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There are two
seasons in Galapagos, but climate is tempered year-around on the
equator. The "warm" season runs from January through
April with air temperatures ranging from 65° F-81° F (water
temperatures 76° F-83° F). Skies are clear, blue and
interspersed with sporadic rains. This season offers the most
pleasant weather and calm seas. It is the best season for
cruising. From May through December, the Humboldt current
predominates, cooling air temperatures slightly to between 60° F
- 72° F (water temperatures 65° F-72° F) and creating
comfortable hiking weather. Although the sea is rarely ever rough,
southeast trade winds cause the ocean to be choppier this time of
year and a misty "garua" fog may linger part of the day.
Since climate in Galapagos depends so much on shifting ocean
currents, local weather varies from year to year.
|
Average
Max. - Min. Temperature
|
|
Temp.
(°F)
|
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
|
Max.
air |
84 |
86 |
88 |
86 |
87 |
78 |
76 |
74 |
76 |
77 |
78 |
80 |
|
Min.
air |
70 |
74 |
74 |
72 |
72 |
68 |
66 |
64 |
62 |
64 |
66 |
68 |
|
Avg.
sea |
74 |
76 |
76 |
76 |
74 |
74 |
72 |
66 |
68 |
70 |
72 |
74 |
|
Avg.
rainfall |
1 |
1 |
2 |
1.7 |
.75 |
.25 |
.50 |
.25 |
.50 |
.25 |
.50 |
.50 |
|
Hours
of clear skies |
5.3 |
7.5 |
6.0 |
7.5 |
5.2 |
4.4 |
2.8 |
3.3 |
2.9 |
3.8 |
3.5 |
4.0 |
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For the newly
arrived visitor, perhaps the most striking thing about the
Galapagos is their climate. If you are expecting the swaying palms
and lush vegetation of other tropical isles, you're in for a
surprise. Darwin opens his chapter of "The Vogage of the
Beagle" on the Galapagos with the following remark: "Considering
that these islands are place directly under the equator, the
climate is far from being excessively hot." He also notes
that "Excepting during one short season, very little rain
falls, and even then it is irregular; but the clouds generally
hang low." (While it is true that the Galapagos are
generally not "excessively hot", particularly for the
tropics, they are not cool either, as daytime temperatures in the
lowlands typically reach 30° C (85° F) or higher.)
In the same
paragraph, Darwin identifies the principal reason for the
Galapagos' dry and moderate climate: "this seems chiefly
caused by the singularly low temperature of the surrounding water,
brought here by the great southern Polar current." Today,
the "the great southern Polar current" is known as the Peru,
or Humbolt Current. Carrying an enormous volume of cold water
northward from the Antarctic region, it keeps the western coast of
South America temperate and dry. As it passes northern Peru, the
Humbolt current bends to join the Equatorial Current flowing
westward across the Pacific, bathing the Galapagos in cool water.
The Humbolt current has a mirror image in the northern hemisphere,
the southward flowing California Current, which is responsible for
California's pleasant climate. Both the Humbolt and California
currents are parts of large gyres, called geostrophic currents,
separately circulating water in the North and South Pacific.
Similar current systems operate in the Atlantic and Indian Oceans
(though Indian currents are complicated by the monsoons).
There is another
reason for the peculiar climate of the Galapagos, of which Darwin
was unaware, and that is ocean upwelling. Upwelling refers
to the rise of deep water to the surface; this can occur as a
result of both current patterns and winds. Though the actual cause
is complex, a simple explanation goes as follows. As water of the
Humbolt Current turns westward, it spreads out, or diverges. Since
the water is spread out over a greater area, extra water must come
from below, or upwell, to make up the difference. A more important
reason for upwelling, however, has to do with winds and a
phenomenon known as Ekman Transport. The trade winds blow
from southeast to northwest in the southern hemisphere and from
northeast to southwest in the northern hemisphere. Thus both blow
towards the equator. However, the winds push water not straight
ahead, but at a 45° angle to the wind direction (45° to the left
in the southern hemisphere and 45° to the right in the northern
hemisphere). This is Ekman Transport, which, like the Coriolis
Force, is a result of the Earth's rotation. Thus although the
trade winds are blowing toward the equator, they push water away
from it! Once again, the divergence in surface water allows deep
water to rise to the surface. The oceans are thermally stratified,
so that the water rising from depth is colder than the surface
water. In some areas, the water temperature can fall below 20° C
(68° F), particularly west of Isabela. For most people, this is
too cold for comfortable swimming!
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