Solomon Islands Swell Analysis
Expert Opinion: Chief Swell Forecaster Ben Macartney on the Solomon Islands’ Northern Coastline
Although the Solomons northern coastline is, at least in theory, exposed to swells originating throughout the Northern Pacific, the primary source of mid-to-large north swells is typhoons (the northern hemisphere term for tropical cyclones). Typhoons forming over the western region of the North Pacific (ie the same ones that hammer the Philippines, Taiwan and Japan) can generate powerful, clockwise wind-fields within relatively close range of the Solomons northern coast; sending in powerful, mid-period groundswells ranging from north-west to north-east in direction. These storms generally form between July and November and generally move from east to west; resulting in a transition in swell direction from north-east to north-west during their lifecycle.
SEE ALSO: TESTED – SURFING THE SOLOMON ISLANDS
What else brings the swell?
In the absence of typhoons, the northern coast is exposed to a variety of other swell-sources; including shorter period tradewind swell arriving out of the east-north-east as well as north-east to north swells arriving from mid-latitudes lows. In theory, the Solomons can also see plenty of longer-range, high period groundswells arriving off the large winter lows that form over the North Pacific throughout the northern hemisphere winter.
However, there are several constraining factors on northern hemi sources. One is the vast distances that separate the larger extratropical lows from the Solomons (usually ranging anywhere from 2500 to 5000 nautical miles away). This exacerbates wave erosion and dispersion to the extent that a 40-foot swell over the North Pacific can be reduced to a fraction of a foot by the time it makes landfall across the Solomons.
Further detracting from north swell potential is the predominant north-west to south-east alignment of the storm-track; meaning most of the swell generated is north-west in direction and thereby aimed out towards the Americas’ western coasts. Apart from typhoons, probably the most effective region for storm formation for the Solomons is just off Japan; when extratropical lows are usually still in the early stages of their lifecycles. When positioned over this region, they’re more likely to deliver powerful north groundswells within closer range of the northern coastline.
Swell blocking neighbours
Probably the most effective constraint to surf potential along the Solomons’ northern coastline is swell shadowing from Pacific island chains; specifically Micronesia to the north (officially comprised of 607 Islands) and the Marshall Islands (1156 islands) to the north-east. Although it’s difficult to quantify exactly how influential their shadowing effects are, both island chains are prolific and widespread and would substantially dilute any longer-range swells arriving from the north.
The Solomon Islands South Coast
The Solomons’ south swell window is bounded by Australia’s east coast and by New Zealand’s west coast; exposing it to swells falling within the directional band bounded by 187 and 170 degrees. The distance of south swell sources can range from 1500 nautical miles (generally arising from Tasman lows) to well over 3000 nautical miles (arising from polar lows migrating west to east below Tasmania and New Zealand). Like Indo, groundswells covering these distances need to exhibit long wave periods for the wave-energy to cover the distance; theoretically from 12 to 15 seconds when originating over the Tasman Sea, and up into the 15 to 20-plus second band when originating from the Southern Ocean.
There are, of course, exceptions to these aforementioned south swell rules. The development of tropical cyclones over the Coral Sea, or sub-tropical storms out towards New Zealand, can give rise to all kinds of south to south-east swells. When located within close range of the islands, the powerful clockwise wind-fields associated with tropical cyclones can generate large or extra-large, short-range storm-swell events, theoretically exhibiting a broader directional band ranging from south-west to south-east. These events are usually accompanied by strong to gale-force local winds and monsoonal rainfall – and hence are usually not conducive to quality surf.
The positive effects of tropical storms
The other consistent source of surf is shorter-period east-south-east to south-east windswell generated by trade winds that develop throughout the south-west Pacific between November and April each year. Unfortunately, the Solomons are heavily shadowed from the full effects of the trade wind belt by down-stream Pacific nations; in particular Vanuatu and New Caledonia.
In contrast, sub-tropical storms that develop over the Tasman Sea or near New Zealand are far better placed to deliver high quality swell without the kind of weather and wind associated with tropical cyclones. The Solomons’ south-east swell window is relatively narrow; bounded by New Caledonia in the north and New Zealand’s North Island in the south. However, this is a relatively active area for storm-development and hence it’s not unusual to see strong, mid-period south-east groundswells arising from lows that develop over this region.
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