Letās cut right to the chase. According to the September El NiƱo-Southern Oscillation (aka āENSOā) Outlook, El NiƱo is expected to stick around (with greater than a 95% chance) at least through January-March 2024. There is now around a 71% chance that this event peaks as a strong El NiƱo this winter (Oceanic NiƱo Index ā„ 1.5 ĖCelsius). Remember, though, a strong El NiƱo does not necessarily mean strong El NiƱo impacts locally. Instead, it means a stronger chance that El NiƱo impacts will occur.
Letās dive deeper into whatās going on across the Pacific in a patented ENSO Blog expert Q&A. And boy, oh boy, are you not going to believe who we were lucky enough to snag. Without further ado, introducing our two āexpertsā: the Pacific Ocean and the tropical atmosphere.
ENSO Blog: Letās start in the water. Pacific Ocean, big fan. Can you go over what āyouā have been up to in the last month?
The Pacific Ocean: Hey, right back at you! Itās flattering that you have an entire blog dedicated to things going on in me. But letās focus on whatās going on at my waist, what you call āthe equator.ā The main El NiƱo monitoring metric, the NiƱo-3.4 indexāthe average sea surface temperature in the central and eastern equatorial Pacific Oceanāwas 1.3ĖCelsius (2.3ĖFahrenheit) above the long-term average in August, up from 1ĖC in July, according to the most reliable dataset, ERSSTv5 (long-term here is 1991-2020.) And the June-August NiƱo-3.4 index was 1.1ĖC above the long-term average, making it the third consecutive three-month period in El NiƱo territory. And from what Iāve read on your blog, that means you are two more seasons away from an official āEl NiƱo episodeā in the historical record (the red in this table.)
Plus, judging from your weekly sea surface temperature datasets of my belly, the NiƱo-3.4 temperature anomalies are even higher during the first part of September, up to 1.6ĖC.
EB: Thatās pretty hot!
The Pacific Ocean: Iām pretty hot all over. In fact, my cousins the Atlantic, Indian, Arctic, and Southern Ocean are all pretty hot at the moment. Like record-breaking hot from April till now. So hot that the warmer-than-average ocean temperatures associated with El NiƱo happening in my central/eastern mid-section do not nearly stick out in the global picture as much as events in the past. Itās bonkers, if you ask me. The whole ocean was over 1ĖC above the 20th-century average in August, the first time thatās happened in the 174-yr record. All us oceans have a fever!
EB: As we all know; El NiƱo doesnāt work if the atmosphere isnāt also playing. So, my next question is for the tropical atmosphere. Whatās going on with you?
The tropical atmosphere: Thanks for having me. First-time guest, long-time reader. Believe me, El NiƱoās got me all topsy-turvy. Normally when my Walker Circulation is acting like a well-oiled machine, there is rising, moist air over the warm western Pacific Ocean, sinking air over the eastern Pacific, and winds connecting those two branches: trade winds blowing east to west at the surface and west-to-east winds high up in the atmosphere. El NiƱo messes all of that up. And thatās what has been going on.
In August, the trade winds were weaker over the east-central equatorial Pacific. More thunderstorm activity than normal occurred farther east, extending from the international date line to the eastern Pacific Ocean, which is totally not where these storms typically reside. And then two important atmospheric metrics that you humans use, the Equatorial Southern Oscillation Index and the Southern Oscillation Indexāwhich monitor how the surface air pressure changes between the western and eastern Pacific part of meāboth were strongly negative in August, indicating an El NiƱo-like weakening of pressure in the eastern Pacific and higher than normal pressure in the west.
EB: How similar have recent precipitation patterns been to El NiƱo?
The tropical atmosphere: Take a look at these images comparing the global precipitation anomalies from June-August 2023 to how I typically behave during El NiƱo. Oh, Iāve been very El NiƱo-like! Not only has precipitation been above-average across the equatorial Pacific Ocean, but it has also been below-average over northern South America, Central America, and parts of Indonesia and India.
Now, itās not a perfect match. I know, I knowā¦youāll call me unreliable. Flighty. Chaotic, even. I prefer to say that I, the tropical atmosphere, never repeat myself. I give each El NiƱo its own special touch. Still, this yearās rainfall patterns are pretty close to previous yearsā El NiƱos. In fact, based on a measure of pattern similarity between these two images, out of the 11 El NiƱo summers on record, June-August 2023 was the third-best match to what you all call the classic El NiƱo pattern (footnote #1). Only the summers of 1997 and 2015 were more like El NiƱo. Remember those events? Pretty big El NiƱos. So yeah, you could say that El NiƱo is having an impact on me.
The Pacific Ocean: Ā How about we ask you a question now? ENSO Blog writer Tom, what can we, the Pacific Ocean and tropical atmosphere, expect from El NiƱo for the rest of the year?
Tom: Well, thatās a first. But great question! The global climate models we rely on are pretty certain that the currently observed warmer-than-average sea surface temperatures will last and even strengthen through winter 2023ā24. After which, this El NiƱo event is expected to weaken, which is normal for these types of events.
The continued model confidence is one reason why forecasters have odds of over 70% that the current event will peak as a āstrongā El NiƱo (NiƱo-3.4 index values greater than 1.5ĖC) for the November-January average. There is even a 30% chance that NiƱo-3.4 values exceed 2.0ĖC by this winter, which would put ocean temperatures in a tier with some of the strongest El NiƱos since 1950.
But to our readers, a few reminders from the ENSO Blog archive.
- You cannot blame EVERYTHING on El NiƱo.
- No two El NiƱos are alike, and the same goes for their impacts. And,
- Just because a strong event is forecasted does not necessarily mean strong impacts. Instead, El NiƱo can increase the chances for certain types of extremes.
That about does it for this monthās post on the ENSO Outlook. A special thanks to the Pacific Ocean and tropical atmosphere for taking some time out of their chaotic days and answering a few of my questions.
The Pacific Ocean: Of course! [waves goodbye]
The tropical atmosphere: An honor to be invited. [Blows a kiss]
Footnote
- If you look at the spatial (pattern) correlation coefficient between the two images, the coefficient is ~0.6, meaning that about 36% of the global spatial variability is explained by El NiƱo. This is a pretty large number as far as these things go!
This post first appeared on the climate.gov ENSO Blog.