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.
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 4th
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 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.
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