The tropical Pacific remained in a neutral state (neither El Niño nor La Niña) in April 2013.
Since March, the slightly cooler than normal sea surface temperatures (SSTs) in the central and eastern equatorial region have eased. April SSTs were slightly warmer than normal along the Equator. The region of warmer (up to + 2°C) than normal SSTs that extended from Tasmania to New Zealand in previous months is still a prominent feature this month.
April NINO values estimates are 0.1°C for NINO3.4 , 0.2°C for NINO3 and 0°C for NINO4.
Higher than normal subsurface temperatures still exist along the Equator at about 150m depth west of the Dateline, while lower than normal temperatures are present east of the Dateline at similar depths. However these cold subsurface waters are overlain by a thin warm layer.
Oceanic integrated heat content anomalies (0–300 m) are currently close to zero all along the Equator but for the far western Pacific, where they are + 2°C.
The trade winds are currently slightly stronger than normal in the western Pacific, but remain within the normal range.
The South Pacific Convergence Zone (SPCZ) was positioned southwest of normal in April in the western Pacific.
The latest value for the TRMM ENSO index for the 30 days to May 5th is – 1.29 (on La Niña side of neutral) and the monthly SOI for April is 0.
The Madden – Julian Oscillation (MJO) was mostly inactive over the region in April. The MJO forecast indicates possible enhanced convective activity over the Maritime Continent mid-May.
The ensemble of dynamical and statistical climate forecast models that NIWA monitors indicates that neutral ENSO conditions are likely to persist over the May – July 2013 period, with 69 % chance, versus 24 % for La Niña and 7 % chance El Niño (percentages from the latest IRI/CPC statement).
