GLOBAL MODELS SOUR ON POTENTIAL FOR EL NIÑO OVER NEXT SIX MONTHS, WEATHERTIGER MODEL GOES TRUE NEUTRAL THROUGH FALL…
- Currently, the equatorial Pacific remains in neutral ENSO conditions, showing neither a La Niña nor an El Niño state. Over the past month, the eastern Pacific has continued to cool and is now below normal, while the regions in the central Pacific that are used to define ENSO events have remained slightly warmer than average. Global weather patterns in May and early June remained mostly neutral overall.
- After calling for at least moderate El Niño to develop by the summer throughout the spring, dynamical models are still backpedaling in favor of projecting a continuation of warm-neutral conditions. This is a continued swing in the direction of WeatherTiger’s modeling, which has indicated neutral-positive conditions through fall for the last four months. WeatherTiger’s June modeling is cooler again showing solid neutral conditions through year’s end.
Current ENSO Conditions
The Pacific continued “waiting for Ninot” in May, as in the west, SST anomalies’ April warming stalled over the course of May as tropical easterlies re-intensified; the last weekly anomaly in the key Nino3.4 region is +0.4C, as opposed to a May average of about +0.6C. This is just above the threshold that, if these anomalies were maintained over a five-month period, would result in the declaration of an official El Niño event.
However, as seen below at left, the westerly wind anomalies that drove this warming period (yellow/red) have been replaced with anomalous easterlies (blue) later in May, which is associated with upwelling of cooler subsurface waters. At the same time, Nino1+2 region temperatures in the eastern Pacific continued to decrease in May as the easterlies were stronger than average there, retreating further from the very warm conditions observed in late winter and actually bringing the regional average SST anomaly to below normal as of this week.
The ocean/atmosphere system remained stuck in neutral between Niño and Niña, with the Southern Oscillation Index mostly positive over May, denoting more Niña-like conditions. Subsurface water temp anomalies continue to show a pool of cool water 75-150m below the surface in the central and eastern Pacific, with only weak anomalous warmth above that. Overall, subsurface warm water volume, which is strongly linked with future ENSO state at a lag time of three to nine months, remains near zero. In general, observations in May show no change occurring from a persistent neutral ENSO state.
ENSO Model Discussion
Dynamical models have continued to back away from even a weak Niño in runs released so far in June. The North American Multi-Model Ensemble, which averages the output of seven American and Canadian dynamical models, is significantly cooler in the June forecast run relative to the May data, which was itself much cooler than April. Rather than developing even a weak +ENSO event over the summer, the June NMME (at right) now suggests that there will be slight Nino3.4 region cooling into the fall, remaining steady through winter at around +0.25C. The most recent
CFS runs are even suggesting the possibility of weak Niña conditions arising over the late fall months, which remains remarkable as the CFS actually has a warm bias in ENSO forecasts. Finally, the June Euro Nino3.4 model, once suggesting a moderate or strong +ENSO, has finally thrown in the towel on El Niño ’17, the conclusion of a massive climbdown in expectations.
In summary, all models have shifted cooler once again in June, another major change in the dynamical modelling towards the summer/fall ENSO-neutral conditions that WeatherTiger’s ENSO Whisperer model has indicated for many months. For the first time in many months, consensus forecasting methodologies (at left) are no longer suggesting that El Niño is the most likely outcome at any point through early 2018.
ENSO Evolution Outlook
Overall, the passage of the “spring barrier” in ENSO prediction and the reversal of April’s modest observed warming in the past several weeks has further reduced the uncertainty in our outlook. With dynamical models further reducing chances of even a marginal El Niño, our forecast blends current trends, observations, and output from our own proprietary model of ENSO trajectory (the “ENSO Whisperer”). Output for the June run of the ENSO Whisperer is below, with the June model trending cooler than May’s at most months through the end of the year.
Our probabilistic assessment for June is that in two months (mid-August), there is a 70% chance of neutral conditions, 20% chance of El Niño, and 10% chance of La Niña. Further out, in four months (mid-October) there is a 5% chance of moderate/strong El Niño, 15% chance of weak El Niño, 60% chance of neutral, and a 20% chance of weak La Niña conditions in the equatorial Pacific. These confidence ranges are derived from real-time model errors. As shown above for October ENSO Whisperer predictions at a 4-month lead time, the model had a 48% reduction in out-of-sample forecast error relative to climatology.
ENSO impacts in the U.S. agricultural region this summer during growing season are likely to be muted. Some of the canonical wet/cool U.S. growing region pattern “ENSO signal” in the summer U.S. climatology is not driven by the ENSO pattern itself, but rather the change in the Pacific towards positive conditions driving wetter than normal weather via rapid SOI declines. With this tendency in decline, risks of warmer and drier conditions relative to normal are increasing in the U.S. growing region, particularly in the Plains; for more information, see our recent U.S. Summer Outlook.
Forecaster: Dr. Ryan Truchelut