The year on San Cristóbal, month by month
All the figures are Puerto Baquerizo Moreno's: 577.7 millimetres of rain a year over 119 days and 1,968 hours of sunshine. The scoring crosses three things: how much water falls, over how many days it falls, and how much light there is.
There is a Galápagos climate table that looks like a copying error. In the same grid, August shows 14 rainy days, the highest of the twelve months, and 9.8 millimetres, the lowest figure after September. March, by contrast, has 11 rainy days and 106.3 millimetres: eleven times more water in fewer days.
There is no error. These are two different ways for water to fall from the sky, and on these islands they do not coincide in the calendar. Knowing which one you get is more useful than any annual average.
01 Fourteen days and ten millimetres
The figure to fix first is the annual one: 577.7 millimetres spread over 119 days. That is little water for so many days. A temperate place with that much rain would concentrate it into some sixty or eighty days; here it stretches over almost four months of the calendar.
The breakdown explains it. From December to April, between 51.5 and 107.4 millimetres fall each month over about ten days: these are real showers, which soak and move on. From July to November, between 18.8 and 7.6 millimetres fall over eleven, twelve or fourteen days: this is drizzle, and drizzle barely registers.
Hence the headline's paradox. September is the driest month of the year by volume, at 7.6 millimetres, and still has twelve rainy days and only 151 hours of sunshine. If you travel by the millimetres, you will pick the greyest month of the year believing you are picking the clearest.
02 What the garúa actually is
The garúa is a very fine, persistent drizzle that settles over the islands during the cool season, roughly from June to November. It does not come from storms: it comes from a low layer of cloud that sits on the islands and never quite breaks.
The cause is the sea. During those months cold currents from the south chill the water around the archipelago, the air above it cools with it and condenses at low altitude. The result is a closed sky, lower temperatures — average highs of 25.6 degrees in August against 30.5 in March — and a humidity that wets without raining.
For the traveller that means an adjustment of expectations. The cool season is not the storm season: it is the grey season. It does not force you indoors, but it does not hand back the blue sky of the photographs either.
03 It does not rain below, it does above
The figures above belong to a port, that is, to sea level. As soon as you gain height, the same month becomes a different month. The garúa's cloud layer catches on the slopes and unloads there all the moisture that below is felt only as haze.
That is why the islands read by altitude bands rather than by months. The low zone is arid: lava, thorny scrub, Opuntia cacti and palo santo, which spends much of the year leafless. The high zone, by contrast, supports a dense forest of Scalesia, tree daisies that reach twenty metres.
The giant tortoises use that difference as a calendar. In the cool season, when the garúa keeps the high ground green despite the lack of rain, the adults climb; when real rain starts in December and the low zone greens up, they come down. A study with GPS loggers fitted to 17 adult tortoises recorded journeys of up to ten kilometres, and found that almost all adult males climb, only some of the females, and none of the young.
04 The water behaves the other way round
The sea follows the same inverted scheme. In the warm season, from December to May, the water warms, the ocean is calmer and visibility below the surface is high. In the cool season the water drops to around 19 degrees, the trade winds strengthen and the surface roughens.
Visibility drops too, and for a reason worth understanding: the upwelling of cold water brings nutrients, the nutrients trigger plankton and plankton clouds the water. In other words, the water looks worse precisely because it is more alive.
So the two seasons cannot be ranked better and worse without saying for what. If what you want is to swim in comfort and see a long way underwater, the warm season wins outright. If what interests you is the activity of the marine wildlife, the cloudy water of the cool season is what explains it.
The year's four stretches
From 51.5 to 107.4 millimetres a month, over 10 or 11 days. This is the warm season: highs of 27.8 to 30.5 degrees, a mild, calm sea, and brief downpours that leave the rest of the day clear. Also the year's wettest stretch in volume.
94.9 and 41.9 millimetres over 6 and 5 days, with 180 and 191 hours of sunshine. The only stretch that combines the year's peak light, few rainy days and a sea that has not yet cooled. Highs of 30.2 and 29.2 degrees.
From 32.5 down to 9.8 millimetres, yet rainy days rise from 8 to 14 and sunshine hours fall from 166 to 148. The least water accumulated and the least open sky of the year. Highs from 27.6 down to 25.6 degrees.
7.6, 11.0 and 12.6 millimetres, with rainy days falling from 12 to 8 and sunshine climbing from 151 to 166 hours. September is the year's floor in temperature, with highs of 25.7 and lows of 19.8; November is already another matter.
05 Where the sun is
The variable almost nobody looks at is light, and it is the one that separates the months best. The year totals 1,968 hours of sunshine, a low figure for a place on the equator. The maximum falls in May, with 191 hours, followed by April with 180. The minimum is in August, with 148.
The gap between the best and worst month is barely 43 hours, a little over an hour and a half a day, but it shows because it splits the year into two steady halves: from March to June there is light to spare, and from July to October there is not enough. In December and January, at the height of the warm season, there are 168 and 156 hours: fewer than in May, despite the higher temperatures.
There is also what does not vary. You are on the line of the equator, so the day lasts about twelve hours all year and the sun rises and sets at the same time. There are no long summer evenings or early winter darkness: there are twelve hours of light, always.
06 How to choose the month
If you can go only once and want the best crossing of everything, the answer is May: 41.9 millimetres over five days, 191 hours of sunshine — the annual maximum — and a sea that has not fully cooled yet. It is the month when the two seasons overlap in your favour.
If you prefer heat and mild water and do not mind getting wet, go between January and April. Bear in mind that February and March total 107.4 and 106.3 millimetres, and that April concentrates 94.9 millimetres into just six days: it rains hard and briefly.
And if you go in the cool season, go knowing what it is: a closed sky, 148 to 157 hours of sunshine a month, highs below 27 degrees and cold water. In exchange, the high ground of the islands is green, the adult tortoises have climbed up to find it, and the sea, though it looks worse, is at its most active. November is the month that balances that best: 12.6 millimetres over eight days and 166 hours of sunshine.
