There is no
doubt that the season is running below the historical average at this point in
the hurricane season as of today, the 2022 season has had 6 named storms, 2 of
which become hurricanes, with none of them officially becoming a major
hurricane. When we look at the 1991-2020 climatological average, by now we
should have seen around 8 named storms, 3 hurricanes, and 1 major hurricane. While
numerically the Atlantic is below average. Another index is even more telling.
Here is the current Accumulated Cyclone Energy chart from Colorado State University
(September 14th, 2022). The ACE index is the most accurate way to measure overall seasonal tropical activity; the reason is that it not only takes the strength of the tropical cyclones, but also the energy used by a tropical cyclone during its lifetime. The seasonal total is the sum the ace used by each individual tropical cyclone during the season. The Chart shows that. Current ACE is running around 29.6, the average for September 14th is 67.1; That’s a difference of 77.544% of the average value for this date in the season. So, we’re running about 56% below what it should be this time of year.
When we look at other years that had active early starts. We see many changes. I saw these when Joe Bastardi posted on this subject not too long ago.
This year
has acted very odd. Most of the vorticity has been north of the Main
Development region. One statistic that shows just how odd, is where the
tropical cyclones formed in 2022, 86% of the tropical activity in the Atlantic
Basin has occurred in the subtropical and extratropical Atlantic. That is an extraordinary
statistic, showing just how strange this season has been.
Why is
the current La Nina different from the La Nina of 2020 and 2021?
A La Nina occurs
when the sea surface temperature in the equatorial eastern Pacific Ocean is at
least 0.5°C cooler than the long-term average.
NOAA
Operational Definitions for El Nino and La Nina
El Nino:
characterized by a positive ONI greater than or equal to +0.5ºC.
La Nina:
characterized by a negative ONI less than or equal to -0.5ºC.
By
historical standards, to be classified as a full-fledged El Nino or La Nina
episode,
these
thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month
seasons.
That is something that we have seen during the last two winters: 2020-2021 & 2021-2022. As you can see in the graph below, we have remained in a La Nina pattern much of the last two years except a few months in the mid of 2021.
It is a
common misconception that all La Nina’s are the same.
While La Nina
only occurs in the Pacific equatorial tropics, its impacts are felt in many
parts of the world. This happens because the location of the enormous mass of
cold water, may cause the location of the jet stream, or storm track, to shift.
As a consequence, some regions can become warmer or colder, or wetter or drier,
than the historic average. However, not all La Nina events have the same
strength or location, and consequently their impacts can vary significantly.
During La
Nina seasons the Atlantic tends to be more active, due to higher average SST,
Lower average wind shear and generally better odds of rising air. This year’s
La Nina has allowed for higher SST in the MDR. But overall, the Atlantic has
seen higher wind shear than is typical for La Nina. There has also been a lot
of Saharan Dust over the tropical Atlantic.
The reasons
for the extra shear the Saharan Dust acting the way it has, will be explained
below.
Why is
this happening?
There are
several natural reasons, But the major one is the Sea Surface Temperatures (SSTs)
in the northern Atlantic. SSTs are warm enough in the tropical Atlantic to
support tropical development. The problem is SST’s north of the Main
Development Region (MDR) are also very warm. If you remember your science from
School, what goes up must come down. So, rising motion in one part of the
atmosphere … leads to a sinking motion in another part of the atmosphere.
Looking at
the SST over the last couple of years, we can see there are several differences
between Atlantic SST this year compared to the last two.
When we look
at the current global 5km SST anomalies from NOAA Coral Reef Watch
We see all
that warm water in the high latitudes in the northern Pacific and northern
Atlantic. Both of these areas are part
of the problem this year in both the Pacific and Atlantic. The result of this
is the overall pattern has been warped. This distortion has affected many
things, not the least of which is having above average sinking air in the
Tropical Atlantic and changed steering patterns. Does this have to do with a warming climate?
Most likely, at least in part. But as I’ve explained many times, this warming
is being caused primarily by too much water vapor, and to a much lesser extent Co2.
But regardless of the reason, the fact remains the planet is warming.
The warm SST
in the northern Atlantic is the reason for the increased wind shear over the
Atlantic; this shear is the reason the dust from the Sahara is sticking around,
and not dissipating as fast as it would on average. These warm SST are also the
leading cause for the heat wave that has plagued Europe since early July.
Looking at the NOAA 500mb Geopotential Height chart you can see the overall northern Hemisphere pattern starting in January. The ridging clearly shows all that heat directed into Europe. The warm northern Atlantic and the heat ridge, with the northeast flow is causing upwelling which is also leading to those cooler SST in the Eastern Atlantic.
That strong
Bermuda-Azores high that has been dominating the Atlantic, is one of the strongest
we’ve seen in a while, The BA is the primary reason the SAL is so prevalent. The
easterly jet stream picks up this dust from the Sahara Desert and pushes it
westward across the Atlantic Ocean. The
dust heats up the atmosphere, making it more stable and less conductive for the
development of convection (thunderstorms). There is a lot of dry air over the
tropical Atlantic, Tropical systems need high levels of atmospheric moisture in
order to maintain convection and strength. With such a large amount of dry air
in much of the tropical Atlantic, there is little moisture, inorder for systems
to become more organized and have the chance at formation. The Bermuda high has
been a little further south so far this season, which is why the storms were
tracking further south in the Atlantic into the far southern Caribbean for the
first half of the season. End of August
into September, we saw the BA push more north and east. This allowed for Danielle
and Earl to recurve out into the open Atlantic. Those warm SST in the northern
Atlantic is the reason they became hurricanes so far north. Tropical Storm Fiona
which formed last night (September 14th; is going to track
farther south and west because that double barreled high to her north is
building west. So, she can’t cut to the north.
Another
reason for this year’s tropical Atlantic setup has been the Madden-Julian
Oscillation (MJO) it has primarily been in phases that favored tropical cyclone
activity in north east Pacific, to the determent for tropical activity
everywhere else.
But the
truth is, tropical cyclones have an almost impossible chance of developing in a
dry dusty area with sinking air, which is the reason for the season’s behavior
so far.
Is the
season over?
No, not by a
long shot. The odds of the 2022 hurricane season being hyperactive is likely over.
But there is still a chance for the season to recover and perhaps end up
average to above average. I think we will see at least some tropical activity
in late November, maybe even beyond that. The SST in the Western Atlantic, Caribbean,
and Eastern Gulf of Mexico are very warm. If we can get the right upper air
conditions, a tropical cyclone could cause havoc along the East Coast or
Northern Gulf Coast. An example would be Hurricane Michael which rapidly
intensified before landfall. Moving into the Panhandle of Florida a Category 5.
How the
weather pattern is evolving?
The pattern that is setting up …the pattern the Euro operational and the ensemble is hinting at is interesting, for the early fall, thru at least mid-October … we look to see predominate troughing set up between the central Aleutians and the western Gulf of Alaska. Leading to a transient trough on the immediate west coast. A ridge over the Rockies into the Plains, with a positively tilted trough around the Eastern U.S. With the trough axis over the East Coast and the Atlantic Ridge, were going to see the same pattern we’ve been seeing the last week to 10 days, where the trough and ridge pop…these stationary fronts try to come in. So, we will see a lot of humidity, very warm night time lows and near to slightly above average day time highs.
What we’re
seeing is a transition in EL Nino/Southern Oscillation (ENSO). The ENSO is the overriding
pattern that leads to El Nino and La Nina.
We’re still
in that La Nina state. But we’re starting to see some changes in the equatorial
subsurface SST. Where the subsurface is starting to moderate…ENSO 4 has
basically started to wane, ENSO 3.4 and 3 hasn’t really changed too much, and
hasn’t pushed any closer to the surface. And we’re seeing an expansion in
Subsurface water temps in the western Pacific, which hasn’t pushed up to the
surface. So, this means that the Pacific is trying to become more neutral. So,
we could see ENSO neutral declared by January into February.
A more
important signal is the SOI
The SOI is
an excellent indicator of the Atmospheric response involving the ENSO.
We want to
focus on the 30 and 90 anomalies. Compared to the readings during mid-summer to
now, the readings have by slowly and steadily declining. This means that La
Nina won’t crash and disappear. It’s going to slowly go away. So, when you have the La Nina slowly
transitioning, combined with a lot of other volatile interactions, like the
increase in water vapor from volcanic eruptions, below average sea ice in the
arctic, you combine those factors and you end up with this environment here….
looking at the subtropical jet stream. Why is that important?
In a strong
to moderate La Nina, the Polar Jet Stream is king, it dominates everything, it
can march across the Pacific and drive a Pacific air mass right across the
CONUS, making snow lovers cry everywhere.
It can develop a trough over the northern Plains into the Great Lakes,
setting the Northeast up for the dreaded Southeast Ridge, with storms cutting
to the Great Lakes. During these conditions it is very difficult to get high
latitude blocking to set up, because the jet stream is moving too fast.
In a strong
El Nino it’s the subtropical jet that is king. It’s too powerful, driving short
wave after short wave into the Southwest, it leads to large southern severe
outbreaks, because you have those shortwaves marching across. And it prevents
the polar Jet Stream from digging, so the cold air gets blocked off and stays
in Canada. So High Latitude blocking doesn’t get the chance to really develop.
Since the subtropical jet is overriding everything ocean storms develop too far
off the coast, and the northeast ends up getting rain and a cold blustery day.
But during
weakening stages of El Nino and La Nina, you end up with an environment where
the Polar Jet is strong and the subtropical jet is strong. But neither one
overwhelms the other. So, you get more interactions between the two streams,
which leads to more phasing, if phasing works out just right, it can enhance
high latitude blocking, which leads to big coastal snowstorms and lots of snow.
