Maui Surf Report

TIDE HEIGHTS: The tides are affected by the moon’s position, relative to the earth and sun. The earth’s rotation makes the tides move around the earth on a daily basis, which means that they will arrive at different locations at different times. The moon phase determines whether the tidal range will be big (spring tides) or small (neap tides). Springs occur at the full-moon and new-moon, while neap tides occur at first-quarter and last-quarter moon phases. Every lunar month there are two sets of spring tides and two sets of neap tides. Tide predictions are made from decades of observed data, at given locations. The data is usually given in tide charts which help mariners to anticipate the rise and fall of the water level at their location. The tidal data observation point on Maui is located at the Kahului harbor. The tide times for other areas are given with corrections to the Kahului charts.

TIDAL RANGE: Hawaii typically has a small tidal range varying from 1.5 to 2.5 feet difference from low to high tide heights.

TIDAL FREQUENCY: There are two high tides and two low tides every lunar day (approx 24 hrs 50mins). High tides and low tides are on average 6hrs12.5mins apart.

STORM SURGE: The predicted tidal heights are affected by low pressure “storm” systems that create less surface pressure, and cause higher than expected tides. Storm surge from wind-driven water piling up at the shoreline can add up to twenty feet to the expected tide level. This will, of course, be very destructive as the sea level rises above break-walls and sea walls causing the inundation (flooding) of the land.

SWELL CREATION: The waves we experience in Hawaii are the result of storms (lows) hundreds or thousands of miles away. The more intense the low, the stronger the winds and the more powerful waves that may be generated. The strong winds blow across the surface of the ocean (called a fetch), for several days generating waves that become swell. The swell travels along in the same direction as the wind that created them. Swells can travel great distances across the deep oceans without losing too much energy. Until they start to hit the shallow water near the islands. When the swell hits the shallow water it may cause the swell to turn towards shore in a process called refraction. Refraction will cause the swells to wrap around the islands and give a variety of waves.

SWELL DIRECTION: The direction from which the swell is coming is called the swell direction. It is expressed in degrees from North. 0 zero degrees is North, 90 (ninety) degrees is from the East, 180 degrees is a South Swell, and 270 degrees is a West swell. The swell direction affects the areas that the swell will hit. North facing shores will get the brunt of a Northerly swell. West facing shores will get the westerly swell etc. Other shores may get a wrap-around wave but it will be less powerful than the direct wave.

SWELL EFFECTS: The factors that affect waves are many, the direction of the waves depends on the angle (vector) of the wind that created them, then also depends on “shadowing” behind neighboring islands, then refraction (bending/wrapping), and diffraction (spreading) around the islands due to changes in water depth. Swell height is calculated by the average height of the significant Swells in the sets. Some waves will be larger than the forecast height of the waves. Swell heights and wave interval gives important information to the overall power and quality of the resulting waves. The swells will be pushed up into much higher waves depending on the shape of the shoreline that causes them to break. A steep shelf/reef or shoreline will cause the wave to gain height quickly. A narrowing bay will also intensify the wave height and power and increase the amount of surge and wave runup.

SWELL SHADOWING: The neighboring islands may shield our shores from receiving the swell. If the swells path is blocked by another nearby island we are said to be in the swell shadow. Swell shadows also come from our own headlands and shield certain beaches from receiving certain swells. When Maui receives a northwest swell it can often be blocked by Molokai and even Oahu, North easterly swell is often smaller at Kanaha Beach than Ho’okipa because of swell shadowing from the west Maui mountains and Mokolea point near Kahakuloa.

SWELL FORECASTING: Surfers and meteorologists track the storms in the north Pacific and the south pacific, that may generate a significant swell. The larger storms that persist for the longest  will create the biggest waves. A good indication of the storm’s ability to create waves is the wind strengths in the storm. Waves will be generated parallel with the isobars surrounding the storm. When the isobars are closely packed there will be strong winds, and when they are pointing at the islands, there is a good chance that a swell will be heading our way. Then there are a network of offshore weather buoys that uplink motion data to satellites. These “Waverider Buoys” relay the information to us about the size (wave height) and duration (period) of the waves as they pass underneath the buoys. Watching the buoys will tell the surfer how the swell is progressing toward the island. There are also powerful computer wave models that extrapolate the data and tell the story of how the wave motion may be anticipated. Once the waves encounter the ocean floor close to the islands they will be affected by refraction, reflection, diffraction, and interference. The computer models can predict the behavior of the waves as the pass through the island chain. There are some graphs of the island swell shadow lines, to help the forecaster predict which swells will be caught at different locations on the island. There is a swell direction model that shows the predicted effect of the islands on the incoming swell.

Wave Direction: The wave direction shows the direction from where the waves are coming from. Usually expressed as degrees from north, North is 0 degrees. northeast is 45 degrees. Wave direction is significant when forecasting because swell can become blocked by a neighboring island. Swell direction can tell you which part of the island the waves will hit.

Wave angles: Waves will turn toward shore when they get to shallow water. The process is called refraction. Waves will wrap around the islands, and headlands too. Waves that break at an angle to shore can produce a longer ride. Cross-shore waves may also produce strong long-shore currents too.

Significant Wave Height: The significant wave height is the average of the highest 33% of the waves. This gives an indication of the general size of the waves however, individual waves may be far larger than the average and may be up to two times higher than the significant wave height.

Wave Period: the wave period is the time it takes for two wave peaks to pass a fixed point. The longer periods indicate a larger more powerful swell with a greater potential to produce larger waves. Wave periods usually range from 2 to 20 seconds. Extremely large surf can be 30 to 40 seconds between waves. Tsunami waves sometimes have extremely long wave intervals of 5 to 15 minutes.

Tides and Waves: Tides will affect waves. Lower tides will bring the reef and seafloor closer to the surface. This will make the waves break earlier at a given location. Shallow water can make the waves get steeper and more hollow. Generally higher tides will create fuller waves. At very high tides some breaks will become swamped and un-ridable. Some very low tides will expose the reef and make surfing dangerous. The specific effect on your local break is best observed over time. In Hawaii , here is a small tidal variation, of a few feet between high and low tides. Hawaii has a diurnal tide, with two highs and two low tides per day.

Moon Phase and Tides: The Moons gravity creates the tides. The sun has a lesser effect on the tide. The high tide moves across the earth as the earth rotates. When the sun and moon are aligned the combined gravitational force causes a higher than normal high tide, and a lower than normal low tide. These are called Spring Tides. There are two spring tides per month. Spring tides occur during the full moon phase and new moon phase. When the moon and sun are quartering the earth their gravitational forces are competing for the tide. This causes the high tides to be lower, and the low tides to be higher. The tidal differences between high and low tides and less. This is called Neap Tides. Neap Tides happen twice a month at the first quarter and 3rd quarter moon phase.

Ocean Waves Formation: Ocean waves are usually formed by a distant wind. Usually storms generate strong winds that act on the ocean’s surface for several days. The strength of the wind, and the duration it blows have a factor on how the resulting waves will be. The area which the wind affects the surface is called the fetch. The larger the fetch, the greater the waves produced. the small waves generated by storm winds are often confused and disorganized. These waves that come from a storm are called a “sea”. The sea travels in the direction that the wind was blowing. After some distance the waves become more uniform in a process called interference and assimilation. Smaller waves are eaten by larger waves, and some waves will cancel each other out. The organized waves are then called a swell, and they travel across the ocean in a wave train. The wave train transmits wave energy through the water, But not much water itself is moved forward. The swells lie low and wide in an undulating rhythm, and they do not create much resistance as they move. This wave energy can travel across the ocean for hundreds or thousands of miles. Swell height and wave length are measured from a series of wave rider buoys. the height is an average of the larger waves in the series. The wave length when measured in time called the wave period. The time in-between two wave crests is its period. Long wave periods mean that the waves have more power stored in them.  The longer the wave period usually means that the resulting waves will be larger. Swell travels across the surface of the ocean to a depth of about half the wave height. Waves become arranged into sets. Sets are groups of waves with a pattern. Usually sets consist of some smaller waves followed by some larger ones.

Moon Phase and Tides: The Moons gravity creates the tides. The sun has a lesser effect on the tide. The high tide moves across the earth as the earth rotates. When the sun and moon are aligned the combined gravitational force causes a higher than normal high tide, and a lower than normal low tide. These are called Spring Tides. There are two spring tides per month. Spring tides occur during the full moon phase and new moon phase. When the moon and sun are quartering the earth their gravitational forces are competing for the tide. This causes the high tides to be lower, and the low tides to be higher. The tidal differences between high and low tides and less. This is called Neap Tides. Neap Tides happen twice a month at the first quarter and 3rd quarter moon phase.