El Nino is officially here.

 

The National Oceanic and Atmospheric Administration has issued an El Nino advisory, announcing the official arrival of El Nino. There are several factors in place might make this El Nino different than other El Nino’s in the past.

The last El Nino event to impact the country was during 2018-19, this event was very weak. Since then, we had a triple dip La Nina, meaning a La Nina that covered three consecutive years.  

Nino region 3.4 is where we usually monitor the El Nino-Southern Oscillation (ENSO) for El Nino or La Nina. As I’ve said many times, an El Nino is when sea surface temperature anomalies reach 0.5 °C or warmer than average values for a three-month period.  When we look at the monthly Nino index in each of the four Nino regions, we see that they are all above 0.5 C.  Nino 3.4’s anomaly is at 0.98°C above average, meaning we’re on the cusp of a Moderate El Nino, Nino region 3 is at +1.1°C, Region 1+2 is much warmer at +2.6°C. 

The strength is determined by how much above average the water temperatures are in the Nino 3.4 region. The stronger the El Nino the greater it’s impacts. I posted in the blog, about what is a Super El Nino which you can find here.

Water temperatures 0.5ºC above average = Weak El Nino

Water temperatures 1.0ºC above average = Moderate El Nino

Water temperatures 1.5ºC above average = Strong El Nino

Water Temperatures of 2.0+ above average = Super El Nino

When we look at the subsurface water temperatures in the equatorial Pacific, we can see there is a lot of warmer than average water below the surface, coupled with those very warm SST off of Peru and Ecuador. While this is a good indicator of a strong El Nino down the road; they aren’t a 100% guarantee that a strong El Nino will develop.  When we look at the historic record, the SST in the equatorial Pacific is currently the 4^th warmest for May.  The top two May values were 1997 and 2015, both of these become super El Nino’s.  The El Nino of 1979 into 1980 lasted into the Summer of 1980, 1980 saw the third warmest water in the Central Pacific for the month of May. But that didn’t result in a strong El Nino, instead that El Nino was a weak Modoki El Nino.  A Modoki El Nino is when the SST in the central Pacific is warmer than in the eastern Pacific

This El Nino has started early based on the historic average. The early bird El Nino has formed roughly two months early.  The vast majority of El Nino’s are at their strongest during December to April, with the greatest impact during December through February, But the early start might make a difference in this. If the El Nino strengthens quickly it could affect both temperatures and rainfall this summer.

The Southern Oscillation Index (SOI)...

The SOI is a good indictor of how the overall atmosphere is responding to the ENSO. The more negative the SOI the stronger the El Nino. Sustained negative values below about –8 indicate an El Nino.

Over the last several weeks, both the equatorial SOI and traditional SOI were significantly negative.

The Madden-Julian Oscillation (MJO)...

The MJO is currently sitting in phase 3 and is very weak. The MJO is looking to transition to phase 4 and looks to stay there at least through the Middle of June. After that the models show it collapsing into the Circle of Death (COD) for the 2nd half of June and remains there for the foreseeable future. Phase 3 is typically a warm signal for the Northeast. But Phase 4 is a cool signal.  Once the MJO reaches the COD, it will loose most of its influence on the overall pattern, allowing other forces to be in control of the overall show. Seeing the MJO in the COD during the summer months is fairly typical due to the generally weaker trade winds. The MJO is looking to support overall temperatures staying below average to near average for much of June before allowing for more warming during July.

This should allow for the pattern over the CONUS to adjust to become zonal. Over the last several weeks, the pattern over the northern CONUS has been stuck in a roadblock. So, we’ve been having these upper-level lows (ULL) setting up and hanging around the Northeast.  The idea of these ULL spinning over the Great Lakes and Northeast is typical for El Nino. But lately this idea has been on steroids.  With the pattern more Zonal, we would have systems moving freely from west to east.  This would allow us to return to overall average/slightly below average temperatures across the Northeast, which would be a big change from the overall well below average temperatures we’ve been experiencing for the last few weeks.  So, with the El Nino, while we will see troughs over the Northeast, there shouldn’t be as many of them as we’ve seen the last several weeks. 

This general idea is supported by the CPC 8–14-day temperature and precipitation outlooks.

 

The Atlantic is also very warm...

Typically, El Nino creates more in the way of hostile atmospheric conditions of higher amounts of windshear. The higher windshear helps to disrupt tropical formation in the Atlantic Basin. Typically, during El Nino, the Atlantic sees cooler SST; the lower water temperatures are also unsupportive for tropical cyclone development.   This year Atlantic SST are much different. The warm SST are over a large part of the North Atlantic, including the Main Development Region. The combination of El Nino, the large amount of warm water in the north Pacific, and the very warm SST in the Atlantic Basin, is really nothing that we’ve seen before. So, we’re kind of in uncharted territory, when it comes to this year’s El Nino.   

The warmth in the Atlantic is going to help counteract the impact of El Nino on the 2023 hurricane season. This is one of the reasons My hurricane outlook is calling for average to above average tropical cyclone numbers in the Atlantic for this season.  

 

El Nino impacts for this Summer and upcoming Winter...

During El Nino years overall temperatures are warm across much of the CONUS, part of this has to do with the fact that typically during El Nino overnight temperatures are warmer when compared to afternoon temperature anomalies. This hanging on to the heat, helps to raise overall summertime temperature anomalies when they are averaged together.

In the summer months, the eastern U.S. typically sees cooler-than-average temperatures, with more in the way of dry condition, this is especially true for the Northeast. I showed this in my Summer Outlook which you can find here. Remember, the stronger the El Nino the more pronounced the impacts.

During the winter months, the northern tier of the CONUS including the Northeast it tends to be warmer than average, while the southern tier is colder than average. The Middle Atlantic region tends to see overall average to slightly below average overall temperatures. Precipitation is typically average to above average. But the temperatures make P-type is highly variable. Generally, snowfall is below average across the interior Northeast, this is largely due to the polar jet stream's diversion north, keeping the region warmer than average. The Middle Atlantic tends to due better on Snowfall during El Nino, typically seeing average to above average snowfall.

But the idea of this being a strong El Nino will have an effect on all of this. For the Northeast and northern Middle Atlantic Region, the phase of the MJO is as or more important than El Nino when it comes to snowfall in this region.

Here is a chart for cities in the Northeast and how the strength of the El Nino and the phase of the North Atlantic Oscillation (NAO) generally has on snowfall totals.

 

Showing snowfall from 1950 to 2017, broken down by El Nino, La Nina and neutral (neither El Nino nor La Nina) seasons, as well as those stronger El Nino seasons with a predominant positive (+) or negative (-) NAO.

In seven of the nine Northeast cities examined, strong El Nino seasons with a prevalent negative NAO produced the snowiest seasons compared to average.  The reason for this is when the NAO is negative it promotes a general pattern supporting Blocking near Greenland. Along with a better chance for the polar jet stream to push south, allowing for colder air at times. During strong El Nino’s the subtropical jet is typically very active and has a better chance of interacting with the northern Jet, when the polar jet is farther south.  This increases the odds for bigger Northeast snowstorms.

On the contrary, with the exception of Washington D.C., all other Northeast cities tended on average to see the least snow during strong El Nino and generally positive NAO.   The reason being the polar jet stream stayed eastward up across Canada keeping the cold air bottled up in Canada. These kept the subtropical jet stream from interacting with the polar jet, with a general lack of cold, meaning there were few chances for Northeast snowstorms.

That covers the latest on the developing El Nino, and how it could impact this Summer and a little glimpse of what it could mean for the Winter of 2023-2024.