Sea surface temperatures during the week of May 4, 2016, compared to the 1981-2010 average. A few pockets of cool water have appeared in the eastern tropical Pacific. There's a 75% chance that La Ni簽a will be in place by the fall of 2016, meaning sea surface temperatures in the central Pacific at the equator will be more than below average. It's possible the transition from El Ni簽o to La Ni簽a will be quick, with forecasters slightly favoring La Ni簽a developing this summer. Sea surface temperatures in the Nino3.4 region, our primary index for ENSO, have been cooling steadily since they peaked at 2.4簞C above average back in November. Recently, cooling has accelerated, and April was 1.2簞C above average using historically consistent sea surface temperature dataset from NOAA NCEI. There are 14 La Ni簽a events in our historical record, going back to 1950. (There are 23 El Ni簽o events in the same record). To qualify as a La Ni簽a event, the 3 month average sea surface temperature in the Ni簽o3.4 region must remain at least 0.5簞C below the long-term average for five or more overlapping 3 month periods.