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August 2015 El Niño update: Supercalifragilisticexpealidocious

As of August, NOAA and IRI forecasters are predicting this El Niño will peak in the late fall/early winter with 3-month-average sea surface temperatures in the Niño3.4 region near or exceeding 2.0°C (3.6°F) above normal. If this forecast comes true, it will place the 2015 event among the strongest El Niños in the (admittedly short) 1950-2015 historical record. What would this mean for expected impacts in the United States?

But first, this status update!

Sea surface temperature anomalies (departures from the long-term average) increased in much of the equatorial Pacific during July. The July average in the Niño3.4 region was +1.2°C above normal according to the ERSST monitoring datasets. The atmospheric features observed in the equatorial Pacific region during July show that the El Niño ocean-atmosphere coupling is cranking along: easterly winds near the surface were consistently weaker than normal, as were the westerly winds in the upper levels of the atmosphere, and satellites saw more clouds than average in the central and eastern Pacific.

The atmospheric response provides not just evidence that El Niño is strengthening, but confidence that it will continue to develop because the weakened near-surface easterly winds allow the surface waters to warm. Another near-surface westerly wind burst occurred in the western Pacific in late July, which will probably further reinforce the reservoir of warmer subsurface waters. The strongest El Niño events have all had very consistent near-surface wind anomalies across the tropical Pacific that lasted through the summer and fall.

How much does strength matter to El Niño impacts?

El Niño is a climate pattern located in the tropical Pacific, so it doesn’t affect U.S. weather directly. Rather, it changes the larger-scale flow or circulation of the atmosphere.  Warmer tropical Pacific waters release more heat to the atmosphere, causing more rising air and storminess in the central and eastern tropics. The rising air moves north (and south) away from the tropics, traveling to the mid-latitudes, where it shifts the North Pacific jet stream farther southward and eastward. Movement and extension of the jet stream can bring more storms to the United States, and change the seasonal temperature and precipitation patterns. For a great explanation of the way this works, check out Tony’s post.

The point of mentioning this is that there are a lot of complex mechanics behind how El Niño affects U. S. weather. There is a domino effect that arises from the warmer surface waters in the tropical Pacific, and small changes in how later dominos fall can ultimately determine exactly what will happen over the U.S.  While we have more confidence in general impacts over the U.S. in an El Niño because of the shifts in the jet stream, they’re not guaranteed, because the ultimate result will also depend on factors (chaos & other climate patterns) that are not predictable months in advance and can also impact the jet stream and large scale atmospheric flow.    

This is why we keep saying that El Niño “tilts the odds” for weather and climate impacts. For example, in any random non-ENSO year, the chances that southern California will receive above- normal, near-normal, or below-normal rainfall in winter (December – February) are equal: 33.3% above normal, 33.3% near normal, and 33.3% below normal. During a strong El Niño year, these odds might shift to, say, 60% chance of above, 30% chance of near normal, and 10% chance of below. (This is just an example, not an official forecast!)

In other words, even a strong El Niño is not a sure-fire drought-buster for California (Tom wrote about this last year; and Mike covered it as well), so it’s not time to stop conserving water, especially given how entrenched this drought is (i.e. it will likely take more than one good year to erase). However, a strong El Niño does increase the chance of more precipitation overall during the winter, and also brings the potential for extreme rainfall. This may help alleviate the drought, but also can also lead to mudslides and flooding.

So at the Climate Prediction Center we’re not spending a lot of time debating about if El Niño Bruce Lee will be the strongest El Niño in history, or the second-strongest, or the third, etc. A strong event increases the probability that the U.S. will experience weather and climate impacts, but the strength of the event does not map directly on to the strength of the impacts.  

Winter precipitation

Winter precipitation (December-February) in 1982-83 and 1965-66—two strong El Niño events—compared to the 1981-2010 average. The winter of 1982-83 showed the "classic" wet signal that El Niño often brings to California, but the winter of 1965-66 did not. Maps by NOAA Climate.gov, based on NCEI climate division data provided by the Physical Sciences Division at NOAA ESRL.

We have a relatively confident forecast for a strong event, and this provides long-range forecasters with information they can use to develop their seasonal forecasts. So, although there are no guarantees, the odds nonetheless really are tilted in specific directions in various parts of the U.S. as far as winter climate is concerned. A significant El Nino like this one provides an uncommon opportunity for people to anticipate the climate tendency well in advance of the main impact season.

Comments

Thank you for responding. May I suggest an entire post giving the scientific explanation for why El Ninos typically peak at the end of the year. If this is an active area of research, then tell us what the current thinking is. This is after all the ENSO blog. If the models predict a peaking of Nino3.4 in the late fall, early winter and past historical data shows this to be true, then what information is going into the models?

I was a bit hesitant at first to ask this question here because I'm not sure if it applies to ENSO, but I can't seem to find the answer anywhere else so here goes.. I've read a lot about the "period of uncertainty" (my paraphrase) in the northern hemisphere spring and how you have to get past that period to have the best possible chance of seeing a clear ENSO picture for the following fall/winter. When it comes to long range forecasting in general, is there also a period of uncertainty in the northern hemisphere autumn as well? Or is it only spring?

Thanks for this nice site, but I do have a bone to pick with you - when presenting potential effects of a "Strong" El Nino, 65-66 does not qualify as one, as for example, it ranks as having only the 7th lowest SOI value and the 9th warmest Nino 3.4 value (based on ERSSTv4 data) of all events since 1950. I rank this as a moderate event. My point is that if you are going to describe the potential effects of a strong El Nino, you need to limit that discussion to only those events, otherwise it is misleading - a lot of this is going around these days. The recent strong events were: 82-83 and 97-98 and perhaps 72-73, 91-92, and 57-58, depending on your method of classification. And as you know, only two of those were in the super category - 82-83 and 97-98 - these two deserve a special place for themselves and they both produced very similar effects across the Pacific. Comparing 82-83 to 65-66 is just not a good fit. It remains to be seen just how strong this event will get this year. It is trying to be strong and the model predictions of Nino 3.4 definitely show a very strong event, but we shall see.

Thanks for your comment. At the Climate Prediction Center, we use the Oceanic Nino Index (ONI) as the determination for the strength of the event. 

> 0.5C - Weak; >1.0C - Moderate; >1.5C - Strong

We do not have a super category.

We recognize that others may determine the strengths of El Nino events differently.

In reply to by CCRAB

ONI yes fine. Perhaps we need a super category, >2.0?, as clearly 82-83 and 97-98 dominated the Pacific in a similar manner. If we pick an analogy for the prediction of +2.0 ONI for the end of this year (not saying it necessarily will happen), I think these 2 past events make the most sense, as their max ONIs were +2.1 and +2.3 respectively...

In reply to by tom.diliberto

hello fellow readers - all those of you asking "what is going to be the effect of XYZ climate phenomenon in ABC location on PQR date" should slow down and reread the WHOLE post and ALL the comments. Because the short answer to your questions is "no one can know for certain." There are changes in the likelihood of certain events but as the authors point out (repeatedly and patiently) nearly opposite effects could occur as a result of ENSO because of the myriad interactions with other phenomena." Interestingly the forecast models don't currently show a strong precipitation signal for Northern California.

Hi weather gurus, Can you point me in the direction of any way to explain what's happening on Mexicos south pacific coast? We're dyin' here. Temps reaching 100, 80% humidity, and no rain! Where are our nightly thunderstorms? Forecasts will call for 80% chance of rain! then it evaporates. What happened to our hurricane season? It started early and then stalled. The few that are forming seem to be forming west of us, leaving us in the (dry) lurch. Is this related to the El Niño pattern? Cause there'll be no Diwali here, either, if we don't get our rain.. Thanks for all the cool stuff you do! Regards, Steaming in Zihuatanjeo

Does the 11 year solar cycle have much effect on El Ninos ?

My parents are on a cliff in Dana Point, Ca and I am in Northern Ca I need to know how we will be affected when this hits and how long is it going to rain for? Sorry I don't understand all the mumbo jumbo technical science terms so if someone could explain in English that would be helpful.

I am planning a very expensive Galapagos cruise Easter week. I will be taking two children ages 10 and 12. How will El Nino impact the environment? What can we expect regarding weather, wildlife viewing, etc? Should I postpone this trip for a year or more? I want this to be a positive experience for my children.

How Well El Nino in 2015 Effect Western Wisconsin and how well this effect us getting hit, what well the weather be like. well many be likely not able to survive this?

My mom and I are planning a trip to the Yucatan for February 2016 and she's worried it's going to rain a lot or they'd get hurricanes. What will the weather be like in that region during El Niño?

The first thing to say about this blog is how well it is written. No Mysto-crypto-tech jargon, so common in many disciplines. A huge thank you to authors. You actually want first and foremost to communicate - not hide and nuance things, and impress readers with your knowledge . This is deeply appreciated. WG

What is the projected effect on the west coast of Mexico, Mexico City and the Yucatan in February-March 2016?

What normally happens to Caribbean tradewinds when el nino is strong?

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