Looking at the NWS' ONI (trimonthly 3.4 anomalies) website, I just noticed that the "current" version of the ONI definition has just been updated to use various 30 year periods vs. the prior 1971-2000 base period. Examples: ONI values during 1950-1955 will be based on the 1936-1965 base period, ONI values during 1956-1960 will be based on the 1941-1970 base period, and so on and so forth. What I hate about this is that this potentially introduces confusion as regards prior ONI based analyses of the various ENSO phases' correlations to things like US wx since this new table changes the ENSO phase of many seasons vs. what it was using 1971-2000. Examples: 1951-2 is a moderate Nino using the newest table vs. weak Nino when using 1971-2000. 1952-3, 1953-4, and 1958-9 are now all weak Nino's using new table vs. neutral using 1971-2000. There are many other changes. Since I've pretty much always used the 1971-2000 base ONI table, I could always choose to stick with 1971-2000 to remain consistent as long as it remains available. I'm leaning toward doing just that at least for now.
1971-2000 base ONI table: http://www.cpc.ncep....000_climo.shtml
Newest ONI table: http://www.cpc.ncep....ensoyears.shtml
Description of changes to base periods: http://www.cpc.ncep....NI_change.shtml
Yeah.. I don't much care for this update. We now have Nino/Nina events ( per TM ONI ) that were not there before because ala the numbers got bumped/changed and thus see 05-06 for one example. 51-52 on the old one was a very weak nino and is now a moderate Nino. Also now includes a multi year nino from 52-53 through 53-54.. And 58-59 is now listed as a Nino as well. 63-64 is now a border line strong Nino..