Swell Maps – Sources of Swell

SOURCES OF SWELL
The North Pacific: This is the breeding ground for Costa Rica’s west and northwest swells with medium to long swell periods (14+ seconds). Storm activity drops down from the Arctic Ocean over the North Pacific between November and March, with the peak storm months generally between December and February.

Occasionally, the remnants of a typhoon in the western Pacific will merge with a North Pacific storm coming off Siberia. The mixture of cold air with warm tropical air in this type of weather system can develop a super-charged extratropical storm with hurricane force winds and huge seas in the Central Pacific, resulting in a substantial west or northwest swell for the entire Pacific West coast of North and Central America—sometimes as early as October.

The Pacific Tropics off Central America and Mexico: This area fuels a number of hurricanes and tropical storms between June and October. Tropical swells are also typically short-period swells (9–13 seconds) due to the limited size of the storms. Most of the tropical storm development also occurs to the northwest of Costa Rica off the Mexico coastline. As a result, tropical swells that may arrive on the Pacific coast of Costa Rica are generally from the weaker, leading edge of the storm as it moves away from the coastline, and therefore are not a good wave source as the swells usually greatly weaken before they arrive at the coastline. The only rare exception may be a big, stationary hurricane located off the coast of southern Mexico that could generate a larger mid period swell from the west/northwest.

The South Pacific: Down in the Southern Hemisphere, the South Pacific is the primary source of long period swell (16+ seconds) for Costa Rica, averaging about 80 south and southwest swells of various sizes each year. Storm activity is active all year long in the Roaring 40s and 50s, located between 40–60 degrees south latitude. This is a major swell-generating area between Australia and South America, which extends all the way down to Antarctica. Most of the larger swells for Costa Rica are generated between March and October as the South Pacific storm track shifts northward off the Antarctic ice and focuses more swell energy up toward the Pacific West Coast of North and Central America.

The peak of the Southern Hemisphere swell season for Costa Rica is generally in the late spring for three reasons: 1) it’s still fall in the Southern Hemisphere, and the ice pack is minimal, which allows more fetch over the ocean for the winds to blow, 2) warm air from the remnants from tropical typhoons drift south in the fall and merge with cold Antarctic storms to develop super-charged extra-tropical storms. That means stronger wind speeds and bigger swells, and 3) the tropical air moving south and merging with the Antarctic storms help to shape the storm fetches in a more “north-south” orientation, which aims more swell up toward Costa Rica.

Tropical Caribbean costa Rica: The primary source of swell for the Caribbean side of Costa Rica is the northeasterly trade winds throughout the Caribbean Sea. The prime months are late November through March when the high pressure ridge over the Gulf of Mexico shifts further south to squeeze more velocity into the trades. This trade wind belt extends more than a thousand miles from Puerto Rico and the Leeward Islands all the way to the other side of the Caribbean Sea to Costa Rica, Nicaragua, and Panama.

Between the months of May through October the trades weaken as tropical waves begin to sweep through the Caribbean, some developing into full fledged hurricanes especially in June through August. These are also the rainy months with variable winds and unstable conditions on the Caribbean side of Costa Rica so the tropical swells during this period are usually not very good.

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