Pacific Ocean

Wind, swell & tides for Pacific Ocean

NORTH PACIFIC

The North Pacific is constantly agitated by mid-latitude depressions that are more seasonal and more extreme than their southern counterparts. In winter, the ocean comes alive from October to March, as Aleutian low pressures usually start winding up in the Russian Kuril and blast across the North Pacific to Alaska. This will produce a swell train that favours centrally located islands like Hawaii, before losing some height as it propagates southwards and eastwards towards the north coasts of French Polynesia and the far-flung eastern outposts of Rapa Nui and the Galapagos.

Islands closer to Australia receive less of this swell, but long-period, powerful NW-N pulses are more likely in the Dec-Feb window for Micronesia, Marshall Islands, Fiji, Tonga, Samoa and the Cook Islands. Typhoons mainly affect the shores outlined in the East Asia chapter, but can send some W-NW swell back towards Micronesian shores. Papua New Guinea and the Solomon Islands rely on windswell kicked up by the NW monsoon between Nov and April. Hurricanes forming off Central America are another source of unreliable, off-season swell, as they arc towards Hawaii bringing rare E-SE groundswell.

The tropics belt is combed by dependable, often forceful easterly trade winds, quadrant opposed in each hemisphere by the Coriolis effect, which bends the winds towards the equator as the earth spins through its daily rotation. This is graphically illustrated by NE winds in the Northern Hemisphere islands of Hawaii and Micronesia to a decidedly SE dominance in all the South Pacific nations. Variations are rare, with a bit of wavering to the E, but it categorically means that west-facing spots are ideal for most Pacific islands while the windward east coasts get blown-out.

The North Pacific gyre spins clockwise as the North Pacific Current flows eastwards across the top before bending south into the California Current then feeds into the North Equatorial Current, which races westwards before sweeping north into the fast-flowing Kuroshio Current to complete the loop. There is an Alaskan and Aleutian offshoot plus a weird Equatorial Counter Current, which flows eastwards and in the opposite direction to the other two Pacific Equatorial Currents.

Tidal ranges across the North Pacific are usually under 2m, but they matter on shallow reefbreaks, especially when the surf is smaller. The warmest ocean water on the planet is found in the western Pacific. The Indo-Pacific warm pool (IPWP) is the largest body of warm water in the world and has a major effect on global climate as it contracts and expands in size and varies in temperature over decades.

South Pacific

Endlessly circling low pressures ply the landless waters of the great Southern Ocean, travelling from Australia towards South America, at latitudes between 35°and 60°S. These South Pacific lows are the source of most groundswells and statistics show a slightly less intense pattern than the Indian Ocean Roaring Forties or the North Pacific. Polynesia gets sprayed from April to September and the SW swells only fade slightly in the southern hemisphere summer. Many of the South Pacific islands suffer from the swell shadow cast by New Zealand, including New Caledonia, Fiji, Tonga and Samoa. This shadow doesn’t stop all the SW swell and once the lows move further east, the S and SE swells will hit these Polynesian shores unhindered. Swell direction will often be an important factor at some reef passes, so waiting for the low pressures to enter the ideal window is crucial.

The equator is no barrier and North Pacific nations will benefit from long-period S quadrant swells during their summer, particularly further east in the Hawaiian chain. Coral Sea tropical cyclone activity is the world’s least predictable, usually forming just off the SE tip of New Guinea or Queensland and then heading south in an arc towards New Zealand, despatching solid NE-E groundswell.

The dominant E-SE winds affect most of the South Pacific nations for the bulk of the year with exceptions in PNG and the Solomons, which are on the fringe of the monsoonal patterns in the northern hemisphere. The powerful El Niño/Southern Oscillation (ENSO) occurs when the E equatorial trade winds slacken, which causes changes in circulation and sea surface temperatures (SST), allowing warmer than normal water (+ 2-4ºC) to drift eastwards across the Pacific from the dateline to Ecuador and Peru. This anomaly can affect world weather patterns and happens every 2-7 years, before reverting back to normal, cooler SSTs known as the La Niña phase.

The South Pacific main circulatory currents run westwards below the equator, turning south down Australia's eastern flank, before entering the southern ocean West Wind Drift to join up with the Humboldt and bring cold water back to the equator off South America's west coast.

Ocean surface temperatures in the Pacific fluctuate noticeably depending on the El Niño/La Nina cycle. Expect maximums around the Solomons to exceed 30ºC (86ºF) and minimums down to 8ºC (46ºF) in Dunedin NZ. The offshore islands of New Ireland, PNG see the biggest daily tidal change of up to 4m, otherwise, it is micro-tidal ranges below 2m. Semi-diurnal even (two daily tides, same range) covers most of Polynesia and eastern Micronesia. Semi-diurnal odd (two daily tides, different range) describes the tides found across Hawaii, Melanesia, PNG and most of the Solomon’s, which also experiences mixed tides, meaning sometimes one tide a day and sometimes two.