Sea surface temperature (SST) anomalies in the tropical Pacific continued to increase and expand eastward along the Equator during May 2015 and are currently showing a pattern consistent with weak El Niño conditions. The latest monthly anomaly values for the NINO SST indices are: +0.83°C for NINO3.4 (was +0.55°C in February), +0.87°C for NINO3 (was +0.26°C last month) and +1.07°C for NINO4 (was +1.05°C last month).
Subsurface ocean temperature anomalies in the Equatorial Pacific have also continued to intensify and propagate eastward. They now reach about +5°C around 130°W. Subsurface waters off the South American coast have warmed significantly and reach about +5°C at 50m depth. Positive upper ocean heat content anomalies (upper 300m of the Ocean) have intensified in the eastern Pacific Ocean and reach above +2°C between 140°W and 110°W. The Southern Oscillation Index (SOI) was slighty negative at about -0.3 in April 2015.
Convection and rainfall was suppressed in the western Equatorial Pacific and intensified in the central Pacific, a pattern consistent with El Niño conditions. The latest value for the TRMM ENSO index for the 30 days to 3 May is +0.78 (on the El Niño side of neutral). The Madden-Julian Oscillation (MJO) was active at the beginning of April 2015 but weakened toward the middle of the month. The Climate Prediction Centre (CPC) dynamical model (ensemble GFS) and the CPC statistical model both predict weak MJO activity over the western Pacific sector over the next two weeks. The consensus ENSO forecast from the IRI/CPC places the chance of conventional El Niño threshold being crossed over the May – July 2015 period at about 80%.
