Please login to view this content.
12/08/2018, 4:39 pm EST

December 2018 ENSO Outlook

Weak-to-moderate traditional El Nino for the next 2-4 months Uncertainty on whether El Nino continues in 2019 Implications for Quarter 1 of 2019 climate implications are cold/snowy East U.S., stormy Western Europe and emerging wet pattern northeast Argentina Executive summary: The Climate Impact Company ENSO forecast for 2019 indicates with a high degree of confidence weak-to-moderate traditional El Nino through March of 2019. El Nino Modoki is less likely to occur. For quarter 2 of 2019 ENSO analogs favor El Nino continuing by 3 to 2. El Nino is favored 3 to 2 over returning La Nina for the last 5 months of 2019. The more recent analogs favor a 2019 descent to La Nina as subsurface ocean heat to fuel El Nino fades fast. There are many important climate implications featured in updated global climate forecasts for 2019 issued shortly by Climate Impact Company. The more confident forecasts for quarter 1 of 2019 is colder and snowy in the East U.S., very stormy Western Europe helping to ease the drought and an emerging wet pattern for northeast Argentina and southeast Brazil. Observation discussion: A conventional El Nino is underway and slowly the atmosphere is coupling with the equatorial East Pacific warming. The Pacific decadal oscillation (PDO) is trending toward the warm phase but not there yet. History has shown El Nino is stronger when +PDO is present. The positive phase of the Indian Ocean Dipole (+IOD) is a Southeast Asia/Australia drought producer but is expected to fade. Fig. 1: The daily global SSTA analysis and key regional features. Two HUGE issues have been associated with the slowly developing El Nino during late 2018: 1. An El Nino Modoki? 2. Coupling with the atmosphere. While the 2015-16 El Nino was one of the 3 strongest on record, El Nino events – in general – have been weaker than normal since the previous historic El Nino episode in 1997-98. The explanation for this ENSO intensity change was initially related to a change in the long-term cycle of the PDO flipping from a tendency of warm to cool phase. More recently the tendency for widespread anomalous warm ocean waters may be a reason why El Nino intensity itself has been suppressed. Fig. 2: Nino34 SSTA AND multivariate ENSO index have slowly but surely trended toward weak El Nino in 2018. Fig. 3: The El Nino Modoki index indicated a potential Modoki event earlier this year and as recently as August. However, Modoki is less likely now. El Nino Modoki may be a symptom of weaker El Nino events. Anomalous warmth in the equatorial region has a tendency to collect near the Dateline rather than the eastern equatorial Pacific biasing El Nino climate affects farther westward. An example would be instead of widespread anomalous warmth across the U.S. as with conventional El Nino the warmth is biased toward the West and the East is colder (as observed winter 2002-03. El Nino Modoki appeared to be developing earlier this year but that risk has lowered in recent months (Fig. 2). The atmosphere has been SLOW to couple with the warming in the eastern equatorial Pacific (Fig. 3). Only recently has the multivariate ENSO index (MEI) identified an El Nino-like climate STARTING to develop. Of course, upper ocean heat is the fuel source for any El Nino episode. East of the Dateline where El Nino forms upper ocean heat has been plentiful for much of 2018 (Fig. 4). The issue has been lack of an El Nino-like atmosphere to emerge to allow the warming to reach the surface. An ending to trade wind flow is necessary in this region to allow the surface warming and trade winds have been reluctant to dissipate completely. Interestingly, the most recent El Nino in 2015-16 which was very intense occurred with the requisite subsurface warming needed to drive warm ENSO. A weaker El Nino, more common during the past 20 years occurring in 2009-10 also occurred with buoyant subsurface warming of the East Pacific. Note that whether El Nino was strong or weaker the last two El Nino episodes witnessed the subsurface warmth needed to fuel El Nino fade rapidly in 2010 and 2016. Will that cool subsurface fade occur in 2019? Fig. 4: Upper ocean heat in the East Pacific to drive El Nino is similar to a previous strong (2015) and weaker (2009) El Nino episode. Note that both the strong and weak El Nino episodes lost the subsurface warmth to maintain El Nino in the second year. Forecast discussion: Dynamic and statistical models collected by the International Research Institute (IRI) for Climate and Society convey a consensus forecast extending a moderate El Nino into autumn 2019 (Fig. 5). The projected Nino34 SSTA for December is around or slightly higher than +1.0C. Interestingly, most models initiate the IRI chart warmer than +1.0C with a few which are cooler. However, the dynamic (red) and statistical (green) average Nino34 SSTA forecasts are initialized close to reality for December. The dynamic and statistical averages indicate a moderate El Nino into spring 2019 weakening but not ending next summer. If El Nino 2018-19 is weak the likelihood of a faster ending is likely. The 2015-16 and 2009-10 (recent) analogs certainly suggest that El Nino will end by next summer. The Climate Impact Company Nino34 SSTA forecast based on a 12-month retrogression to initialize the forecast identifies 2 scenarios (Fig. 6). There is general agreement on weak to moderate El Nino through the winter season. However, odds favor a lengthy El Nino over returning La Nina in 2019 by 3 to 2. The most recent analogs identify a short-term El Nino with La Nina returning by next summer. The continuing El Nino is based on distant past analogs. Forecast confidence is excellent through FEB/MAR and low for the following months in 2019. Fig. 5: A collection of dynamic and statistical Nino34 SSTA forecasts by the International Research Institute for Climate and Society to identify ENSO phase for 2019. Fig. 6: CIC ENSO analog forecast using Nino34 SSTA. Forecast implications: Let’s take a look at the CIC ENSO forecast implications on global climate for quarter 1 of 2019. They include a cold scenario in the Eastern U.S., stormy Western Europe, some beneficial rain for parts of the Australian drought and wet climate generating in northeast Argentina/southeast Brazil. North America: The more recent analogs favor a cold and stormy upper trough just off the East Coast extending toward Texas. The older analogs are colder and effect most of the U.S. while Canada is mild. Based on the analogs expected the updated climate outlooks for JAN/FEB/MAR 2019 to trend colder especially East. Europe: Both the older and more recent analogs are in full agreement on a stormy Western Europe weather pattern for quarter 1 of 2019. Heavy precipitation affects Western Europe extending inland to the Central/East-central Europe drought region. Relief is on the way for the European drought. Temperatures are likely above normal Southeast Europe and temperate elsewhere trending colder than normal Northeast Europe. Australia: Queensland to coastal Northern Australia is wetter than normal during quarter 1 of 2019. Western Australia is drier than normal. Expect some relief from tropical rains into the north and northeast portion of the Australian drought area. Marginally beneficial rains also affect coastal New South Wales. Hottest (anomalous) weather is most likely across Western and Southern Australia. South America: Both the older and more recent analogs whole-heartedly support wet weather for quarter 1 of 2019 across northeast Argentina to southeast Brazil while a widespread dry climate develops in Brazil.