonal wind anomalies are evident in the west Equatorial Pacific. There is strongly suppressed convection over Australian longitudes and enhanced convection near the Date Line, and a clear northeastward movement and strengthening in the SPCZ. Many of these features are probably associated with the recent tropical cyclone activity in the Southwest Pacific.

A pulse of strongly positive temperature anomalies has developed in the subsurface across the central Equatorial Pacific, although sea surface temperatures remain relatively weak. The NINO3.4 average anomaly was about +0.3°C in February, having eased in recent weeks. NINO4 has weakened to near +0.8°C (from +1.2°C in January), and NINO3 has reduced from +0.6°C in January to near normal (zero anomaly) in February.

Despite recent events, almost all available models indicate the weak El Niño easing to neutral conditions (with positive NINO.4 anomalies) by May 2005, and over the winter. The chance of a La Niña developing is close to zero at present, and La Niña conditions are expected to remain very unlikely through much of 2005. However, it is likely that the region will continue to experience some El Niño-like climate conditions over the coming months.

Sea surface temperature anomalies (°C) for February 2005

Mean sea surface temperatures (°C) for February 2005