Avid surfers like large waves.  Hawaii is close to the northern Pacific winter storm track leading to an abundance of high surf from October through April. Hawaii is a surfer's paradise for more reasons than just the size of the waves.  Other factors are critical too, such as wave shape, accessibility, number of surfing spots, local weather, and tides.

The shape of the wave determines the quality of the ride. The surfer desires a wave with a wide open shoulder, or blue water, where he/she can race toward safety from the steep section of the breaker where the white water hurls shoreward, better known as a "curl" or "tube".

What makes the shape of the waves so desirable in Hawaii?  Scientists call it geomorphology-- no I'm not talking with a mouthful of peanut butter, it's just a fancy word for the shape of the coastal sea floor.

The first important ocean bottom characteristic in Hawaii is the short distance from deep ocean to the breaking zones on the reefs and beaches.  The narrow coastal sea floor shelf and steep slope from deep to shallow water result in a minimal loss of wave energy prior to breaking.  This leads to "island juice"-- wave power in surfer lingo.

The second aspect of the seabed in Hawaii is the complex arrangement of underwater hills and valleys adjacent to shore. These were created by ancient lava flows, streams, erosion and extinct and growing coral reefs. Waves entering the coastal zone bend toward the shallowest areas. Scientists call it refraction.  This occurs because the depth determines wave speed in the shallow waters.

Consider a long wall of water moving shoreward toward a reef with deep water on either side.  At the shallowest location on the reef, the wave slows down.  But the wall on either side in the deep water moves ahead.  A bird's eye view would show a seaward bowed pattern of the originally straight wall centered on the “hill” or shallowest area.

At some moment in time, the wave face in the shallowest area becomes steep and unstable, causing a crest to form, then hurling forward as white water, or referred to by surfers as a “pitching lip.” The surfer begins his/her ride just seconds before the crest throws shoreward.  The surfer angles to the left or the right, depending on which side has the most desirable form and a safe exit, away from the turbulent white water of the shallower waters, toward the blue wave face or "shoulder" in the deeper waters on the edge of the reef. 

This second aspect of sea floor shape also determines the accessibility. One can safely and easily approach the take off zone by paddling in the deep, blue waters, called the channel, on one or both sides of a sea floor hill or reef, where the turbulent white water occurs.

In contrast, long sandy beach breaks found around the world, and well known up and down the east coast of the USA, have a seabed shape that is consistent in depth with distance from the beach, that is, the depth contours run parallel to shore. In these locations, there are no channels to access the surf, making it a wearisome task to punch through the breakers and reach the outside takeoff zone.

In Hawaii, with such a complex pattern of "hills" and "valleys" in the nearshore area, a large number of surf spots result.  There are hundreds of excellent places to ride waves on the north shore, with each having a favorable incoming wave direction, height, and period, or time between successive waves, that make that place "turn on and go off", surfer terms for optimal surf.

Several other geographical aspects make the surf so exceptional in Hawaii. Waves typically are generated by storms that track from Japan eastward toward California or Alaska.  This results in the most common wave direction during Fall through Spring from the northwest. The coast from Haleiwa to Kahuku on the north shore faces directly into the most frequent swell episodes, allowing greater focusing of the swell energy on the reefs and thus the highest surf heights possible for the given wave pattern.

Also, since the coast faces northwest, and the prevailing trades are from the east, the local winds blow "offshore" or against the waves, resulting in the most desirable wave form for surfers.

Tidal ranges in Hawaii are small, about 2 feet (0.6 m) during spring tides. With the small tidal variation, the surf is more consistent throughout the day. Many other big wave venues around the world are at locations with extreme tidal ranges, making the window of opportunity for the best waves even narrower.

Since the storm track is usually north of 25N latitude, and Hawaii is at 20N latitude, Hawaii typically remains in fair weather when the waves arrive, as opposed to higher latitude locations like Oregon that mostly get their biggest waves along with stormy gales, making junk surf.  The tropical latitude of Hawaii makes for the balmy, warm weather year round, ideal for “hanging loose” on the beach, and “cutting loose” in the surf.