June El Niño update: Damn the torpedoes, full speed ahead

It was not your imagination! Starting a couple of weeks ago, the Madden-Julian Oscillation (MJO) was in the phase that gave increased convection (cloudiness and thunderstorm activity) over the Indian Ocean, and that is a phase that tends to militate against El Nino. You are correct that the wind anomalies in both lower and upper atmophere, that have been showing a clear El Nino pattern, weakened in response to this MJO factor. The Southern Oscillation Index (SOI) became much more weakly negative than it had been just a few weeks earlier. Fortunately (if you like El Nino), the much heavier flywheel of the sea temperatures, both at and below the surface, do not change very quickly, so this latest "gunshot" against the event will not make much of a dent and undo what has been building up over the last several months. Furthermore, the MJO is predicted to change phase in the next week or so, so as to be less unfavorable to the El Nino, and maybe even favorable to it. When the MJO phase is in the central or eastern tropical Pacific, it helps support (or even strengthen) an El Nino. The MJO can weaken or strengthen an El Nino (or La Nina) when it stays in the same phase for a long time, such as over 1 month. But that rarely happens, as the MJO tends to propagate around the globe every 30-60 days or so.

Congratulations on noticing this very relevant, and likely relatively brief, interruption to the atmospheric patterns defining this El Nino.

You are correct that increased rainfall this winter in the Central Valley is questionable. The extended Pacific jet stream tends to bring increased rainfall to mainly southern California and the southwestern States (including snowpack as well as rainfall at lower elevations), so the San Juaquin Valley is in a better position to get good rainfall than the Sacramento Valley. Each event plays out differently, however, and we can't expect all events to bring the same patterns of rainfall departure from normal. I would say there is reason for hope for California this winter, especially late winter (Jan-Mar) with this developing El Nino that is already at moderate strength before mid-summer.

Again, I agree that analogues should not be used as the sole source of a real-time forecast, unless there is nothing else available. There is considerable uncertainty associated with the winter forecast for precipitation in California, but the tilt of the odds toward good results in the southern part of the state nonetheless exists, due to the expected extension of the Pacific jet stream even in the presence of climate change that may well be altering the usual jet patterns farther east in the US during winter.

In the strongest El Nino events, northern as well as southern Calif have received above average precipitation. In moderate El Nino events, central California may get good rains, but north of San Francisco the odds are not so good. The reason northern California is often left out of the forecast, is because it is in a transition zone between the region farther south that has the enhanced chance for above average precipitation (especially in late winter), and the region farther north (Oregon and Washington) that tend to be a bit drier than average during winter with El Nino. We're sorry, but that is what mother nature does, ON AVERAGE. In any particular case, it may or may not turn out this way, but over a large set of El Nino cases that is the tendency, based not only on empirical evidence (historical observations) but on dynamical (i.e. physical) modeling results where physical equations are used. As far as how strong the current El Nino may become by winter, it is somewhat up for grabs. At least a moderate event appears likely, but whether it will grow to become one of the very strong ones is unable to be resolved at this time. If it does become strong (with Nino3.4 and Nino3 index values of 1.5 or even 2 degrees C above average), central California will be in a better position to get a wet winter, and even farther north in California would have a decent shot at it. With the decadal climate possibly shifted from what it was between 1999 and early 2014, California also might stop having as bad a long-term drought situation. But we are not sure the decadal climate has shifted (I'm talking about the Pacific Decadal Oscillation, or PDO), since it needs to stay shifted for at least 2 or 3 years to be sure it is not just a 1 to 2 year break in the general 15-or-so year tendency. In any case, we hope California in general will get some relief from the drought, both from the El Nino and possibly from a shift of the PDO to positive phase after 1 to 2 decades in mainly negative phase. A lot going on here and it will be interesting to see the outcome! 

We don't see any evidence that "the blob" (the warm sea surface temperatures in the Gulf of Alaska) will impact this El Nino.  

During El Nino, the large scale pattern favors drier than average conditions over Central America and the Caribbean.  However, typical El Nino impacts are usually best seen in "seasonal" or an average of 3 months of data.  What you are pointing out appears to have been a significant, shorter-term weather event.  

Over the last 30 day average, here is the broader larger scale patttern as estimated by TRMM  (as of this posting, the dates are shown from June 9-July 8th 2015):

http://www.cpc.ncep.noaa.gov/products/fews/central_america/trmm_rainfal…

From this snap shot, most of the larger region is drier than average (i.e. consistent with El Nino).  But over Costa Rica, I see a wetter than average signal, which appaers to be mostly the exception rather than the rule.  

Overall, it is importat to realize that an El Nino does not guarantee impacts and there will be exceptions even during a stronger El Nino.  

Are you aware of a past archive for JMA forecasts/outlooks? I’ve looked for it before on the web and wasn’t able to find it. Therefore, it’s hard to compare forecasts with JMA so I can’t answer that part of your question... CPC has an archive of past outlooks here:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory… (click "Archive" link).

NOAA CPC/IRI declared El Nino in March 2015. It is our opinion that this is the start of El Nino irrespective of the ERSST dataset. This is because we do not declare ENSO events -- from month-to-month -- on the basis of a single index (or dataset) that is SST only (covered here: http://www.climate.gov/news-features/blogs/enso/why-are-there-so-many-e… and here: http://www.climate.gov/news-features/blogs/enso/decembers-enso-update-c…)

The Oceanic Nino Index (based on ERSST) is only one index to monitor ENSO and it is an simple way of classifying historical events and drawing comparisons. However, please always keep in mind that no index (or single dataset) is foolproof and ENSO is a *coupled* (meaning ocean + atmosphere) phenomenon, so for the weaker/borderline events in particular, we think it is important to consider other ENSO indices in addition to the SST based ones. In late 2014, we did not see a clear atmospheric response, so we did not declare an El Nino (http://www.climate.gov/news-features/blogs/enso/do-recent-global-precip…).

Since March 2015, we have seen both the tropical ocean and atmospheric indices aligned and more clearly exhibiting coupled behavior, which is why we have been calling it an El Nino. Also, our forecast probabilities for El Nino were fairly elevated (40-50%) prior to March (Feb forecast: http://iri.columbia.edu/our-expertise/climate/forecasts/enso/2015-Febru…), so we don't think it's accurate to say we never saw it coming.

A final (more minor point), recent values of the ONI will continue to change when the climatology changes. ONI values for 2014-15 will change slightly until the climatology becomes fixed in the year ~2030. More details here: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI…