Darwin notes some aspects of the local landforms that have to do with climatological conditions:
"it is a remarkable circumstance that every one of the twenty-eight tuff-craters which were examined, had their southern sides either much lower than the other sides, or quite broken down and removed. As all these craters apparently have been formed when standing in the sea, and as the waves from the trade wind and the swell from the open Pacific here unite their forces on the southern coasts of all the islands, this singular uniformity in the broken state of the craters, composed of the soft and yielding tuff, is easily explained"
– Darwin, Voyage of the Beagle, Chap. 17

Galápagos Climate:

• Relatively mild (19-30° C [66-86° F] air temperatures, 22-25° C [72-77° F] sea temperatures)
• Very dry (annual rainfall of less than 200 mm [7.9 inches])
• Two primary seasons in Galápagos:
  • January-early June: warm/wet season
    • Warmer temperatures
    • Winds from the east
    • Gentle seas
    • Clear skies, with occasional heavy rains
  • Late June-Decenter: garúa or cool/dry season
    • Cooler temperatures
    • Winds from the southeast
    • Choppier seas
    • Garúa (mist) forms due to inversion layer 300-600 m above sea level
• Highlands get more water from rain or garúa than lowlands
• Rain concentrates on southern and eastern slopes of highlands

Climatology
As everywhere, weather is controlled primarily by oceanography, and shallow oceanography (upper 1 km) is controlled by wind. So let's start with global air circulation.

Lower 10-18 km of atmosphere is the troposphere. It is warmest at the base (where warmed by land surface) and cools further up (due to distance from heat source and to expansion (decreased pressure)).

As land surface heats up due to sunlight, warm shallow air rises. Since nature abhors a vacuum, other air must come in replace it.

Since Earth's surface is curved (sphere), get latitudinal effects:

• Equator has more direct sunlight (more photons/unit area) and less atmosphere to penetrate than poles (less photons/unit area)
  • Consequently, equator is warmed more than poles
• Equator tends to gain energy (more incoming sunlight than outgoing heat), poles lose it, 40° latitude breaks even
• So, all other things being equal, air rises at the equator, sinks at the poles, and there would be one big circulation cell

However, Earth also rotates, so it generates Coriolis effects:

• Object (including air mass)moving from poles toward equator will be deflected from straight line target, due to rotating Earth
• Similarly, object from equator moving poleward would move off of intended straight line target
• Net result: deflection pattern which is clockwise in northern hemisphere, counter clockwise in southern hemisphere

In cases of air masses, combined effect of altitudinal, latitudinal, and Coriolis effects generates Hadley circulation cells.

Global circulation pattern of Hadley cells in turn drives global major wind patterns. Equator represents the convergence of the Trade Winds.

Galápagos Archipelago lies at confluence of several major currents:

• Peru Current and Humbolt (Peru Coastal) Currents: eastern parts of the South Pacific Gyre, bringing cold Antarctic water towards equator
• South Equatorial Current: northern part of the South Pacific Gyre
• Panama Current (also called Niño Flow), seasonal, off of northern South America: more on this later

Major effects: