The warm SST east of 120W looked quite similar for both years. The reason why the "warming" this year did not lead to El Nino can be found by comparing the subsurface SST conditions for these cases: The thermocline was greatly depressed near the dateline by
Jan. 1997, typical during the onset of El Nino, while the thermocline tile (deep in the west, and shallow in the east) in
Jan. 2000 was enhanced, a condition in favor of stronger upwelling (therefore cooler SST) in the eastern equatorial Pacific. So, the question is what caused this warm SST east of 120W this past spring?
The local wind condition during
Apr. 2000 suggests
weaker easterlies, which brought
less equatorial upwelling, and possibly induced less latent heat loss. Of course, more infomation is needed to "blame" the wind for everything. Among other causes could be the local cloud coverage. An opposite situation is when the SST east of 120W is colder during April, as in
Apr. 1996; the local wind happened to be stronger, therefore in favor of stronger equatorial upwelling and colder SST. Just guessing.
Assuming it is the wind, then the question becomes:"What caused the wind anomalies there?" as Anna asked.
