El Nino post write up for August

 

I’ve been trying to post these little updates on the developing El Nino every few weeks. This will cover the developing conditions in the Pacific.

El Nino and La Nina Explained

courtesy of NOAA’s National Ocean Service

The waters of the eastern tropical Pacific Ocean continue to warm as we approach the end of meteorological summer. This El Nino is expected to continue strengthening over the Fall, then reach its peak sometime in winter or early Spring 2024.

It’s only the middle of August now it’s pushing global temperatures to the 1.5 ºC climate threshold,

Sea Surface Temperature (SST) Anomaly …

 Global SST…

 

courtesy of Coral Reef Watch

 

Pacific SST…

 

 

courtesy of Coral Reef Watch

 

Atlantic SST…

 

 

Phases of El Nino…

There are East Based, Central Based, and West Based

Snow lovers hate East Based El Nino

Central Based (Modoki)

A Modoki is just when the greatest warm water anomalies are centered near the Dateline, this allows for a deep trough to setup south of the Aleutians.  While Modoki’s can be blocky in the Atlantic, that’s not always the case. Modoki’s are a mixed bag.   The trough in the Pacific shifts back and forth between the Gulf of Alaska and the Aleutian Islands, resulting in a up and down pattern, where high latitude blocking shifts west and east between Iceland and Canada. So, what type of winter events we see can vary greatly.  Modoki winters can experience wild swings in temperature, resulting in rain, mix, and snow events. It’s all about the timing of the cold air outbreaks and the current storm track.

West Based sets up closer to ideal, the 500 mb pattern along with the polar and subtropical jet, making for a better chance for a snowy season.

 

Currently we’re in a very strong East Based El Nino. But looking at the subsurface water temperature progression and other signs that this is shifting west.

  

Strength of El Nino…

Judging the impacts of an El Nino isn’t just about the phase of ENSO we are in. But we have to include the strength of the event too. You can have weak, moderate or strong El Nino phases. Typically, stronger El Nino’s bring more impactful weather to parts of the United States, especially for California and the southwest, compared to weaker El Nino phases.

 The strength is determined by how much above average the water temperatures are in the Niño 3.4 region.

.Weak El Nino (with a 0.5 to 0.9 SST anomaly), Moderate El Nino (1.0 to 1.4), Strong El Nino (1.5 to 1.9) and Very Strong (Super) (≥ 2.0) events.

The latest weekly SST departures are:

Niño 4 0.9ºC

Niño 3.4 1.2ºC

Niño 3 1.8ºC

Niño 1+2 3.3ºC

Currently the developing El Nino is considered moderate to strong. The northern hemisphere ocean/atmosphere system has coupled, with what is going on in the equatorial Pacific.  During El Nino we typically see an active northern polar jet, with an active and amplified southern sub-tropical jet. That has certainly been the case for the last several months.

We should note that, for historical context, the most accepted method of categorizing the intensity of El Nino’s and their opposite, La Nina’s, utilize NOAA's three-month running mean SST anomaly, known as the Oceanic Nino Index (ONI), instead of looking at one week or even one month's worth of data.

Subsurface water temperature.

 

Latest SOI index

The SOI is a tool we use to determine how the ocean and atmosphere dynamics are evolving.

 

The current SOI is indicating the atmosphere is responding to a weak to moderate El Nino signal.  This could be part of the reason for some of the disconnect we’re seeing in the ocean/atmosphere system. This is just one of the reasons this El Nino, isn’t acting as a typical El Nino would.  

 

 The most recent IRI plume indicates El Nino will persist through the Northern Hemisphere winter 2023-2024.

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Some of the factors in play…

Hunga Tonga-Hunga Ha'apai volcano (Yep, I’m still talking about it.) underwater eruption in the South Pacific Ocean occurred Jan. 13 to Jan. 15, 2022. The eruption blasted an enormous plume of water vapor and enormous quantities of ash and volcanic gases into Earth's stratosphere. All of this is still affecting the Stratosphere and in turn the troposphere

there are a number of other factors that have contributed to how this year has been, including going from La Nina to El Nino, the current Solar cycle, the Tonga-Hunga Ha'apai eruption leading to a reduction in atmospheric particulates allowing more sunlight to reach the surface. All of these factors, added to a generally warming planet. Mean the Planet is going to warm even more, and become much more volatile.  

All of this is changing the pattern, in ways that the outcome isn’t clear.  We have never had a super warm Atlantic Basin during an El Nino. This is having a big impact on the hurricane season. Typically, during El Nino, conditions over the tropical Atlantic are more hostile resulting in fewer tropical cyclones. But this year, the warm water in the Atlantic, is making for a likely above average season.   Like wise the Northeast has been extremely humid this summer, again that is the result of how all of these factors are interacting with each other. So, we’re more or less in uncharted territory when it comes to how this current El Nino is going to act like.  

A few thoughts on what this might mean for winter 2023-2024…

A winter outlook involves the speed and amount of Eurasia snow growth, sea ice extent, movement of the QBO, The very warm Global Oceans. And many other things. Much of these things we can’t look at for at least a couple of months; So, we have a long way to go, before an outlook can be released. So, while it’s way too early to talk about specifics, we can at least apply a broad brush to the subject.

We have to remember, no two El Nino’s are alike, when looking only at the five previous strong El Nino’s, there are some general commonalities to note headed into winter 2023-2024.

El Nino years following triple-dip La Nina.

. 1957, 1976, 2002, 2023

Some analogues I’m considering…

1957-1958, 1965-1966, 1972-1973, 1982-1983, 1986-1987, 2002-2003, 2015-2016.

 

An El Nino Modoki is just when the greatest warm water anomalies are centered near the Dateline, forcing a deep trough in a really nice spot south of the Aleutians. they're also quite blocky in the Atlantic

These analogues include East Based, Central Based and Western Based. I have to include all of them, because this El Nino is still strengthening and evolving.  But we are starting to see shifting forcing west.  So right now, we have a chance for a Motoki or even a west based El Nino event.  I’m leaning toward the idea of this being a hybrid Modoki and West Based event. But there is a chance this could end up as a basin wide event. This too would make for a fairly decent winter as well.

 The farther west this warming water can get the greater the likelihood for low pressure setup up in the western Aleutians, this would increase the odds for favorable high latitude blocking. How and where the blocking set up will be a major deal this winter. The QBO will also have a lot to say on how much blocking we see, a negative QBO and ascending would increase the odds for more blocking.

In general, Northeast and Middle Atlantic winters tend to be overall warmer and wetter during an El Nino. During strong El Nino’s we tend to see less overall snow. But as I’ve already said, no two El Nino’s are exactly the same.

During the super El Nino’s of 1982-83 and 1997-98 there were big 2nd half of winter snow events.

The winters of 1957-58 and 1965-66 were cold.

But El Nino is only one factor when it comes to how a winter will end up being. As I’ve already pointed out Blocking will be another major influence. Blocking involves the North Atlantic Oscillation (NAO)  

 

Here is a look at snowfall from 1950 to 2017 in nine Northeast Cities, broken down by El Nino, La Nina and neutral seasons, as well as those stronger El Nino seasons with a dominant positive or negative NAO.

We can see there is the sharp contrast in strong El Nino’s depending on whether they're dominated by a positive or negative NAO.

 The strong El Nino seasons dominated by a negative NAO produced the snowiest seasons.  More North Atlantic Ocean blocking of the jet stream in a negative NAO pattern would allow the polar jet stream to plunge southward in the eastern U.S., bringing ample cold air. A powerful subtropical jet stream, typical in strong El Nino seasons, would interact with the cold air, perhaps coupling with the nosediving polar jet, making East Coast snowstorms more possible.

 The 2009-10 season featured a moderate El Nino dominated by strongly negative NAO. The result was the snowiest season on record in Philadelphia and Washington D.C.  and the second-snowiest season in Pittsburgh. Conversely, with the exception of Washington D.C., all other Northeast cities tended to see the least snow during strong El Nino /positive NAO seasons. These seasons often featured the polar jet stream pushing cold air eastward across Canada rather than plunging deep into the East. With the dominant subtropical jet stream unable to meet cold air or interact with the polar jet, few Northeast snowstorms would result.

The bottom line, I’m still thinking this will be very strong El Nino, how this coming winter turns out will depend on the degree of blocking. The overall pattern is such that nobody is sure what kind of winter we’re going to see, but right now I’m thinking moderate to severe end of the spectrum.