WIND, WAVES, AND THE EFFECTS OF LANDFORMS

Guiding Principle

Wind, above all environmental variables, has the greatest impact on the paddler.  Predicting wind speed and direction, and understanding the impact they have on the texture of the sea, is essential to good seamanship.

Performance Objectives
  • Obtain useful marine forecasts predicting wind direction and speed.
  • Predict the texture of the sea based on wind direction and speed. 
  • Understand the effects of wind and waves on the kayak and how to compensate for them.

Wind: Movement of air caused by differences in temperature and pressure.

Wind Direction: where wind is blowing FROM.

Marine Forecasts for wind speed and direction
  • Weather radio/VHF
  • Television
  • Internet
  • Newspaper
  • Local knowledge – experienced mariners
  • Make your own predictions – watch the sky and the critters
NOAA Marine Weather Forecast

Wind speed (knots); National Weather Service Advisories and Warnings; General meanings for kayakers

0 – 17 knots:

  • Be aware of wind against current and local conditions.

18 – 33 knots: Small Craft Advisory

  • Beginners stay home.
  • Intermediates have their hands full.
  • Advanced looking for surf.

34 – 47 knots: Gale Warning

  • Beginners and intermediates stay home.
  • Advanced have their hands full.

48+ knots: Storm Warning

  • Read sea kayaking magazines.
  • Polish your kayak.

Squalls and T-storms less than 2 hours in duration: Special Marine Warning

  • Lightning and kayaking don’t mix well.

Local conditions can vary significantly from the weather forecast. Keep an eye on the sky; understand cloud formations. 

Thunderstorms and squalls are usually associated with approaching cold fronts. They form along the front or on a line 100 miles ahead of the front. Squall lines are usually moving at 25 knots, so gusts of 40-60 knots are not uncommon. Keep an eye on the sky, and listen to weather radio frequently.

Near-Shore Conditions

Coastal wind direction and speed can vary from a forecast. Winds blowing offshore usually veer and pick up speed. Due to Coastal Convergence, stronger winds are created.

Sea and Land Breezes

Differential heating and cooling of the land and the sea.  Afternoon onshore breezes are common in the summer along the New England Coast.  Onshore clouds forming, onshore breeze beginning. Offshore clouds dissolve, sea breeze beginning.

Funneling and Channeling

Winds take the path of least resistance. Funnel between and wrap around islands and/or headlands.   

Wind factors that generate waves

Duration – Time that the wind blows.

Velocity – Speed that the wind blows. 

Fetch – Distance over which the wind blows.

Describing Waves

  • Wave length – distance between crests or troughs.
  • Wave height – distance from base to the crest.
  • Wave period – Time for peaks to pass a point.  Gives some sense for the amount of energy in waves.

A wave's energy is proportional to wave height squared. A four foot wave has 4 times the energy of a two foot wave. A long WL and large WH = lots of water involved.

Wave Generators/Types

Wave type - Description - Example of WH and period

Wind Waves

Generated by local winds. Irregular and short-wavelength. 

2’ every 6 sec

Swell Waves

Waves get organized into larger and longer forms. Can travel thousands of miles without loosing energy.

3’ every 14 sec.

Waves caused by Currents

Waves are either stationary or move slowly upstream. Wind against current = steep breaking waves. 

Seismic Activity & Glacial Calving

Tidal waves have huge wavelengths. Waves from icebergs breaking off can capsize even big boats. 

Boat Wakes

Some can be surprisingly big.

Shallow Water Waves

When depth of water < half the WL (wavelength), swells begin to feel the bottom and slow down. As the wave length shortens, the wave height increases; the period remains the same, so the wave must get steeper.

Breaking Waves

Waves will steepen until water is 1.3 times wave height, then will begin to break. Winds & Current can vary this from 2x to .5x wave height.

Spillers and Dumpers

The way the wave breaks is determined by the shape of the sea bed. Boomers require a watchful eye, and may have an undertow. Spillers are ok for play.

Refraction

Wave over shoal slows while deeper portion continues on, Can refract up to 180 degrees. Clapotis on sheltered side. Zones of convergence (building waves) and divergence (reduced waves) on beaches due to bars.

Reflection

Like a ball off a wall. Remember water depth and wave height (WH) equation.

Clapotis

Wave pattern often created by reflected waves combining with the incoming waves, causing an area of disturbed water where wave heights can explosively spike.

Wave-Current Interaction

Waves moving against a current receive energy from the current. WL decreases, WH increases. Rapid steepening can lead to breaking. Example: a wind wave will nearly double on a 5 knot opposing current. Consider points, narrows, constrictions – called tidal races, overfalls. Study the geography.

SUMMARY OF EFFECTS ON WAVES

Opposing winds or currents will STEEPEN WAVES.
Underwater ledges or irregularities CONFUSE WAVES.
Narrow funneling passages HASTEN WAVES.
Points of land BEND WAVES.
Steep shorelines or bulkheads BOUNCE WAVES.
Shallows, exposed rocks, beaches BREAK WAVES.
WAVES AND SHORELINE TOPOGRAPHY

Waves can travel for long distances without losing any energy … until they hit something. Understand the impacts and effects of wind, shallows, various shores, tidal currents on wind and swell shape.

BACK TO OCEAN SCHOOL RESOURCES