There are two seasons in the Galapagos. The dry, or "garua" season, which runs from July to December. "Garua" refers to the fog and mist that commonly hangs on the higher elevations during this season. The hot/wet season lasts from January through June, with March and April generally being the wettest months. The timing of the seasonal change varies somewhat and there is often a several month transition when either type of weather can occur. These seasons are also governed by oceanographic conditions. Around December, several changes occur in atmospheric and oceanic currents.
The trade winds slacken and the Intertropical Convergence Zone, the "climatic equator" that is usually located north of the geographic equator, shifts south toward the Galapagos. The slacking trade winds cause the westward flowing current to slow. This reduces the upwelling and allows warmer water to invade the region. The air warms and the inversion layer breaks down.
This allows warm air to rise to the point where rain clouds form and daily afternoon showers occur.
Even in this season, however, low elevations, particularly those in the rain shadow of highlands, receive only limited rain.
Interestingly, the highlands receive more moisture from the garua than they do from the rain
Typical water temperatures vary between the islands depending on which currents they receive.
Santiago, Bartolome and Genovesa 75 -77 deg F (24-25C)
Isabela and Fernandina 69 - 75 deg F (21-24C)
Espanola 75 - 80 deg F (24-27C)
Santiago, Bartolome and Genovesa 69 - 73 deg F (21- 23C)
Isabela and Fernandina 59 - 68 deg F (15- 20C)
Espanola 68 - 73 deg F (20-23C)