Fuerteventura, where it is

On the island of Fuerteventura, the climate is very mild and almost desert. Along the coast the annual rainfall amounts to less than 200 millimeters (8 inches) per year, most of which occur from October to March. Unlike other islands of the Canaries, in the interior of Fuerteventura the altitude reaches only 600/700 meters (2,000/2,300 feet), too low to cause a significant increase in precipitation on the slopes exposed to the wind.
Here is the average precipitation of Puerto del Rosario.
Fuerteventura - Average precipitation

The temperature in Fuerteventura is very mild, spring-like much of the year: during the day it ranges from 21 °C (69 °F) in January to 27/82 °C (81/82 °F) in the period from July to September. Moreover, temperatures generally tend to stay around the average, except when the wind blows from Africa, which can raise the temperature by several degrees.
Here are the average temperatures.
Fuerteventura - Average temperatures
Min (°C)151516161719212221201816
Max (°C)212122232426272828262422
Min (°F)595961616366707270686461
Max (°F)707072737579818282797572

The island is particularly exposed to the northeast trade winds, which blow steadily throughout the year, especially in the afternoon. The waves that are generated by the wind are particularly appreciated by surfers.
However, as mentioned, a hot and dry wind from Africa can sometimes blow, which can reduce visibility, carrying dust or sand from the desert, and can cause an abnormal heat, which typically lasts two or three days; this phenomenon has become more frequent in recent years. Being close to Morocco, Fuerteventura is particularly exposed to these hot winds, together with nearby Lanzarote. The highest records so far have been 37/38 °C (99/100 °F) in April, May, September and October, and 41/43 °C (106/109 °F) in June, July and August.
The sun in Fuerteventura shines all year round, however, in addition to the low pressure systems that may pass over the island during the October to March period, in summer cloud banks can form on the Atlantic Ocean and reach the island. On the northern coast, and especially on the hill slopes exposed to the north, local clouds and mists can form. The south coast is therefore the sunniest one.
Here are the average daily sunshine hours at the airport, on the east coast.
Fuerteventura - Sunshine

Owing to the cool Canary Current, which flows in the ocean to the west of Morocco, the sea in Fuerteventura is cool: the sea temperature ranges from 18 °C (64 °F) in February, March and April, to 22 °C (72 °F) in the period from August to October. This means that you can try to swim even in winter, at least if you are not sensitive to cold, while in summer the sea is still a bit cool.
Here are the average sea temperatures.
Fuerteventura - Sea temperature
Temp (°C)191818181920212222222120
Temp (°F)666464646668707272727068

Fuerteventura, beach

Best Time

Typically, Fuerteventura is appreciated for beach tourism and surfing, therefore, on the understanding that owing to the mild climate you can go all year round, the best time is from May to mid-October. For the low rainfall, however, after all the island lends itself to this type of activity also in the second half of October and in November, when the sea is still relatively warm, although the first Atlantic disturbances can bring some cloudiness and some rain, which can happen also in winter. On the other hand, in autumn and winter, Atlantic depressions can bring high waves, generated by westerly or southerly winds, which are different from the typical trade winds, and can be appreciated by surfers.

What to pack in the suitcase

In winter: bring light clothes for the day, a sweater and a jacket for the evening, and possibly a raincoat or umbrella.
In summer: bring summer clothes, but also a scarf for the wind, a light sweatshirt, a light jacket for the evening and for windy afternoons; comfortable shoes for hiking.