Why the hurricane season was so active?

 

A little overview of the 2023 Atlantic hurricane season.

The 2023 Atlantic hurricane season, officially ended on Nov. 30. In spite of it being a strong El Nino; The season was very active. In fact, the 2023 Atlantic hurricane season ranks 4th for most-named storms in a year. Looking at the numbers, there were 20 named storms (including an unnamed subtropical storm that formed on January 16), seven of which were hurricanes, three of them became major hurricanes, and the season had an overall Accumulated Cyclone Energy (ACE) of 146. In total there were 3 landfalling tropical cyclones on the U.S. main land. The numbers show 2023 saw the most named storms in the Atlantic basin of any El Nino influenced year in the official record.

For comparison, based on data from 1991 to 2020, an average season typically sees 14 named storms, seven hurricanes, and three major hurricanes.

2023’s 20 named storms, ended up a tie with 1933 which also saw 20 named storms. The three years that surpassed 2023 numbers were, 2021 which had 21, 2005 which saw 28, and 2020 which saw 30.

I released part three of the hurricane outlook back in May, my final numbers were 14-20 named storms, 8-12 hurricanes, 3-5 major hurricanes. The CONUS would see 2-4 landfalls with one of them possibility being major. The ACE would be 100-150.

So overall my outlook verified very well.

Looking at the storm tracks map

We can see the Atlantic itself was exceptionally active, while the Caribbean and Gulf of Mexico saw hardly any activity.  

 Image credit WGNO in New Orleans

 Landfalling Systems:

Three Atlantic storms made landfall on the U.S., Major Hurricane Idalia and two U.S. landfalling Tropical Storms Harold and Ophelia.

The first U.S. landfall of the 2023 Atlantic hurricane season came on August 22nd as Tropical Storm Harold moved ashore Padre Island in South Texas with 50 mph winds, causing minor damage and localized flooding across the southwestern U.S.

The second landfalling system Idalia was the only hurricane to hit the US this year. She started as an area of disturbed weather over the eastern Pacific. She then moved across Central America into the northwestern Caribbean, where she slowly organized, becoming a tropical depression on the 26^th of August; she became a tropical storm on the 27^th.   By early Monday morning on the 28th, Idalia began her northward turn and after crossing the western tip of Cuba Monday night, Idalia would rapidly intensify from a tropical storm into a major hurricane on Tuesday the 29^th over the Gulf of Mexico. She obtained major category 4 hurricane status with sustained winds of 130 mph. Then right before landfall, she underwent an eyewall replacement cycle which allowed her to weaken slightly to a 125-mph category 3 hurricane. She made landfall in Florida’s Big Bend, near Keaton Beach, Fla bringing storm surge flooding up to 7 to 12 feet, on Aug. 30, 2023 at 7:45 a.m.

The third was Tropical Storm Ophelia which made a landfall at Emerald Isle, North Carolina on September 23. With maximum sustained winds of 70 mph, Ophelia’s widespread heavy rainfall, significant river and storm surge flooding across eastern North Carolina. She also brought heavy rainfall to such cities as New York City, Washington, D.C. and Philadelphia.

While Hurricane Lee didn’t make a U.S. landfall it was a close call, Lee formed in early September, soon after he rapidly intensified into a Category 5 hurricane. After transitioning from a hurricane to a post-tropical cyclone, Lee made his landfall in western Nova Scotia, Canada, on September 16. Lee was a large storm with Hurricane-force winds were extending up to 140 miles from the center of Lee and tropical-storm-force winds were extending up to 390 miles from the center. Due to his size, Lee’s swells created high surf and rip currents along the entire U.S. Atlantic coast. Lee’s strong winds, with gusts to over hurricane strength, caused extensive power outages in Maine and parts of Canada.

Why the hurricane season was so active?

 When the tropical eastern-central Pacific Ocean is unusually warm, El Niño can form. During El Niño events, the warm upper-ocean temperatures change the vertical and east-west atmospheric circulation in the tropics. That initiates a teleconnection by affecting the east-west winds in the upper atmosphere throughout the tropics, ultimately resulting in stronger vertical wind shear in the Atlantic basin. That wind shear can tamp down hurricanes.

Typically, during El Nino, the warm upper-ocean temperatures in the equatorial Pacific change the vertical and east-west atmospheric circulation in the tropics, which customarily means sea surface temperatures in the Atlantic Basin tend to be cooler than average. Also, characteristically El Nino features increased atmospheric stability and vertical wind shear in the Atlantic; historically all of these created conditions that hamper storm development in the Atlantic. But as I showed in the tropical activity storm tracks, 2023 has acted anything but a typical year with increased storm activity in the main north Atlantic.

In general, hurricanes are more likely to form and intensify when a tropical low-pressure system encounters an environment with warm upper-ocean temperatures, plenty of moisture in the atmosphere, instability and weak vertical wind shear.

The East Pacific also was very active this year, all this activity created conditions that favored sinking air over the Gulf of Mexico (GOM) and Caribbean. This was one reason the Caribbean and Gulf we’re extremely quiet during the season.

In the Atlantic, there were three major factors that worked together that heightened the environment needed to increase the number of storms. Atlantic sea-surface temperatures, weak wind shear, and the location and strength of the Azores/Bermuda high.  All three of these things are so intertwined that they really can’t be described by themselves.  

1 Warm Atlantic sea-surface temperatures:

Atlantic, sea temperatures this summer were unusually high with record high temperatures which counterbalanced the strong El Nino. This made it easier for storms to form and develop.  The Atlantic went through a series of marine heatwaves. 

The pattern over the US and Atlantic Basin, played a big role.

We had a large heat dome over Central U.S along with a persistent blocking pattern over the Labrador Sea, Greenland and Iceland. This was the reason, for the cooler and wet spring into summer.  This high latitude blocking means that there is higher than average pressure in that region. This also typically leads to lower-than-average pressure near Bermuda and the Azores, which was the case this year.

2 Azores/Bermuda high:

The Azores/Bermuda sub-tropical high is a pressure system that sits over the Atlantic in the summer. It acts as a barrier to hurricanes, and can shift in size and location. Once storms clear the high, they head north.

Over the hurricane season this subtropical high was weaker and farther east than average. Both of these things had major impacts on tropical storm development.

A weaker Bermuda/Azores high, means the easterly trade winds are weaker. Because the trades are weaker, there is much less upwelling of cooler water from below the surface. As a result, the water keeps warming. This occurred in a big way in the Main Development Region" of the tropical Atlantic this season. The tropical Atlantic warmed at a faster rate than ever before. With the trade winds much weaker than average there was no upwelling so the water stayed hot much longer than is typical.

3 Wind Shear:

Wind shear over the open Atlantic and Main Development Region in 2023 was much weaker than is typical during an El Nino.  On the other hand, the shear was a little stronger over the Gulf of Mexico, Caribbean and along the East Coast.

wind shear refers to the variation in wind speed and direction with height in the atmosphere. For the 2023 hurricane season wind shear was generally strong near the East Coast and generally weaker out over the open Atlantic.

For a tropical system to develop and strengthen, wind shear needs to be low. The higher the wind shear, the more difficult it is for a tropical system to organize and strengthen. Generally speaking, you want wind shear to be less than 20 kt for a system to develop. Higher than that the wind shear disrupts the structure of tropical storms. For rapid intensification to occur you want the wind shear to be 10 kt or less.

The weaker easterly winds kept Saharan Dust to a minimum during the season. With there being much less dust than average over the north Atlantic, more of the Sun’s energy reached the surface of the Ocean. All of these factors led to the Atlantic Basin seeing record breaking ocean water temperatures. And allowed the Atlantic to more or less overrule the influence from the strong El Nino in the Pacific.

While Atmospheric and Ocean conditions over the Atlantic Basin allowed for higher amounts of tropical cyclones in spite of El Nino. There was one El Nino influence that impacted the Atlantic Basin. That would be steering currents over the Atlantic Basin.

The placement and weakness of the subtropical high setup and environment allowed storms to turn north into the open Atlantic well before reaching the U.S. or even the Caribbean. So, storms like Category 5 Lee and Category 4 Hurricane Franklin veered away from the U.S. mainland.  If the Bermuda high had been strong and farther this summer, storms would have made it into western Atlantic, with the likely outcome of more U.S. landfalling tropical cyclones.

The arrows on the 500mb show the general direction of the steering flow.

The large heat dome ridge over the Plains and the persistent trough of low pressure in the Northeast was also a player in the storm track pattern that kept storms out of the GOM and away from the East Coast. If there had been more in the way of stronger high pressure over the Northeast into the Midwest, there would have been a better chance for them to be trapped under the high with no escape to recurve away, increasing the odds of landfalling systems.   

Well, that’s a basic rundown on why the 2023 hurricane season went the way it did.

 

 

 

The 2023 - 2024 Winter Outlook Part Three.

 

The days and nights are getting colder, most of us have had our killing frost, and some of us have had our first snow of the early season.  So, with the 2023-2024 winter right around the corner, the thought “what is this winter going to be like?” is growing more and more common across the region.  So that means it’s time for my Winter Outlook for the Northeast and Middle Atlantic.  Many of y’all look forward to what could be instore, where I combine a bit of science with pinch of conjecture and a spoonful of past patterns that were similar, and try to come up with the general weather patterns for the coming winter season, trying to show the overall temperature possibilities along with potential snowfall in store for the region.

The last few winters have been lackluster to say the least, many snow lovers would likely say they have been complete disasters. The Northeast has many businesses and communities that rely on winter snowfall for economic wellbeing.  With the idea of a strong El Nino that will impact this upcoming winter, many winter lovers are feeling very antsy.  

Parts one and two laid the groundwork for part three. Part three will go into the El Nino a little bit more, along with some of the different ENSO indexes. I will cover on how the snow extent and ice coverage have been progressing. I will also talk about the Quasi-Biennial Oscillation, or QBO. Lastly, I will try to go into the temperature, precipitation, snowfall amounts, and the storm tracks we could see

If you don't want to read the technical stuff, you can skip to the bottom.

Link to part one

Link to part two

 Sea Surface Temperature anomalies:

 

Above is the latest surface analysis of the global oceans. We can see the marked warm anomalies of the El Nino event in the equatorial Pacific, reaching over 4 degrees Celsius.  The well above average water anomalies also stands out across the Atlantic Basin.

The image below, show SST anomalies in the ENSO region of the equatorial Pacific over the last two years. The blue box shows the La Nina last year and how ocean temperatures quickly warmed to become our current El Nino event. The red box shows the forecasted peak values this El Nino could achieve over the Winter 2023/2024.

 

El Nino Southern Oscillation (ENSO):

ENSO is the most important coupled ocean-atmosphere phenomenon to cause global climate variability. During El Nino, we typically have a very active subtropical jet stream and an amplified polar jet stream. With the extended and amplified subtropical jet with many areas of low pressure moving along it. The southern U.S. typically sees, several storms with lots of precipitation and cooler weather. This general pattern can lead to frequent strong Gulf and East Coast Storms.

You can see exactly that in the jet stream anomaly forecast below for January 2024. It shows the typical strong subtropical jet stream over the southern United States (red).

 

NOAA bases the phase of ENSO by and large on the Oceanic Nino index (ONI).

The ONI is based on SST departures from average in the Nino 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO.

Below is an image showing the Nino Regions across the equatorial Pacific

 

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.

CPC considers El Nino or La Nina conditions to occur when the monthly Nino3.4 OISST

departures meet or exceed +/- 0.5ºC along with consistent atmospheric features. These

anomalies must also be forecasted to persist for 3 consecutive months.

The IRI multi-model image below show the consensus that El Nino will peak around +2 degrees above normal. That is considered a strong event. But the forecasts also agree that the El Nino will start to dissolve somewhere towards Summer 2024.

 

Based on the ONI, we’re in a strong El Nino right now, with SST anomalies in Nino 3.4 being 1.8°C above average. We will likely see this peak around 2.0°C, before it levels off and then drops back toward a moderate El Nino for the 2^nd half of winter.  I don’t think this El Nino will end up as strong as the Super El Nino of 2015 to 2016.

On the Facebook weather pages and in past blog post, I’ve talked about ENSO indexes, such as the SST anomalies like the ONI and Southern Oscillation Index. The ENSO is the biggest climate driver on the planet, for this reason over the years several ways have come up to measure it.  Besides the SST indexes and SOI, there is the wind index, outgoing longwave radiation index, and the multivariate ENSO index. Each of these Indexes have strong points and limitations.

I want to focus on the multivariate ENSO index (MEI).

The MEI, is a method used to characterize the intensity of an ENSO event. Given that ENSO arises from a complex interaction of a variety of climate systems, MEI is regarded as the most comprehensive index for monitoring ENSO since it combines analysis of oceanic and atmospheric variables.

 While NOAA is showing we’re in a strong El Nino, looking at the MEI images below, we can see it’s showing more in the way of a weak to moderate El Nino. Since sometimes we see more cold and snowy conditions during weak to moderate El Nino’s than we typically do during strong El Nino’s.

 

The way the atmosphere is responding to El Nino, is supporting what the MEI is showing.

 In part one and two, I talked about the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and the Pacific Decadal Oscillation (PDO).  As I’ve said, The ENSO isn’t the only deciding teleconnection, as other factors have to also be factored in.

Here in the Northeast, the actual correlation from the impact of El Nino is very weak, when compared to many other places. So, it’s very problematic to say El Nino will produce this or that kind of impact here in the Northeast.  So, while the El Nino could likely override the other contributing factors in other parts of the U.S. Here in the Northeast El Nino, might not rule the roost.  For the Northeast our snowfall potential is often driven by the NAO, AO, and other teleconnections including the Madden-Julian Oscillation (MJO). In the previous parts I went into NAO, AO and the PDO. The factors I laid out are still valid. But I do what to talk a bit on the QBO.

 Quasi-Biennial Oscillation:

The QBO, is another teleconnection that is a prime driver of global climate. The QBO is winds in the stratosphere 15km to 50km over our heads. As with all teleconnections the QBO has two phases.  An easterly (negative) phase, when the winds in the stratosphere blow in an easterly direction, and a westerly (positive) phase when the stratospheric winds blow in a westerly direction.  The QBO is very predictable with the phase changes occurring about every 14 months.

The QBO influences the strength of the polar vortex. When the QBO is in a positive phase, the odds for a strong polar vortex increases. During the negative phase the chances increase for the polar vortex to be weaker, increasing the likelihood for some cold air intrusions into the U.S. When the QBO is easterly, there is a better chance for the AO and NAO to be generally negative.

Currently the QBO is negative, this will increase the odds for high latitude blocking along with a better chance for polar vortex disruptions, increasing the odds for cold air incursions during this winter.    

 Eurasian Snow Extent:

In part two, I said, Eurasian Snow cover was below average over Siberia. Since then, more snow as fallen over Siberia.  

 

I’ve placed a box on the Rutgers Snow Extent map, showing the area in Eurasia where we’re concerned with in Siberia. There is a color scale that shows how much above or below average snowfall extent is. The coral tones show where snow cover is below average; whereas, the blue tones show where snow cover is above average. Looking at the map, we can see most of that area is colored in a light shade of blue, which indicates snow extent in Eurasia is slightly above average for this time of year.

 

The Chart from 1967 to 2023 is also showing snow cover is just slightly above average.  Snow cover is indicating a slightly better chance for a colder and more in the way of snowy winter in the Northeast and Middle Atlantic.  As we saw last winter, snowfall was well below average across the region. When we look at the chart, we can see the snow extent was even lower last winter than now.  

 Sea Ice:

On the map from the National Snow and Ice Data Center, I’ve placed a red box over the Barents-Kara Sea.  The map shows the sea ice extent that is monitored for possible influences on our winter weather. We can see that well over half of the area is ice free. The Charts show Ice extent is well below average

Some meteorologist (myself included) thinks the less sea ice over the Barents-Kara Sea, the more likely the chance for the polar vortex to be weaker, increasing the likelihood for cold air intrusions into the U.S.  

 OK let’s get into the Maps and Idea’s I have for the 2023-2024 winter.

 Temperature Outlook for Winter 2023-24:

Even though El Nino’s impact here in the Northeast is a bit tricky, it does produce general impacts. In general, we expect temperatures to run milder than average in moderate to strong El Nino winters.

 

Based on the data I've shown, this isn't likely to be a downright frigid winter. But we will see cold air outbreaks that extend southward out of Canada from time to time.

Eastern Canada is going to end up with overall below average temperatures -1°F to -3°F. So sometimes we will see cold air outbreaks into the Northeast depending on the timing we could end up with a few major nor’easters.

Around the Great Lakes and far Northern New York State and Northern New England temperatures look to be overall above average

From Pittsburgh up through the Finger Lakes, Central New York State, Northern Hudson Valley, Northern Vermont and Northern New Hampshire into Central Maine, temperatures look to be slightly above average.

For Central Pennsylvania, Central Hudson Valley, Central New England, and Southern Maine will end up with overall average temperatures, +1°F to -1°F for the winter. Southern Maryland, Delaware, and southern New Jersey will end up below average -2°F to -3°F. With the Southeast being well below average temperatures -3°F to -4°F

The upper Great Lakes look to be +2°F to +3°F above average.

 Storm Track Analysis for Winter 2023-24:

The southern subtropical jet is going to stay very active, with a lot of Pacific Moisture moving along it.

There will be frigid air north of the polar Jet

We will have disturbances moving along a fairly active polar Jet. The northern Jet is going to be bouncing around a bit.

The highly amplified and extended subtropical Jet, will support moisture across the southern U.S. The low pressure that will move across the southern U.S. Bringing snowfall across the Southeast. Some of these storms will move up the East Coast, increasing the odds for snowfall across the Middle Atlantic and perhaps Southern New England.

The polar jet is going to be to be just north of the Northeast. Given the pattern that is looking to setup, there is increased chances for sudden stratospheric warming events, that will lead to disruptions in the polar vortex, increasing the odds for cold air intrusions into the Northeast and Middle Atlantic. Given proper timing, there will be snowfall opportunities, especially from Mid-Winter into March.

The image below shows the general pressure pattern during past El Nino events. It shows low pressure over the North Pacific, strong high pressure over Canada and lesser high pressure over the North Atlantic near Greenland. It also shows the low-pressure storm track over the southern U.S. 

  

The pattern will support several snowfall opportunities for the Northeast and Middle Atlantic, we’ve already seeing several coastal storms this fall. So, Miller A and Miller B northeasters could be quite possible during this upcoming winter. While we will most likely see some lake cutters, I don’t think that will be the predominate storm track like we saw last winter.

Given those extremely warm SST in the Atlantic, if we have some cold that drops down from the Arctic, the warm SST could help support a strengthening coastal low. the greater the temperature gradient the stronger the potential of the nor'easter. Depending on the track this setup would also be capable of producing influence of a cold conveyor belt, which would help set up zones of heavier snow. Warm SST's during December can work against big snowstorms, but during the 2nd half of the winter, those warm SST can be a snow lovers’ best friend.

Precipitation Outlook for Winter 2023-24:

Rain, sleet, freezing rain, and snow

Southern and eastern Pennsylvania, Southeast New York State and the Central Hudson Valley, across central New England into southern Maine look to see of generally 10% above average precipitation While Southeast New England, New Jersey, Southeast Pennsylvania, Maryland and Delaware end up generally 20% above average.

The Great Lakes, northwest Pennsylvania and western New York State look to see slightly below average precipitation at -10%

The rest of New York State and northern Vermont, northern New Hampshire and northern Maine ending up with generally average overall precipitation.

 

 

Snowfall Outlook for Winter 2023-24:

These snowfall amounts are overall general ideas for the Northeast and Middle Atlantic for this winter. I base this on the general teleconnection pattern and what I anticipate to be the general storm tracks.

As for how much snow we should expect this winter, well, specific numbers are hard to nail down but with a weak to moderate El Nino in the picture, along with the pattern I describe above, I see support for an above average snowfall season for Southern New England, Southeast New York State (including New York City and Long Island into the Middle Atlantic, With the area around the Appalachian’s ending up as the jackpot, with good odds for well above average snowfall.

Slightly above average snowfall for most of Northern New England into Northwest Massachusetts, Hudson Valley and the Catskills, along with the Twin Tiers of New York State and Pennsylvania, back through most of Western Pennsylvania

Northern and Central New York State and the Adirondacks into Northern Vermont, looks to see near average snowfall. Northwest Pennsylvania away from Lake Erie could also see average snowfall.  

Slightly below average lake effect snows off of Lake Erie. With around average lake snow off of Lake Ontario.

 

A general look month by month:

December:

Temperatures…

Past Thanksgiving into the first week of December is looking to generally be below average, then we should see some warming, resulting in slightly above to above average temperatures up through the time around mid-month, then we look to see general temperatures become slightly below to below average for the end of December.

Overall temperatures should generally end up fairly mild with above average for the month of December.

Snowfall…

For the month I expect generally slightly below average snowfall.

 

January:

January is going to continue to see the up and down temperature roller coaster. The month could start slightly below average. Then there would be the chance for temperatures to warm back up near average to above average, before falling back to average to below average during the 2^nd half of January.

The subtropical jet, will stay active during the month. We could see many of the southern storms head out to sea; but we could see a few of these storms come up the coast. While Western Pennsylvania up through Western New York State, see generally below average snowfall, for Eastern Pennsylvania the rest of New York State into New England see generally average snowfall typically for the month of January.  

 February:

The last half of the winter, is likely going to be colder and snowier than the first half.  February as a whole should see Western parts of the region with slightly below average overall temperatures. The temperatures across Northern into Central New York State and the Northern half of New England, end up with overall temperatures near average, Southern New England, back through Southeast New York State, Eastern Pennsylvania, and the Middle Atlantic should see below average temperatures.

Based on this being an El Nino winter and climatology, February should end up a big snow month. The Southern and Northern jets should stay active. During past El Nino’s, nor’easters are common off the Coast. So, I will be very surprised if we don’t see at least a couple big coastal storms come up the coast, bringing snow across the Eastern half of Pennsylvania, Maryland, Delaware, into New York State along with New England. As we saw during the Super El Nino of 2015-2016, Coastal storms can bring significant snowfall into the Middle Atlantic and Northeast, even during El Nino years.

As far as snowfall, Western New York State, and Western Pennsylvania should generally see slightly above average snowfall With Central into Eastern Pennsylvania and New York State seeing above average snowfall, with possibly well above average snowfall for the Middle Atlantic into Southern and perhaps Eastern New England.  

 March:

Temperatures should be overall above average in the Northeast and Middle Atlantic Region, especially during the 2^nd half of the Month.  With generally below average snowfall across Western Pennsylvania and Western New York State, with average to slightly below average snowfall over Eastern Pennsylvania, Eastern New York State, into the Middle Atlantic and New England.

 Closing thoughts:

.Remember seasonal outlooks are deterministic in nature, so with the overall idea of randomness in mind, different outcomes are always possible. Afterall the law of averages, insist that everything must level out, so these different outputs are expected.

This winter is going to see wild swings between warm and cold temperatures, So snowfall is going to depend on the overall pressure pattern and the timing of the individual storms. So, get ready for a wild ride.  Also with the temperature going back and forth, it will be more difficult to develop a deep snowpack. So while snowfall may indeed end up above average, we might not see long lasting snow banks.  

Well, that’s it

I hope you found this multipart outlook interesting and educational. As always, I can’t answer questions about the outlook from other outlets. But I will always answer all y’all’s questions in regards to my outlooks and forecast.

 

2023 2024 winter outlook part two

 

Part two will cover what this year’s tropical activity can tell us, snow cover in Siberia, and talk about some of the teleconnections like the Pacific Decadal Oscillation.

To read part one follow this link

I've been working on this and trying to figure out the best way to present it in the most concise straightforward and easy to understand format. Which is far from an easy task. 

I’ve tried to take a balanced approach to what I’m seeing this year. Remember a winter outlook is an overview of what the entire winter season should feature. This outlook isn’t going to cover storm details on snow amounts or track, it will feature a broad overlook of the general pattern we will likely see at times during this winter.

 

Sea Surface Temperature (SST) anomalies…

 

Teleconnections:

Our atmosphere is very fluid. These fluid properties are constantly changing over time and location. What’s going on over one part of the Planet has a downstream impact somewhere else.  A deepening ridge, means a trough must dig.  The weather patterns in other parts of the world are called teleconnections.

During the winter, changes in the phases of certain teleconnections can produce conditions favorable for a cold and snowy pattern in the Northeast and Mid-Atlantic Region. Besides the El Nino Southern Oscillation (ENSO) the other teleconnections we generally look at are the Artic Oscillation (AO), Eastern Pacific Oscillation (EPO), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Pacific-North American Pattern (PNA).

 

The El Nino Southern Oscillation (ENSO)…

One of the winter major forecast factors to look at in the late fall/winter is the state of the ENSO. The ENSO is a fluctuating weather pattern around the equator in the Pacific. The cool negative phase is called La Nina where we see cooler than average sea-surface temperatures equatorial Pacific, the warm positive phase is called El Nino where we see warmer than average sea-surface temperatures in the equatorial Pacific.  Part, one talks about how this years ENSO and the developing El Nino are shaping up.    

 

El Nino

A lot of people including many meteorologists are placing a lot of importance on this El Nino and how it may be a Super El Nino. But while a moderate to strong El Nino is likely; we could fall short of super El Nino status.  

This isn’t going to be a normal El Nino

Strong El Nino’s  1957-58,1965-66,1973-74,82-83,1991-92,1997-98,2009-10,-2015-16

During El Nino we typically see a less-active, west-to-east storm track across the northern US. The subtropical Jet stream is also typically quite active.

Why was the Atlantic tropical season so active?

We had recorded warm water.

But the shear didn’t tear them apart as much

Could it be due to the placement of that shear?

The warm water in the Indian Ocean (a positive IOD) is one major reason. Another reason is the record warmth in the Atlantic Basin.

So, we got a lot of convection (rising air) around Africa and a lot of subsidence (sinking air) around the South Pacific Islands, that helps displace a lot of the lifting. So, we had rising air near and around Africa and lifting air over the Eastern into Central Atlantic. But we had sinking air in the Caribbean and Gulf of Mexico, so we didn't see much development in a large part of the Caribbean and GOM. The warm Atlantic overruled El Nino conditions.  

Typically, South America is very wet during an El Nino. But this year South America is experiencing major drought

So, it looks like the warm water around the Equatorial regions, shifted El Nino’s influence east, resulting in a very active 2023 hurricane season.

  

 We also have to look at the northern Pacific…

 

The Pacific Decadal Oscillation (PDO)

 The PDO deals with sea surface temperature anomalies over the Northern Pacific (north of 20° north latitude), as with all teleconnections it has a positive and negative phase. These phases typically last for decades. The PDO represents the oceans response to the atmosphere.  In this way it is a prime driver for low pressure systems in the north Pacific, for example the Aleutian low-pressure system in the Gulf of Alaska. Depending on how strong this low is, it will have a different impact on wind flow, and the pressure gradient. If the Aleutian Low is very strong, we tend to see a stronger southernly flow along the immediate West Coast.

The positive phase is characterized by cool SSTs north of Hawaii and warmer than average SSTs in the Gulf of Alaska and along the West Coast of North America. The negative phase we see the opposite, warmer than average SSTs north of Hawaii and cooler than average SSTs in the Gulf of Alaska and along the West Coast of North America.

During the positive phase the Mid-Atlantic and Northeast is more likely to experience overall below average temperatures for December, January and February. During the negative phase the opposite is true, with the Mid-Atlantic and Northeast likely to experience overall above average temperatures for December, January and February.

The PDO has been negative for the last several winters. But the last couple of months has seeing it quickly moving towards neutral after being negative for the last four straight years. The last time this setup occurred was during the Fall of 2002. The winter that followed was a very decent winter snow wise here in the Northeast.

So, while this is theoretically a negative PDO. it really isn’t a textbook negative PDO. During a typical negative PDO the water is much colder in the Gulf of Alaska and west coast of Alaska, the cold water would also typically extend down into the Pacific Northwest. So, while the water is cooler it isn’t as cold as you would expect to see during a negative PDO.

The PDO and the Pacific North American Pattern (PNA)

There is a direct correlation link between the PDO and the PNA. During the winter the correlation is greater than 0.80.

The PNA is closely related to the strength of the Aleutian Low and the strength of the PDO

The PNA for our purposes here, is the PNA is the main driver of the trough ridge pattern over North America

During a negative PNA there typically is more overall upper level troughing over the western U.S leading to cooler and wetter conditions, while the eastern U.S. is more likely to see overall ridging leading to drier and warmer conditions. During a positive PNA the eastern U.S. sees more in the way of troughing while the western U.S. sees more in the way of ridging.   

 

Last winter, we had a negative PDO and a negative PNA during January and February that combination resulted in very warm temperatures across the Northeast and Mid-Atlantic Region.

 

The PDO and the ENSO

During El Nino, the Aleutian Low is generally stronger than average during the winter months; this favors a positive PDO pattern. The opposite is true during La Nina; the Aleutian Low is generally weaker than average during the winter months, which favors a negative PDO pattern.

A negative PDO favors a weaker El Nino or a stronger La Nina. A positive PDO favors a stronger and longer lasting El Nino or a weaker La Nina

This is going to be at least a moderate El Nino winter, with a strong likelihood of the El Nino being strong. So, since this isn’t a La Nina year. There is a strong signal that this winter will feature a positive PDO. What we’re seeing in the SSTs in the northern Pacific supports this idea, of a developing positive PDO.

 

When the PDO and the PNA are in opposite phases, they are working against each other (Destructive interference)

 

As I said above, the other major teleconnections we look at during the winter are the AO, EPO, and the NAO. Unlike the ENSO PDO and to a lesser extent the PNA; these three have a tendency to fluctuate between phases every couple of weeks or so.   

 

Artic Oscillation (AO)

The AO deals with the strength of the Polar Vortex (PV) and determines whether or not there will be a supply of Arctic air available to fuel winter weather. I will explain more about the PV when I discuss the current snow cover. But, a positive AO indicates that the PV will be strong and Arctic air will stay locked up near the pole while a negative AO indicates the potential for a weaker PV leading to the chance for Arctic air to escape southward.

Eastern Pacific Oscillation (EPO)

During the winter, the state of the EPO controls whether there is, a cross-polar path for very cold Arctic and Siberian air to flow across the pole and down into central and eastern North America.  During a negative EPO, a ridge builds over Alaska. The more amplified this ridge is, the greater the chance for cross-polar flow. Conversely, a positive EPO indicates a large, persistent low in the Gulf of Alaska and results in warmer weather for the lower 48.

 

 

North Atlantic Oscillation (NAO)

The NAO, in its negative state, indicates high-latitude blocking over Greenland. This lingering area of high pressure causes the flow to stagnate. The storm track is often underneath it and can result in persistent storminess for the Eastern US. On the contrary, a positive NAO has no such block and the storm track moves quickly across the CONUS and out into the Atlantic.

Can the eastern US still get winter weather with a positive NAO? Yes, but they’re often quick-hitters and rarely significant events.

The ideal configuration for a period of winter weather in the eastern US is a negative NAO, negative AO, negative EPO, positive PDO and a positive PNA. Can other combinations still produce winter weather? Sure, but this combination is almost a guarantee.

 

Snow cover:

Since it is still October, I remain focused on the snow cover advance across Siberia and what impact it may have on the stratospheric polar vortex (PV).  I am sure I will be discussing this pathway more in the coming months.  More extensive snow cover across Eurasia in October, and this mostly confined to Siberia, the more likely the PV will be weaker than normal during the winter months that favors widespread colder temperatures across the Northern Hemisphere (NH) but in particular in East Asia and the US east of the Rockies.

The more widespread snow cover is across Siberia during October, the more we’re likely to see a weaker than average stratospheric Polar Vortex (PV) during December through February. The PV is a large area of low pressure that sits over the Pole during the winter. When snow cover in Siberia is above average, it favors the negative phase of the Arctic Oscillation (AO).  When the Arctic Oscillation is in its positive phase, the jet stream, which brings us  a large part of our weather in middle latitudes, tends to shift to the north. So, when the AO is positive, the polar vortex is generally strong and in a tight circle, with cold air bottled up over the Arctic. When the AO is negative, the PV tends to be weak and much wavier meaning it is prone to collapse, this increases the likelihood of cold outbreaks here in the U.S. east of the Rockies.  

So far this year, snow cover over Siberia has been well below average, but over the last couple of weeks this departure has been reversing. Snow cover over northern Canada isn’t really seeing any big improvement in snow cover. But in general, the larger the snow cover extent in Asia and Canada in the Fall, the better the chances for stronger polar air outbreaks during the winter.

 

We will have to keep an eye on this; as there is still time for the snow cover over Canada and Eurasia to increase.  

 

Here is what I’m thinking based on how things look to be trending….

Right now, the closest the atmospheric setup and pattern resemble is the winters of 2002-2003 and 2009-2010. Those winters saw generally colder temperatures and some snowy periods

I do think we’re going to have a predominate positive PDO and positive PNA. This would allow for the potential for cooler overall temperatures for the winter of 2023-2024 here in the Northeast and Middle Atlantic. But storm tracks and temperatures will depend on the phases of the AO, NAO and EPO.

Real winter will be slow to start, with overall temperatures in December running average to slightly above average. January will see generally average overall temperatures. Then February into March will see overall temperatures below average.  This isn’t going to be the coldest winter on record; but it also won’t be the warmest winter on record. Those predicting a torch for the entire winter are likely on the wrong side of what looks to transpire.

There will be blocking setting up near Greenland at times. Depending on how the polar vortex acts during those times will determine the amount of cold that will be available.  

We’ve already had some early season nor’easters. I think the winter is going to feature a few nor’easters that come up the Coast from the Gulf of Mexico (Miller A nor’easters) and some storms that move into the Ohio Valley that then transfer to the Middle Atlantic Coast (Miller B nor’easters). The tracks will depend on the alinement of the teleconnections, if we have a negative AO along with a negative west-based NAO, it would favor a snowstorm bringing the chance meaningful snow for parts of the region. But if the negative NAO is east-based, the storms would likely form too far east to bring much in the way of snow to parts of the region.  How much cold these storms have will depend on the phase of the EPO, if the timing works out, then a negative EPO would bring the opportunity for at least a moderate polar airmass over the region.  

The amount of snow this winter will be very dependent on your location. Those in western parts of our region, will likely see overall snow amounts that are average to below average, with central and northern parts of the region ending up generally with overall average seasonal snow amounts. Those in the Middle Atlantic into southern New England, will have the greatest chance of seeing overall above average seasonal snow totals.  The winter pattern that looks to be setting up will likely see at least one to two big nor’easter events from mid-January, February into early March.  These storms would have the potential to bring major snowfall across the Middle Atlantic, I-95 Corridor into Southern New England. We’ve seen these kinds of winters before, where one or two big storms made up the bulk of the winter snow.   

 

Well that’s it for now.

Part three can be found here