Seasons

The Galapagos Islands are far removed from any continent, and they are tiny themselves, so their climate is mainly defined by the currents sweeping their shores and their position at the equator. As mentioned earlier, the equator is typically a place of low atmospheric pressure, where hot air rises and is replaced by cooler air blowing from both hemispheres as the trade winds. To uncover the principles behind the fickle climate of the archipelago, we need to understand more about that area of low atmospheric pressure. In scientific terms, this area is called the Intertropical Convergence Zone (ITCZ). Sailors call it the doldrums. These are noted for the calm periods when the winds disappear altogether, trapping sail-powered boats for days or weeks.

The continents’ spread heavily influences the ITCZ’s shape. Its location varies with the seasons. Over land, it moves back and forth across the equator following the sun’s zenith point. Over the oceans, the seasonal cycle is subtler due to smaller changes in ocean temperatures. In Central America, the summer in the northern hemisphere drags the ITCZ north. Even during the northern hemisphere winter, the vast North American continent does not allow the ITCZ to drop much below the equator.

From June to December, when the Intertropical Convergence Zone sits well north of the equator, the cold Humboldt Current and the upwelling of the Cromwell Current define the islands’ climate. Air temperatures can fall to 20°C (68°F). The southeast trade winds cause the seas to become choppy. The air sitting just above the ocean surface is cooled down and gets trapped between the sea and the layer of warmer air above it. Moisture in the air condensates at the border between the layers of the hot and cold air, cloaking the tops of the islands in a mist called garúa. Despite garúa, this is a dry season with very little rain, perhaps 10 mm (0.4 in) in a month. The abundance of nutrition in the cold sea means that the marine life, and everything that depends on it, explodes with activity.

Between December and May, during the northern winter, the Intertropical Convergence Zone moves from its northern position down to the equator. The southeast trade winds slacken, and the warm waters of the Pacific Equatorial Counter Current find their way south, increasing air temperatures to above 32°C (90°F). The layers of cold air disappear, and the garúa dissolves. Increased evaporation and rising hot air result in downpours. After all, the hot and humid weather makes it feel like the islands are placed on the equator. Most plants flourish, and land animals breed.