El Niño/Southern Oscillation (ENSO)

The tropical Pacific Ocean remained in a neutral state (neither El Niño nor La Niña) in April 2014. However patterns of atmospheric and especially oceanic anomalies clearly indicate that an El Niño is currently developing.

Sea Surface Temperatures (SSTs) are now positive all along the Equator except for the far western Pacific (west of about 145°E). The latest monthly values for all NINO indices are consequently positive: 0.34°C for NINO3.4, 0.47°C for NINO3, and 0.5°C for NINO4.

Warm anomalies in the subsurface ocean have continued to propagate eastward and now exceed +5°C east of about 110°W at about 50m depth. Ocean heat content anomalies exceed +2°C over the same region.

The Intertropical Convergence Zone (ITCZ) was broader and more intense than normal east of about 155°E, while convective activity was reduced over the maritime continent.

Convection and rainfall in the South Pacific Convergence Zone (SPCZ) was reduced east of 165°E but intensified over the Solomon Islands and to the east of Papua New Guinea.

The latest value for the TRMM ENSO index for the 30 days to 4 May is 1.54 (indicating El Niño–like precipitation anomalies), however the Southern Oscillation Index (SOI) is positive (+1) for April 2014. The Madden – Julian Oscillation (MJO) has been mostly inactive in the last two weeks, and the forecasts indicate reduced intra-seasonal convective activity associated with the MJO over the next two

The consensus forecast from IRI / CPC indicates that neutral ENSO conditions are the most likely outcome (64 % chance) over the May – July 2014 period, however the chances of El Niño thresholds being crossed over the same period reach 45%. Chances for El Niño increases over the following seasons to each 66% in November - January 2014/15.





Surface temperature anomalies (ºC) for April 2014, data is from the NOAA OISST Version 2 dataset, available at the NOAA’s Climate Data Center (ftp://ftp.cdc.noaa.gov/Datasets/noaa.oisst.v2.highres/).