El Nino Watch
Three letters = three consecutive months, by their initials. DJF = December-January-February; JJA = June-July-August.
Indices
ENSO indices and forecasts use overlapping 3-month seasons, named by the first letter of each month:
DJF, JFM, FMA, MAM, AMJ, MJJ, JJA, JAS, ASO, SON, OND, NDJ.
"Overlapping" means each season shares two months with the next one. So a value for JJA and a value for JAS are not independent: they share July and August.
Watch out: DJF starts in December of one year and ends in February of the next. "DJF 2027" in forecasts means December 2026 to February 2027.