How Trade Winds affect Shore Diving

Sep 21, 2020 | General Information

Shore divers on any island should have at least some knowledge of Hawaiian weather. The more the better. In fact, for the purpose of choosing the proper dive site for the day, shore divers need to know a lot about how to interpret not only winds but currents, waves and tides. By necessity, shore divers develop expertise about trade winds. These strong and steady winds, mainly out of the east and the northeast, are the most important force shaping weather patterns in the islands.

Trade winds in Hawaii emerge from the Pacific Anticyclone, a high-pressure system that, in summer, is well developed over the eastern North Pacific. These winds maintain a fairly steady position northeast of the islands. In winter, this system is weaker and not as consistent. Trade winds can be strong in winter but don’t occur on a regular basis.

Trade winds funnel through channels between the islands, picking up speed and becoming hazardous except on the protected leeward sides of most islands. Among the strongest of these channel winds is the one in the Alenuihaha Channel between Maui and the Big Island. Another is in the Pailolo Channel between Maui and Molokai. And another of equal velocity producing high waves occurs in the Kauai Channel between Oahu and Kauai.

Kona winds usually are associated with a low-pressure system near the islands. They come from the south or southwest and almost always are accompanied by rain or stormy weather. Kona winds don’t last long but they build up seas and swells in a southerly direction. As a result, water churns up on the south sides of the islands and visibility often becomes poor. Periods of southerly swells can preclude diving on south shores of all the islands.

So what are ideal times and conditions for shore diving? Best time is when the National Weather Service forecast calls for just light and variable trade winds, between 5 and 15 mph, and seas 2 to 4 feet in coastal areas or 4 to 8 feet in channels. In January and February large surf often pounds the north and west beaches of Hawaii. Surf and swells calm down after that until about November when the first real winter storms arrive in the islands and winds bring big waves to exposed northern and western beaches.