The majority of the islands of Galapagos are south of the Equator and therefore the climate there is heavily influenced by the currents of the southern hemisphere.  Darwin and Wolf slightly over 100 miles north of the equator so they are influenced by the currents of the northern hemisphere.  Even though geographically these islands are relatively close together, there are major differences in the climates.  The most notable from a diver's prospective is the water temperature.  The water temperature at Darwin/Wolf is almost always warmer than in the south and the difference can be substantial.  The water temperature at Darwin/Wolf is usually 5 to as much as 15 degrees F  (that would be 2 to 8 degrees C) warmer than in the south.  The lowest water temperature I have observed in Galapagos (which was in the south) was 62 F (16 C).  The warmest water I have observed in Galapagos (which was at Darwin) was 82 F (28 C)
The warmest water is during March and April.  The coldest water is in August and September.
PLEASE SEE General Climate conditions in Galapagos.

Exposure Suit Recommendation
We recommend you bring a wetsuit combination that can be layered.  In the south you will need a full 6 to 7 mm suit with a hood.  In the warm season you can probably get by with a full 5 mm suit.