[computer model forecasts courtesy International Research Institute at Columbia University]
Summary El Nino, which refers to warmer-than-normal waters in the central and eastern tropical Pacific Ocean, can have an important effect on global weather patterns; especially, if it develops into what is commonly referred to as a “super” El Nino. In fact, we have had “super” El Nino’s in the tropical Pacific Ocean in the not too distant past (e.g., 1997-1998, 1982-1983) which caused global temperatures to spike to well above normal levels for a sustained period of time. Indeed, there are numerous signs that an El Nino is likely to develop this summer in the tropical Pacific Ocean and continue into the fall season and it is likely to have an impact on the upcoming tropical season in the Atlantic Basin. Many are suggesting that this potential El Nino will evolve into a “super” El Nino; however, I believe the odds are against that and I provide some of the reasoning in this discussion and also in the video (below).
Reasoning against a "super" El Nino Several dynamical computer forecast models tend to develop an El Nino during the summer months in the tropical Pacific Ocean, but then project it to level out or even weaken as we approach the late fall and upcoming winter season. One model in particular that I track from Japan called the JAMSTEC has a pretty good track record with respect to El Nino forecasting and while it does predict an El Nino to develop during the summer months and continues it through the fall season, it then tends to weaken it heading into the upcoming winter season. Also, if one looks at the recent history of the “multivariate El Nino Southern Oscillation (ENSO) index”, it is generally the case that “super” El Nino’s tend to follow relatively warm periods with weak El Nino conditions in the tropical Pacific Ocean whereas weaker El Nino’s tend to follow relatively cold periods (i.e., La Nina conditions). The last few years have in fact been dominated by La Nina (cold) conditions in the tropical Pacific Ocean which is supporting evidence that a “super” El Nino is less likely to form. Finally, another important index that meteorologists track with regard to the state of the tropical Pacific Ocean is called the Southern Oscillation Index (SOI). This index gives an indication of the development and intensity of El Nino or La Nina events in the tropical Pacific Ocean and it is calculated using the pressure differences between Tahiti and Darwin. If there are negative values of the SOI then this can be indicative of upcoming El Nino episodes. A “long-lasting and sharply negative” SOI value can be a useful predictor of a very strong or “super” El Nino. Currently, the SOI values that we are observing are nowhere near the values experienced during or just preceding the “super” El Nino years of 1982-1983 and 1997-1998.
Potential winter implications One final note, the difference between a weak and “super” El Nino can be huge when it comes to impact on winter weather in the Northeast US. An ongoing “super” El Nino next winter would increase the odds of a warm winter in the Northeast US whereas a weaker El Nino - especially one based in the central tropical Pacific Ocean - can still allow for a cold and snowy winter (more on that outlook at a later time).