Based on https://climatereanalyzer.org/clim/sst_daily/?dm_id=nino3.4, 1988 is the year from the dataset with the lowest temperature throughout June and July.

I posted a comment earlier about how 1982-1983 (the start of the data) had a historically severe El Nino, and the comment got shadowbanned. I don't understand why that happens sometimes. Hasn't happened for months, but when it does it's always on innocuous factual comments, it's weird.