ENSO 2017/18

It seems the high ridging into the eastern seaboard is evident of La Ninas for the month of February.

https://twitter.com/weatherchannel/status/963183322913476609

A pool of warm water has formed to the east of the equatorial Pacific which will put a damper on the weak La Nina. The latest ENSO 3.4 anomaly is -1.1c below average which shows the Pacific is still within the La Nina signature or threshold. Increasing chances of ENSO neutral forming during Spring 2018 but still quite low at this stage, around 50-60% likely. It seems Dec-Jan-Feb's ENSO 3.4 anomaly will be within the La Nina threshold which means that we need one more tri-monthly period of equatorial Pacific SSTs to be at least -0.5c below average for a weak La Nina to be officially designated. In my opinion, this is a highly likely occurrence.



http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

Latest El Nino 3.4 anomaly is -0.7 which is within the weak La Nina threshold and I think we can say for certain now that 2017-18 was an official weak La Nina. We only have one week to go and it would take over a +2.0 anomaly to make it not a La Nina approximately, we all know that's impossible to do within over the space of a week. To think how it looked like we were going into an El Nino back in June 2017 was crazy then it completely flipped around in July. This is one of the latest developed ENSO events I've seen on record, even the incredibly weak La Nina of 2016-17 had developed in the Summer season and it ended on the last tri-monthly period (Oct-Nov-Dec) of 2016.

The latest NOAA SST chart on the 22nd March shows the ENSO region still firmly in a weak La Nina setup with the warm pool of SSTs that had been developing over to the eastern side of the equatorial Pacific in February continues to be an absence since the last update I gave here in the thread above.



However, if we look at the subsurface temperature anomalies, we can see quite an extensive and extreme warm pool developing just over to the western side of the equatorial Pacific. But if you look at the sea surface temperature anomaly chart above, that's where the coldest temperature anomalies are tending to be, they're like opposites of each other here. Usually, it takes a few weeks for the subsurface temperature anomalies to have an impact on the sea surface temperature anomalies so we should be seeing some warming of the equatorial Pacific soon.

Just remember one thng though that we're in the Spring unpredictability barrier which means it is literally impossible to say where ENSO will go in 2018-19. As we've seen from 2017, this barrier can sometimes carry on into the Summer too.



http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

Just for what it's worth, here's what the CFSv2 is showing though it's only just predicting this given the current situation in the equatorial Pacific. If you cast your mind back to this time last year, many of its ensemble members were going towards a strong or perhaps even very strong El Nino. The model sees us gradually going towards ENSO neutral in Autumn 2018.

The Jan-Feb-Mar ENSO figure is now in and NOAA has officially designated the weak La Nina for 2017/18. I'd like to note the similarities to 1995/96 which also had a weak La Nina, a mild January, a cold February, a delayed Spring including a cold and wet March and the coldest May on record. Not to mention, 1995/96 was part of the Winter 2017/18 analogues! Very intriguing, I will discuss this more in the Summer thread since this is the ENSO thread.