Map from Google - Fuerteventura

In the island of Fuerteventura, the climate is very mild and almost desert. Along the coast the annual rainfall amounts to less than 8 inches per year, most of which occurs in autumn and winter. Unlike other Canary Islands, in inland areas the altitude reaches only 2,000/2,300 feet, too little to cause a significant increase in precipitation in the slopes exposed to the wind.
Here is the average precipitation of Puerto del Rosario.
Average precipitation - Fuerteventura
Prec. (in)

The temperature in Fuerteventura is very mild, spring-like for much of the year: during the day it goes from 68 °F in January, to 81 °F in the period from July to September. The 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.
Average temperatures - Fuerteventura
Min (°F)575759596164687068666359
Max (°F)687072727577818181777570

The island is particularly exposed to the trade winds, which blow steadily throughout the year, from the northeast, especially in the afternoon. The waves that are generated are particularly appreciated by surfers. Sometimes, however, there can be a hot dry wind from Africa, which can reduce visibility, carrying dust or sand from the desert, and cause an abnormal heat, which is felt especially in the interior of the island, and typically lasts one or two days.
The sun in Fuerteventura shines all year round, but especially from May to September, when blue skies are the norm.
The sea is cool, because of the cool sea current called Canary Current, which flows to the west of Morocco: the sea temperature ranges from 66 °F in January, to 64 °F in February, March and April, to 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 cool.
Here are the average sea temperatures.
Sea temperature - Fuerteventura
Sea (°F)666464646668707272727068

Fuerteventura, beach

When to go

Typically Fuerteventura is appreciated for beach tourism and surfing, so on the understanding that due to its mild climate it can be visited all year round, the best time to visit it goes from May to mid-October. For the low rainfall, however, after all the island lends itself to this type of activity even 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 even in winter. On the other hand, autumn and winter disturbances can bring high waves, generated by western or southern winds, which are different than the typical trade winds, and can be appreciated by surfers.

In suitcase - what to bring

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