weather – Swell Lines

El Niño w/Mark Sponsler

*Mark Sponsler is the creator of StormSurf.com, “a website dedicated to delivering the highest quality marine weather data to those who ride waves.” Sponsler’s weekly forecast videos focus on El Nino indicators year round, regardless of media hype.

El Nino can have profound effects on global weather and ocean conditions. Under normal conditions, trade winds over the equatorial Pacific blow from east to west (Peru towards Asia). This causes warm water to sequester near Asia, and cool water to upwell off Peru. This in turn results in high pressure over the cool water off Peru (producing stable atmospheric conditions) while low pressure and tropical precipitation locks down off Asia.

But about once every 7 years, the trade winds over the equator relax if not reverse direction, with the effect being a flow that travels reverse of the normal direction, or from west to east (Asia towards Peru). When the trades relax or weaken, this situation is know as westerly anomalies. That is, compared to normal for the time of year, the winds have a westerly component to them And when trades fully reverse (they start blowing from the west to the east), this is known as a Westerly Wind Burst (WWB).

A Westerly WInd Burst across the equatorial Pacific Ocean. — A Westerly Wind Burst across the equatorial Pacific Ocean.

WWBs can last for 10-20 days and can blow as hard as 20+ kts. This situation typically occur between New Guinea and the International dateline. When a WWB occurs, it sets the oceans surface in motion moving to the east. The result is warm water off Asia starts migrating east across the tropical Pacific towards Peru. WWBs also typically spawn tropical cyclones, sometimes straddling both sides of the equator simultaneously. Typically the westerly anomaly/WWB cycle starts in Spring or early Summer, with a single WWB, followed by 2-4 more through early Fall, with the warmest waters reaching Ecuador around Christmas.

The warm water doesn’t flow from west to east on the surface. It falls to depth, down about 200 meters, forming a pocket or bubble of anomalously warm water (+7 degs C above normal). That pocket is called a Kelvin Wave, and it travels west to east under the equator for 2.5 months before being forced to the surface first as it encounters the Galapagos Islands, then eventually impacts Ecuador. For each WWB that occurs during the EL Nino cycle, a corresponding Kelvin Wave develops. The more WWBs, the more Kelvin Waves, and the greater the warming in the east.

As a Kelvin Wave erupts in the East Pacific, it warms surface water there, and typically pretty dramatically. This in turn has effects on fisheries and wildlife, especially in the Galapagos, Peru, Central American corridor. Where normally cold upwelled nutrient rich waters are present, now a warmer and far less bountiful food chain is present for fish. Fish stocks leave the area. Local economies that survive off fishing turn non-productive.

Eventually these warm waters, as they erupt near the Galapagos start migrating west by prevailing trades over the East Pacific, moving towards the dateline. Note – the trades don’t completely dissipate in the east. As this cycle progresses, a defined warm water ‘tongue’ develops extending from the Galapagos east and within 5 degrees north and south of the equator reaching west to the the dateline. Depending how warm the surface pool gets and how much area it covers compared to normal determines whether the situation will qualify to be labeled as El Nino. The area of concern is from 5N to 5S and from 120W to 170W, the NINO3.4 area. If temps in this region hold at +0.5 deg C above normal for 3 months, it considered a minimal El Nino. At the top end temps of +1.5 result in a classification of a strong El Nino. As of the Sept monthly reading, this years event was at +1.67 degs C. In comparison, the two strongest El Ninos at their peak in Dec/Jan were at +2.32 (’97/98) and +2.21 (’82/83). Theses were considered Super El Ninos. This years event is already the 6th strongest El Nino ever (as of Sept), and building. And it is tracking mid-way on it’s development path between the ’82/83 and the ’97/98 events, making it possible it too could reach Super El Nino status.

As the surface warm pool builds, it starts interacting with the atmosphere above it, enabling greater evaporation and increasing humidity levels, reducing surface air pressure and increasing the odds for rain in locations of the planet typically bone dry. Likewise as water cools over Asia, surface air pressure builds and drought sets in. Precipitation follows the warmer water across the Pacific, resulting in a complete reversal of the Pacific Basin weather patten.

From a surf perspective, the weather changes associated with El Nino are most pronounced in Fall and Winter months in the Northern Hemisphere. The warm pool feeds more energy into the jetstream, which in turns causes the jet to track further south forming a strong semi-permanent low pressure system just east of the dateline and south of the Aleutians easing into the Gulf of Alaska. The upper level energy feeds development of larger, stronger and more consistent storms tracking across the Norther Pacific, which in turn generates larger, stronger and more consistent surf aimed at breaks in which the jetstream is flowing towards, like Hawaii, California, the Pacific Northwest, Mexico. But because the jetstream is further south, it also offers the specter of much rain and stormy local conditions, making surf conditions less than ideal. During pronounced episodes during strong El Nino years, the jetstream can drive storm energy straight from Siberia clear across the Pacific and directly into the US, often tracking right into normally drier regions of Central and Southern California. This can bring significant rain and snowfall to regions that are typically desert like, having severe economic and ecologic affects. In the Atlantic, the El Nino enhanced jetstream creates upper level shear that suppresses hurricane production.

Sea Surface Temperature Anomalies- Oct. 17, 2015.

So El Nino can be a mixed blessing, depending on where you live.

After El Nino has run it’s course, typically in the early summer following it’s peak, a new pattern emerges: La Nina that has almost the opposite effect. Colder than normal water starts to develop in the eastern equatorial Pacific in the mid summer as the trades start raging from east to west (Peru to Asia). Strong high pressure rebuilds over the eastern equatorial Pacific while low pressure follows the warm waters being blown back towards Asia. By Christmas time the year following El Nino, the North Pacific jetstream is displaced well north, driving up towards the Aleutians into Alaska and northern Canada, and high pressure dominates the NE Pacific pattern. As a result storm and swell production starts to decrease. And the whole cycle is then set to start again.

October, 2015February, 2018

Swell Lines Magazine

The Wind Is Our Friend…Sometimes

“The wind is our friend, anyway, he thought. Then he added, sometimes.” These are the Old Man’s thoughts as he sails home after his epic struggle in Ernest Hemingway’s The Old Man and the Sea. He is describing his life as a wise old fisherman and the plight of waveriders.

Wind is the most vital variable in all of surfing and waveriders are excessively particular about its existence. Thousands of miles from our coast, we want maximum, sustained winds…over a large area, for a long time. Locally, a few days later, we desire minimal wind or maybe light wind blowing from a very distinct, offshore direction. That’s a lot to ask for and it’s the reason we cherish the days with swell and good wind.

We want this thousands of miles away…

…and this at home.

The atmospheric condition which shall not be named. The moment it is mentioned, the conditions begin to deteriorate. “Bro, its soooo glassy out here!”…then the wind picks up, onshore. “Good, the wind hasn’t picked up yet!”…the waves are textured one minute and blown out the next.

It’s a constant struggle. Its the reason we get up at 5am and blow off dinner plans in the evening. We want the best possible wind conditions. Wake up before dawn, groggily drive to your spot in the dark, check the palm fronds. Fist pump…it’s light offshore! But for how long? On average, dawn is the best time of day to surf. Diurnal, prevailing wind patterns guarantee an eventual onshore flow probably 360 days a year. Skateboarding was invented because surfers got frustrated by the afternoon onshores and looked for something to do once the surf blew out.

Each day, good conditions are fleeting. We dread the coming of the onshores. Sometimes the palm fronds and flags are pointed inland even before the sun rises. Sad face. Sometimes the wind is perfectly calm at dawn and stays that way through the morning. Sheet glass. Sometimes the wind is beautiful offshore at dawn before calming into glass through the morning. The ghastly onshores could bring the dreaded texture at 8am or 1pm…the later the better. Sometimes Santa Anas bring strong, grooming offshores all day.

The evening glassoff isn’t guaranteed but it is always anticipated. Sometimes it never comes. Sometimes the atmosphere teases a glassoff before picking up stronger onshore. Sometimes the first sets of a new swell are greeted in the late evening with perfectly calm winds and orange sunset water.

Sometimes we anticipate a swell for days. Good looking size, period and direction. Only to have it onshore at dawn and howling all day, ripping a solid swell to shreds. Other times, without expectations, a windswell will turn on super fun seemingly out of nowhere. Sometimes it’s perfectly glassy all day but the surf is double over ankle. Sometimes it’s pumping but the devil wind won’t quit. But then there are those situations we dream about and mythologize. Perfect, pure groundswell…and a light offshore breeze for days at time.

-KS

August, 2015April, 2017

Swell Lines Magazine

Breeze and Gale: The Science of Wind

Simply look at a flag and you can reckon one of the most important surf factors. If it’s pointed toward the Ocean or hanging slack, quicken your pace towards the sea. It has an enormous impact on our daily surf conditions, and in fact it is mostly responsible surf’s existence. Moving air. We call it wind. The creator and sometimes destroyer of our waves.

The Earth’s atmosphere is roughly 60 miles of gases that surround the planet. If Earth were the size of a classroom globe, the atmosphere would only amount to a couple layers of paint. Composed mostly of nitrogen and oxygen, the atmosphere is held in place by Earth’s gravity. We live and surf in the very base known as the troposphere.

Atmospheric pressure is the measure of how much air is pressing down on a given region on Earth’s surface. The movement of air from areas of high pressure to areas of low pressure is the primary cause of Earth’s surface winds. The Sun heats the Earth unevenly, so the atmosphere always contains different temperature gradients. As air molecules lose energy, they cool down, becoming more dense and sink through the atmosphere. As air molecules gain energy, they heat up, becoming less dense and rise in the atmosphere. This flow is called convection and its happening all around all the time.

Strong low pressure with surrounding areas of high pressure over the North Pacific. Image: NWS — Strong low pressure surrounded by areas of high pressure over the North Pacific. Image: NWS

Atmospheric convection creates the high and low pressure that we associate with our weather. As the warm air rises, the pressure on the surface drops. When cool air descends, the pressure on the surface increases. High pressure generally brings clear skies, light wind and stable weather. Low pressure generates precipitation, strong winds and unstable weather.

When the pressure drops, air rushes in and wind speed increases as the atmosphere attempts to find equilibrium. The rotation of the Earth causes the wind to also move in a circular pattern. Counter clockwise in the Northern and clockwise in the Southern Hemisphere: this is called the Coriolis effect.

When air moves over water, the water’s surface is disturbed. A phenomenon known as capillary waves are formed. These ripples begin the swell generating process. Gravity pulls the ripples downward but they also provide extra surface area for the wind to transfer energy into the water.

As stated before: the stronger the wind, the bigger the area (fetch) and the longer they blow- the bigger the swell. Wind speed is measured by the Beaufort Scale: from calm- breeze (4-30mph)- gale (31-63mph)- storm (64-72mph)- hurricane (72mph+). With extreme low pressure at their core, hurricanes and tornadoes contain the strongest winds on Earth, sometimes measured between 200-300mph! The planet Neptune has the strongest known winds in the solar system at 1,300mph+. Imagine the swell that would generate!

Prevailing winds are the predominant day to day winds of an area. In general, westerly winds blow across the mid-latitudes and easterly trade winds blow across the tropics. Hawaiian trade winds act like a big air conditioner for the whole island chain. Blowing from the northeast, they blow gently offshore to many famous beaches on the north coasts of the Islands. Kona winds develop from the south when the trades slow down. They often lead to muggy hot weather and volcanic fog (vog) blowing in from Kilauea on the Big Island.

Sea Breeze and land breeze Image: ncsu.edu — Sea Breeze and land breeze. Image: ncsu.edu

Diurnal temperature variation is responsible for the daily land and sea breeze cycle that impacts many coastlines across the globe. Offshore at first light, perfectly glassy at 9am, onshore- blown out by noon and glassing off as the sun sets. The Ocean remains a more consistent temperature than the land during the day-night cycle. The gradient between land and sea temperatures decreases at night as the land cools down. Land breezes, blowing from the land to the sea, accompany many mornings with favorable surf conditions. As the sun rises and heats the land more than the water, the temp rises and pressure decreases over the land. The sea breeze picks up as air moves from the water to the land, frequently blowing out and negatively impacting surf conditions. As the sun sets, the land cools down and the evening glassoff can occur.

As coastlines vary, so too the wind’s impact on different surf spots. Nicaragua is known for all-day offshore winds because Lake Nicaragua sits just 10 miles inland and keeps the land breeze blowing most of the day. Regions with bending coastlines can be a blown out mess at one spot while around the corner is offshore. Protected coves can shelter surf spots from wind. Areas with large kelp beds are less impacted by afternoon onshores because the kelp cuts the wind and smooths the sea surface outside the lineup. Katabatic winds, meaning “downhill,” like Southern California’s Santa Ana winds can change the pattern for days at a time. When fire-free, Santa Ana, offshore winds meet swell at the coastline, SoCal waveriders rejoice.

-KS

Sources:
National Center for Atmospheric Research
United Kingdom Meteorological Office
NOAA

February, 2015February, 2018

Swell Lines Magazine

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