Climate of the South Pacific

RarotongaThe Pacific Ocean has a greater impact on the world’s climate than any other geographical feature on earth. By moving heat away from the equator and toward the poles, it stretches the bounds of the area in which life can exist. Broad circular ocean currents flow from east to west across the tropical Pacific, clockwise in the North Pacific, counterclockwise in the South Pacific. North and south of the “horse latitudes” just outside the tropics the currents cool and swing east. The prevailing winds move the same way: the southeast trade winds south of the equator, the northeast trade winds north of the equator, and the low-pressure “doldrums” in between. Westerlies blow east above the cool currents north and south of the tropics. This natural air-conditioning system brings warm water to Australia and Japan, cooler water to Peru and California.

The climate of the high islands of the South Pacific is closely related to these winds. As air is heated near the equator it rises and flows at high altitudes toward the poles. By the time it reaches about 30 degrees south latitude it will have cooled enough to cause it to fall and flow back toward the equator near sea level. In the southern hemisphere the rotation of the earth deflects the winds to the left to become the southeast trades. When these cool moist trade winds hit a high island, they are warmed by the sun and forced up. Above 500 meters elevation they begin to cool again and their moisture condenses into clouds. At night the winds do not capture much warmth and are more likely to discharge their moisture as rain. The windward slopes of the high islands catch the trades head-on and are usually wet, while those on the leeward side may be dry.

Rain falls abundantly and frequently in the Pacific islands during the southern summer months (November to April). This is also the hurricane season south of the equator, a dangerous time for cruising yachts. However, New Zealand and southern Australia, outside the tropics, get their finest weather at this time; many boats head south to sit it out. The southeast trade winds sweep the South Pacific from May to October, the cruising season. Cooler and drier, these are the ideal months for travel in insular Oceania, though the rainy season is only a slight inconvenience and the season shouldn’t be a pivotal factor in deciding when to go. Click through to South Pacific Weather for more specific information.