Analog Indicates The Uncertainty of ENSO 2020

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Highlight: A low confidence forecast; ENSO 2020 uncertain.

Executive Summary: Based on four consecutive months of Nino34 SSTA >+5.0C we are technically in weak El Nino right now and given the moderately warm SSTA near and east of the Dateline and borderline warmth to support El Nino in the subsurface eastern equatorial Pacific Ocean the weak El Nino could last another 1-3 months. Analogs and dynamic models all agree on neutral ENSO developing during quarter 2 of 2020. However, there is a WIDE range of ENSO phase possibilities for the second half of 2020 including a robust La Nina forecast by NCEP CFS V2. However, as indicated by the CIC analog, forecast confidence of ENSO phase for Q3 and Q4 of 2020 is extremely low.

Fig. 1: Climate Impact Company ENSO analog forecast for 2020 indicates a wide variety of possibilities implying low confidence.

Discussion: The last 4 months have produced Nino34 SSTA observations >0.50C which qualifies as a weak El Nino. So…does weak El Nino continue, weaken of flip to La Nina in 2020? The Climate Impact Company ENSO analog forecast clearly represents the low confidence of this forecast as prediction solutions range from El Nino to La Nina (Fig. 1) with a consensus forecast right-in-the-middle: Neutral ENSO.

Dynamic models indicate the same theme ranging from a developing La Nina during JUN/JUL/AUG which intensifies by next October according to the NCEP CFS V2 (Fig. 2) to borderline weak El Nino continuing another 1-3 months followed by neutral ENSO indicated by both the ECMWF (Fig. 3) and Australia Bureau of Meteorology (Fig. 4).

Currently, the eastern half of the equatorial Pacific indicates two ENSO regimes. Near the Dateline a full-blown El Nino-look is present with widespread moderately warm SSTA while in the eastern equatorial Pacific SSTA is neutral (Fig. 5). The ENSO look is reminiscent of El Nino Modoki. The subsurface warmth is borderline supportive of weak El Nino and has been since last October (Fig. 6).

Diagnostics support the short-term weak El Nino followed by neutral ENSO indicated by the CIC analog consensus forecast, Bureau of Meteorology and ECMWF outlooks. Right now there is no indication of a La Nina ahead as forecast by NCEP CFS V2.

Summary: A weak El Nino is in-place. The forecast is for weak El Nino to last another 1-3 months. The weak El Nino forecast is supported by marginal warmth in the subsurface which is persisting and weak-to-moderate warmth in the Nino4/Nino34 regions. The short-term weak El Nino is supported by both the ECMWF and Australia Bureau of Meteorology dynamic models. However, once quarter 2 of 2020 arrives ENSO should transition to neutral phase. During the second half of 2020 neutral ENSO has a 2-in-3 chance of continuing with a 1-in-3 chance of La Nina developing. Forecast confidence is low and attributing ENSO to climate forecasts should be applied sparingly. Regions of warm/cool SSTA emerging during quarter 2 of 2020 are likely a stronger predictor of climate versus ENSO.

Fig. 2-4: The NCEP CFS V2 ENSO outlook indicates La Nina by JUN/JUL/AUG followed by intensification into OCT (top left). The ECMWF forecast indicates borderline weak El Nino to neutral ENSO for 2020 (top right). The Australia Bureau of Meteorology ENSO outlook indicates short-term borderline El Nino followed by neutral ENSO in 2020.

Fig. 5: The weekly global SSTA analysis provided by NCDC/PSD indicates El Nino characteristics and neutral ENSO indications in the Pacific.

Fig. 6: Borderline upper ocean heat east of the Dateline to sustain a weak El Nino remains in-place.