Island Climate Update 212 - May 2018
Weak La Niña conditions transitioned to ENSO-neutral in the tropical Pacific during April 2018. Sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean remained below normal during April 2018, but continued to weaken relative to March values. The NINO3.4 index remains weakly negative at -0.33°C (was -0.61°C last month).
In the subsurface ocean (within the first 150 metres of the ocean), positive temperature anomalies shifted east of 140°W during the month of April and now extend across most of the equatorial Pacific. Significant positive anomalies (> +3°C) have now persisted in the central Pacific basin (170-160°W), centred at about 150m depth, for the second consecutive month. The only subsurface region exhibiting cooler than average temperatures was confined to areas around and east of 100°W.
The Southern Oscillation Index (SOI) has shown considerable variability since the beginning of the year, and is currently on the La Niña side of neutral, with a value of +0.5 for April 2018. April 2018 rainfall and convection anomalies in the tropical Pacific changed significantly, especially in the western Equatorial Pacific, where anomalously wet conditions in March gave way to anomalously dry conditions in April.
In summary, with the significant shift in rainfall patterns over the western equatorial Pacific and Maritime Continent, combined with the warming of equatorial waters, particularly in the subsurface and east of the Date Line, ENSO-neutral is expected to continue over the next few months: the international consensus is for ENSO-neutral conditions over the next 3 month period (75% chance over May – July 2018). The forecast models favor El Niño conditions emerging during spring (53% chance in September –November 2018).
Download the report: Island Climate Update May 2018 [2.5MB PDF]