Tuesday, September 22, 2009

Ocean Science 101: Effects of El Nino on the Winter 2009-2010 Surf Season

Hey gang…I have a couple of people ask me about the how the current El Nino conditions are going to affect our surf this winter…so I thought I would put a little post together.

I think that it is important to start with the understanding that just having “El Nino” conditions does not guarantee that Southern California will get good surf.

Weather is so ridiculously dynamic, and there are just too many factors that feed into storm generation (not to mention swell production), for us to really get a “for sure” long-range outlook that goes further out than a few days. Forecasting for a winter season that is still a couple of months away is more about comparing the developing atmospheric and oceanic conditions against previous seasons…and then applying statistical probability to the season ahead. In short it is basically educated guesswork, backed by historical data…we can analyze until we are blue in the face but we won’t know how things will turn out until after the fact.

Ok enough buzz-kill talk…the good news is that why El Nino doesn’t “guarantee” good surf, it does significantly increase the likelihood of storms forming lower in latitude and closer to the West Coast, both of which are “good things” for sending swell into Southern California…and, in general, the stronger the El Nino the higher the probability of these types of storms forming.

As of the last update from NOAA’s Climate Prediction Center we are currently experiencing a moderate El Nino so far this fall…and that these conditions are likely to continue into the winter…possibly strengthening if some of the pieces can hold in place over the next month. You can actually check out the latest update here…

http://www.cpc.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

“Moderate” in this case actually means that the current conditions are weighing in on the strong side of the bell curve…basically this year’s El Nino will be stronger than most of the recorded El Ninos that we have experienced over the past 30+ years…with only a few of the really intense ones (1982-83, 1987-88, 1997-98) coming in stronger.

Here is a shot of the current Sea-Surface-Temps (SST) and the SST anomaly, which is the difference in sea temps against the historical “seasonal mean” temps. In the anomaly map the more yellowish-red that shows over by Central America the stronger the El Nino.



Why this matters for Southern California…

With El Nino there are two important air/ocean changes that occur that have a significant effect on the winter surf for Southern California. (Bear with me…it takes a little bit of explaining to get there.)

1. The shift of the jet streams (both the Polar and Pacific Jet stream).

2. The amount of warm water (and corresponding warm air-mass) that is available to fuel storm intensification.

During El Nino the jet streams that push eastward over the pacific shift slightly…we see the colder polar-jet move further northward, over Alaska and Canada, rather than flowing over the Gulf of Alaska. We also see the Pacific jet stream, which is a warmer and usually less stable in its position, strengthen and flatten out across the mid-latitudes. The combination of these two shifts effectively opens up the storm track and allows swell-producing storms to form in more southerly positions, which puts them more firmly in SoCal’s W-WNW swell window.



In point #2…The warmer water piling up on the eastern half of the Pacific…which is usually pushed along the equator off to the west…is basically a giant power-battery storing sunlight as “latent-heat energy”. All of this energy is usually over past Hawaii, towards the Philippines, helping fuel WPAC Typhoons/Cyclones and bleeding extra-tropical goodness into those hyper-intense storms that make the Kamchatka Peninsula such a nice place to visit.

By repositioning that energy in the EPAC, storms that would have generally been starting to lose strength as they hit the cooler waters off of California and the Pacific NW, now have much more energy (in the form of warm/wet air-mass) to continue intensification. As most of you know…stronger storms, closer to your position, mean bigger swell.


A shot of the 97-98 El Nino and how crazy hot the water in the EPAC got


What this means for our surf…

With the moderate El Nino conditions expected to either continue (or strengthen) as we head into this winter season, we can expect to see stronger and better positioned storms forming in the Southern California swell window. With more intensity and more time in the swell window the incoming swells should be both bigger and last longer as they push into our region. Overall we should have a much better “surf” winter than we have had over the last couple of years.

One other thing that we do have to keep in mind is that with the lower latitude/more intense storm track combining with a lot of warm/unstable air-mass filtering up from the tropics this winter is liable to be a lot “wetter” than the previous couple of winters. So while we get increased swell action, we also get the potential for crappy conditions as the storms push over top our region.

I don’t know about you guys…I am willing to sacrifice a few days to junky weather in order to get some more consistent surf.

Anyways…If you guys are into diving in a much more detailed analysis of this winter’s El Nino and all of the factors that go into measuring estimating it…I would go and check Mark Sponsor’s winter/El Nino outlook over at http://www.stormsurf.com/ ...here is the link (make sure to visit a few of Mark’s advertisers in appreciation of his extremely thorough work.)

http://www.stormsurf.com/page2/enso/current.shtml

Bonus Section: What is an El Nino?

I realize that I wrote most of this post with the assumption that you guys understand the general concept of El Nino conditions…but just in case that part of science class was a little fuzzy…here is a fairly simple explanation of what occurs during an “El Nino” year.

The term El Nino refers to a particular portion of a 3- to 10-year circulation pattern of ocean/atmospheric conditions that cycle primarily through the Pacific Ocean (but are believed to affect weather conditions throughout the world). The scientific community generally refers to this pattern as El Nino-Southern Oscillation (or ENSO) and it has two distinct phases on either ends of its intensity…El Nino (the warm part) and La Nina (the cold part).

When El Nino occurs it is because the usual pattern of trade winds in the Pacific Ocean along the equator are disrupted, and the winds that normally push warm water to the west away from Central America stop, and sometimes even blow the opposite direction.

Without the trade winds, warm water stays in position near Central America and begins to spread along the coasts of North and South America. Since warm water is basically the Sun’s energy stored as heat, it means that a significant amount of energy has been allowed to shift to a completely new position in the ocean. This shift has an incredible effect on the Pacific Storm Track…and has been linked to changes in weather all over the Earth.

The strength of an El Nino is generally measured by the increase in the water temperatures in the East Pacific as compared to the seasonal average. If water temps raise above the average it is considered El Nino (and if they drop below the average it is considered a La Nina).

Generally…for Southern California…El Nino has a positive effect on swell producing storms for our region…while La Nina has a negative effect. This isn’t 100% on either side…(it is possible to have a bad winter even with an El Nino)...but the trends do tend to follow those patterns.

Like I said…this is a very simple explanation of what occurs in the ENSO circulation…if you want more details, the Wikipedia entry is a pretty good place to start…

http://en.wikipedia.org/wiki/El_Ni%C3%B1o-Southern_Oscillation

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Anyways…I hope this answers a few questions on El Nino and how it will hopefully lead to a better winter surf season. Personally I am ready to have a quality winter…no more one-hit wonders.

Cheers...here's to a good winter!

Adam

Adam Wright
Forecaster
http://www.socalsurf.com/

8 comments:

Danimal said...

So that 6'6" pintail I just ordered might see some action?

Whiffleboy said...

Thanks, Adam!

Anonymous said...

2 words = FUCK YES!

Anonymous said...

wow, thanks man.

Anonymous said...

Thanks AW!
You can really see that warm water trying to penetrate and impreganate the eastern pacific on the Sea Surface Temperature (STD?) shot.
Plus it looks like Mike Hawk.
I am taking that as a good omen a long with another killer post.
U d Man, we demand!
Coconutz!

deckmanx said...

What might this mean for other parts of the EPAC? Namely: Baja, Central America, and South America?

SC fool said...

Cheers!

bajajoaquin said...

My understanding of the "Southern Oscillation" part of ENSO is that the El Nino event is only half of the global event. For the increase in surface temperature in the East, with its corresponding drop in atmospheric pressure (mightily simplifying here), there is a corresponding decrease in SST and increase in atmospheric pressure in the West.

Because of this, El Nino events on our side tend to be mirrored by droughts and wildfires in West Oz, and by failure of the Monsoon in India.

So the "oscillation" is a switch in weather patterns on each side of the Pacific.

It's been some time since I studied it, so I may be wrong. Can you comment?