The Science of Tropical Cyclones

Tropical cyclones are incredibly powerful and dangerous natural phenomena. Every year, coastlines all across the globe are impacted by these tempests. When the storms move toward land, heavy rain, strong wind, storm surge and tornadoes all contribute to their destructive power. Depending on location and strength, tropical cyclones are called tropical depressions, tropical storms, hurricanes, cyclones, typhoons, super typhoons, etc. Wave-riders have a strange relationship with tropical cyclones. We know their power but enjoy their wave energy. Let’s look at the cyclogenesis of these storms. 

The location and naming conventions for tropical cyclones. Image: NASA
The location and naming conventions for tropical cyclones.        Image: NASA

The sun warms the tropical Ocean and delivers radiant energy to its surface. Wind blows over the water, it evaporates and ascends energetically into the atmosphere.  The rising moisture condenses into towering thunderheads. Air rushes upward and the atmospheric pressure in the center drops. This is a thunderstorm.

saffir-simpson-smAn organized group of thunderstorms that persists for 24 hours is called a tropical disturbance. When winds exceed 30mph, it becomes a tropical depression. The Earth’s rotation (coriolis effect) drives wind around the warm core of the storm. For the storm to continue to strengthen, it must remain over warm water and encounter minimal wind shear. This is when vertical winds slant the storm, dispersing the heat over a larger area, degrading the storm. Without wind shear, the cyclone remains upright and continues to develop.

When winds reach 39mph, the cyclone becomes a tropical storm and meteorologists give it a name. At 74mph, the storm becomes a hurricane. Hurricanes are characterized by a defined eye and strong low pressure in the center. Around the eye is the eye wall, an area of intense thunderstorms and the storm’s strongest wind. The Saffir- Simpson Scale rates hurricanes based on wind speed. From Category 1, 74-95mph to Category 5, >155mph. Category 3, 4 and 5 storms are deemed major hurricanes with the most dangerous conditions.  

A tropical cyclone is a heat engine, fueled by the temperature gradient between the warm Ocean surface and the cooler upper atmosphere. Heat becomes motion as the warm, moist air rushes upward and is replaced by surrounding air.Hurricane-en.svg

There are many meteorological resources devoted to studying and predicting the path that a hurricane will take. There are lives and communities at stake. Wave-riders also take a particular interest in hurricane forecasting because the path of storm is a very important aspect of it’s swell generation. Although, tropical cyclones have strong winds, they lack the size and fetch of their extratropical cousins that generate 15-20+ second groundswell. Hurricane force winds might extend 100 miles from the eye and gale force winds another 300 miles beyond that. For ideal swell impact, a tropical cyclone will slowly move toward land, strengthening as it moves but turn away or dissipate before making landfall.

Origin of our North America's tropical cyclones. Image: NOAA
Origin of our North America’s tropical cyclones.         Image: NOAA

North America is impacted by two distinct tropical cyclone regions: the North Atlantic and Northeast Pacific. Interestingly, it is hypothesized that cyclones in both originate from the same phenomena. African easterly waves are disturbances in jet stream flowing off Saharan Africa. They can develop into tropical storms in the warm Atlantic or continue across the Caribbean and Central America without development. Reaching the tropical Pacific, the disturbance can develop into a tropical cyclone using the warm water off the coast of Mexico and Central America as fuel.

North America hurricane tracks from 1958-2011.  Image: NOAA
North America hurricane tracks from 1958-2011.        Image: NOAA

NOAA Hurricane Research Division
Cyclone Center



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 atmosphere from space. Image: NASA
The atmosphere from space.     Image: NASA

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.  

Capillary waves.
Capillary waves.

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.

Image: James Brown- East London
Image: James Brown- East London

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!  

Trade winds on the North Shore of Oahu
Trade winds on the North Shore of Oahu.

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:
Sea Breeze and land breeze.            Image:

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.

Santa Ana winds can create magic.
Santa Ana winds can create magic.


National Center for Atmospheric Research
United Kingdom Meteorological Office

Spilling, Surging, Plunging: The Science of Breaking Waves

Photo: Adrian Ramirez Lopez
Photo: Adrian Ramirez Lopez

Breaking waves. We fantasize about them. We chase them. We ride them. We mythologize them. But we often overlook the incredible forces that create them. Why do waves break? One allure of riding waves is the unpredictable nature of their breaking. We can study Oceanography to understand the mechanics. We can dedicate ourselves to a spot for years, knowing it’s every mood. But no two waves are exactly the same. At the same spot, during the same swell, even within the same set. There are many forces acting to move water in that beloved motion.

The energy comes from far away; thousands of miles of open Ocean. Differences in atmospheric pressure push air in an attempt to equalize. Wind transfers kinetic energy into the water forming surface gravity waves. They propagate and organize as they travel through the Ocean as swell.

Oscillating wave energy.
Oscillating wave energy.

The waves of energy oscillate through the water, returning each particle back to where it started. Water molecules are spun in place without traveling with the wave. But when the energy approaches shore, gentle wave motion becomes violent water motion. The energy reveals itself, modeling the breaking wave after the bottom contours or bathymetry of the beach.

Photo: “Wind Waves at Sea Breakers and Surf” U.S Naval Oceanographic Office 1947

The process of the wave base slowing down on the Ocean bottom is called shoaling. Long period swell energy travels deeper in the water so it shoals before shorter period swell. Because waves usually approach land from an angle, known as swell direction, one part of the wave feels bottom before the rest. Waves always bend and refract toward shallower water. This causes waves to wrap around pointbreaks and focus energy onto shallow reefs and sandbars.


According to NOAA, “Wave steepness is the ratio of wave height to wavelength and is an indicator of wave stability. When wave steepness exceeds a 1:7 ratio; the wave typically becomes unstable and begins to break.” Wavelength is the distance between wave crests. A 2 foot wave with a 16 foot wavelength has a 1:8 steepness ratio and will not break. But as the wave shoals and wavelength decreases, the ratio changes causing the wave to break.


Oceanography textbooks list definitions for three types of breaking waves. Surging breakers rush up a very steep beach without dissipating much energy in the beach layer known as swash. Some of the energy moves back to sea, often appearing as backwash. Spilling breakers move along gradually sloping bottom contours. The crest spills down the wave face.

A Plunging breaker moves toward a steep beach, the energy spinning at the bottom of the wave feels the bathymetry. The base of the wave slows down as the crest forms upward and continues to spin.  The wave front becomes concave as the trough forms below and the crest thrusts forward.  The spinning energy completes its cycle, forming a cherished hollow wave.

Pipeline spilling out the back and plunging on the inside.
Pipeline spilling out the back and plunging on the inside.

Many of the world’s best waves are dynamic combinations of these textbook principles. Pipeline spills at 2nd Reef before the ultimate plunge at 1st Reef. Because of reflection off the jetty, Wedge can be pure chaos: surging, backwashing, plunging and dumping waves coming from every angle. Point breaks often spill for multiple sections before plunging through fast, hollow sections. Beachbreaks are especially variable; constantly changing depending on tide, wind, swell direction and sand movement.

Tide changes can alter the type of waves on many beaches. Lower tides might focus the energy in shallower water, creating plunging waves. While deeper tides can create softer, spilling waves. Many of the world’s best shorebreak waves prefer higher tides that create a combination of surging and plunging breakers on steep beaches.

Offshore wind blowing into the barrel of a plunging breaker.
Offshore wind blowing into the barrel of a plunging breaker.

Local winds also impact breaking waves. Onshore wind can prematurely blow the crest over, creating a spilling wave. Offshore wind blows up the face of a wave, suspending the crest in a rainbow of spray and holding open the plunging barrel.

After their long journey through the open Ocean, waves show their true glory when shoaling and breaking onto the beach. Much of the energy is transferred kinetically into the sand or reef, some oscillates back to sea. The remaining energy is released as that familiar sound with the formation and popping of millions of bubbles.

Oscillation beneath a breaker. Photo: Adrian Ramirez Lopez
Oscillation beneath a breaker. Photo: Adrian Ramirez Lopez

Breaking waves have an enormous impact on the Earth. They perpetually change our coastlines through weathering, erosion and deposition. They are dangerous and destructive. They sink ships and take lives. But when we swim into a breaking wave, locking our bodies into the spinning energy, nothing is more exhilarating. Bodysurfers chase weird, bending, hollow, plunging waves. We seek the shoaling, spinning forces and strive to feel the changing steepness. All of these forces focused on the seafloor below us:  truly a blessed experience!

NOAA Glossary
SECOORA Waves Glossary
Environmental Oceanography by Tom Beer
Descriptive Physical Oceanography: An Introduction
Wind Waves at Sea, Breakers and Surf” U.S. Naval Oceanographic Office 1947

Purple Blob Report: Winter 2013/2014

Polar Vortex- NASA
XXXL North Atlantic- StormSurf
XXXL North Atlantic- StormSurf

The winter of 2013/2014 is already historic. Bitter, record-breaking cold and snow seized much of the Eastern USA as the “Polar Vortex” dipped south. Sunny skies have California bracing for drought repercussions. XXL after XXL storm churned across the North Atlantic and pounded Europe. They’re calling it one of the best seasons in hypothermic New Jersey surf history.  Gerry Lopez called it a “once-in-every-30-years Pipeline season.” Let’s review the North Pacific winter and what it provided for California wave-riders.

Looking back, there were a couple of solid South Swells in June 2013. Then the Ocean went painfully dormant for much of the summer into fall. Only one beloved Santa-Ana wind/combo swell event in early October and a moderate swell for Thanksgiving. By December, California surfers dried out and moved onto secondary hobbies. NPAC season started slow. Persistent high pressure off the western US spun the storm track north.  The Ocean stayed quiet and mountain slopes remained dry.  There was a small pulse before the Holiday but it was generally pretty weak.

Early January
Early January

2014 dawned with hope as the NPAC showed signs of life. The jet stream coming off the Asian continent strengthened, unsettling the atmosphere in the Pacific near Japan. Low pressure systems started to churn across the Ocean. The high remained along California, but the swell energy from the NW began to funnel down the coast. Sunny and mostly glassy conditions met the first swells of the year. After months of sluggish surf, wave riders deeply appreciated the Ocean’s power.

NPAC-  Jan. 21st
NPAC- Jan. 21st- StormSurf

The first major swell event of 2014 began in mid January.  The North Pacific storm track exploded with activity. Successive storms moved over each other’s aggravated path and strengthened. Culminating in a multi-week run of surf for California. The final storm of the train was the biggest and most powerful. The Mavericks Invitational ran on Friday the 23rd in 25ft, wind-affected surf.

January 25th
January 25th

Long-period, WNW swell began filling into Southern California on Friday afternoon. By sunset, winter magnet waves were well-overhead and pulsing. Saturday the 24th dawned with off-shore wind and pumping 8-12ft. groundswell. The wind slacked around 10am, creating glassy, near perfect conditions that lasted all day. First light Sunday: offshore and holding swell. It remained overhead and glassy through Monday the 26th. Wave riders licked their wounds, recalling the beatdowns and glory that come with 4 days of pumping North Pacific winter energy.

SoCal Winter Weather
SoCal Winter Weather

February remained active with fun size surf throughout. Then in late Feb, a low pressure system intensified as it passed to the NE of Hawaii. The aforementioned high pressure was no longer blocking the coast. SoCal meteorologists became very busy. Weather forecasts called for a major winter storm to impact the coast. The intense low pressure tracked south and surf forecasts quickly jumped. Wind and rain began in earnest on the morning of Friday the 28th.

NPAC Energy
NPAC Energy

On Saturday morning, March 1st, the surf was waist high and windy.  The Ocean changed around noon. Rising fast, each set larger than the last. The close-proximity storm spun strong south winds, periods of heavy rain and raw WNW swell into every willing nook of coast. The Harvest Buoy peaked on Saturday at 21ft. with a relatively short 15 second period. By 3pm, most of SoCal was overpowered and decimated by wind. However, the dynamic California coast contains a few kinks that handle the south wind and pump with heavy winter energy. And pump they did!

IMG_6619  Cleanup

Sunday March 2nd
March 2nd

One San Diego giant awoke with solid 20ft. sets. While South LA was as good as its ever been: clean, double-overhead+ freight trains. The swell peaked overnight, while Sunday continued with overhead+ surf and cleaner conditions. Palomar Mountain recorded over 8 inches of rain for the storm while most areas received a healthy 3+ inches. Burning sinus membranes and the putrid smell just add to the excitement of a rainy, raw winter swell in Southern California.

Overall, the winter of 2013/2014 was good bordering on great. Characterized by a slow start then consistent energy from the W, WNW and NW, high pressure sunshine and two classic swells.

Here’s hoping the South Pacific activates and stays active for the spring/summer 2014! Looking ahead, meteorologists are beginning to see the signs of El Nino setting up for winter 2014/2015. Being a perpetual optimist, my forecast data shows pumping groundswell for the rest of forever.

Purple Blob Review
Purple Blob Review

Ode to Water

Bending Water

Hydrogen, most abundant, formed in the Big Bang. Oxygen fused in stars.
Two hydrogen atoms covalently bound to a single oxygen atom.
Dihydrogen Monoxide
Unique amongst all chemicals in the Universe.
H’s are charged positive, while O is negative.
Hydrogen bonds.
H of one molecule is attracted to the O’s of a different molecule.
Dipolarity grants superpowers:
Super solvent with cohesive surface tension.
Ice floats.
Only substance to exist naturally on Earth as
solid, liquid and gas.

Earth is the sweet spot.
If it were any closer to the Sun, the water evaporates away.
Any farther and the water freezes.
If Earth were any smaller, water would escape the gravitational pull.
Any bigger and it might be a water world…
without points or beachbreaks.

Delivered by asteroids and comets,
Water fills Earth’s holes. Shaping terrain.
Cycling up down across round and round.
Absorbing heat. Driving the atmosphere.
Controlling the climate.
Impacting everything.

Although it can be horrifyingly dangerous,
Liquid water is essential for life…
as we know it.
Facilitating photosynthesis.
Dissolving nutrients and transporting them.
Flushing toxins, regulating body temperature.
Water supports the entire Biosphere.

We drink it. Irrigate, cook and clean with it. Travel and transport on it.
We passionately use it for recreation.
From skiing to hockey, water polo to sailing.
We’ve found innumerable ways to enjoy Water.

Wherever wind blows over liquid water, waves form.
Wherever waves break, people ride them.
Whenever people ride water waves, joy is acquired.

Glorious, blessed water!
How sweet and refreshing your taste!
How unique and vital your properties!
How fun and exhilarating your energy!


Tripping Fins: Dynamic Coast

Depart Encinitas 8:30pm Friday evening: seven hours straight to Eastside Santa Cruz urban camp. Breakfast with Homeboy Eric and Homegirl Rachel then northbound to Ocean Beach, San Francisco to meet up with our buddy Dallas. Sloat St. swim: overhead and super fun. Snagged a couple solid peaks in the strong drift. Dinner and spectating in the Haight. Chat with Child: coffee shop drug dealer representing “Dead Nation.” Vibrant humanity.

Urban camp at the Pacifica Pier. Sunday 6:00am Kelly’s Cove check: not working and no orange swim cap. Back to Sloat: overhead+, catch a rip way outside. Plentiful swimming, as expected at OB. Sets on the head. Luck into a beauty of a right wall: nice speed, sensational feel.

Photo: Rachel Newton

On to FP- too much tide- Crissy Park nap. Awake to dropping tide-rising swell. The Point woke up. Thought it was novelty, discovered a legitimate wave. Head high and incredibly dynamic. Sets swing swiftly into rocks. EJ charges. Once heard a big-wave icon say he can instantly decipher who truly has the proverbial “Right Stuff” by the way they react to an approaching set…EJ is the guy swimming into the guts of It because It “looks fun.”

EJ under the bridge and dreaming.
EJ under the bridge and dreaming.
Photo: Rachel Newton

Say goodbye to dear friends. Stretch out solo. Cruise the Piers and Wharf: clam chowder and people watching.  Urban camp Stockton St. downtown San Fran. Next morning to Pier 39 for whale-watching cruise to the mythological Farallon Islands: decomposing granite monoliths 28 miles offshore. Homestead of innumerable seabirds, pinnipeds, intrepid biologists and the largest of great white sharks.

No whales today but more than my money’s worth. The reefs at Indianhead and Mirounga Bay firing with 8-10ft of raw NW Ocean energy. Apparently never ridden…the last California wave frontier. It’s out there, if you want it bad enough.

Mirounga Bay- Farallon Islands

Our vessel, The Kitty Kat looks like a plague cruise. Seasick zombies stumble to the “Ralph” spot and unload, immobilized by sheer misery. Make new friends: literature teachers from Paris: Ocèane and Aurelie. They didn’t have much fun on the cruise, but we made plans to discuss Rimbaud and Sartè later in the week. Drive over the Golden Gate to the Marin Headlands…overlooking everything. Stunning views abound.

Big Set
Big set from the Marin Headlands through binos.
Dynamic City
Dynamic City

Next morning to Point Reyes National Seashore. San Andreas Fault heartland. Exposed to North Pacific fury like few places in California. Steep blowing sand shorebreak at South Beach. Double overhead+? on the outside…head high warping wedges on the sand. Chilly swim, washed down the beach, exhilarating wompy visions. Cruised the dairy farms way out to the Lighthouse and Chimney Rocks. Fascinating physical oceanography.

Point Reyes
Point Reyes National Seashore

Southbound down iconic Route 1 back to the city. Muir Beach sunset. Quick stop back to Fort Point.  Dirtbag shower in the bathroom before meeting up with new friends from France. Found them perusing the poetry at a classic Beat bookstore.  Intellect and cute French accents make for a late night.

Urban camp Pacifica Pier…rocked to sleep by shorebreak energy. Next morning southbound, hike to the Boneyard and pay homage to Mavericks. On to Santa Cruz. A little nook is working on the Westside- waves bounce off the backside and wedge into fast hollow peaks…super fun. Watch The Point get torn apart by a heavy Westside crew including Flea and Nat Young.

Nat Young- Steamer Lane

South to Big Sur’s golden sunset light. Camp: Ocean front forest service road. Glorious dark skies…”What’s that glow in the West?” WOW! The Zodiacal Light!  First observation, been looking for years. Dust in our solar system reflecting light…beautiful!  Morning at head high Big Sur reef.

Big Sur Gold
Big Sur Gold
The Zodiacal Light
The Zodiacal Light

Southbound: Incredible wave potential everywhere. NW swell lingers. Every turn-out offers dynamic new potential. Epicness awaits the extra hearty. Somewhere: big lefts slab over an abrupt rocky reef…mindsurf. The giant elephant seals swimming on the inside have the best view.


Southward. Cayucos is offshore and amazingly walled down the beach…400 yard cylinders. Swim out but avoid the guy getting barreled on a jetski. Pushing South into Morro Bay: volcanic plug geology and peregrine falcons. Camp: Pismo Beach, Oceano Dunes. Put the Tacoma back on sand where she belongs. Sandy sweet sleep.

Central Coast
Central Coast

Headed South early. Straight to SB: to spy enchanting spinners.  Glassy, stomach high turbines roping along the breakwall. Best barrel view in California? SB framed by the Santa Ynez Mountains. Top of the list to score solid. On to the Queen. Glassy, waist to chest and hollow at the Rivermouth. Magic point…everyone should have one in their front yard.

The barrel looks out to a mountain range.
The barrel looks out to a mountain range. Santa Cruz Island out the back.

To Oxnard with the wind and fog. Cool town and I didn’t get punched in the face…bonus. Down the 1 through the wave potential of Pt. Mugu. Here the coast changes. No more secret nooks, not much open space…masses of concrete from here to Baja.  Stop at Surfrider Beach, fogged in but can see knee high waves peeling across First Point.

Dynamic coast, excellent adventure!