Map from Google - Lanzarote

The island of Lanzarote, the north-easternmost of the Canary Islands, has a very mild and almost desert climate, with very mild winters, and warm, sunny summers.
Along the coasts, the rains amount to less than 200 millimetres (8 inches) per year; they are due to low pressure areas that pass in the period from October to March, while in summer basically it never rains. Here is the average precipitation in Arrecife, the main city, where the airport is located.
Average precipitation - Arrecife
Prec. (mm)241415162000271227119
Prec. (in)

Unlike other islands of the archipelago, in the interior are no mountains high enough to cause a substantial increase in precipitation. However, at the highest point of the Famara massif, 670 metres (2,200 feet) above sea level, where the military station and the Ermita de las Nieves are found, the landscape is a bit greener, mist and fog can form quite often and there are terraced fields.
Temperatures in Lanzarote are very mild, spring-like much of the year: during the day and they are between 20/21 °C (68/70 °F) in January and February, and 27 °C (81 °F) in August and 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 - Arrecife
Min (°C)141415151618202120191715
Max (°C)202122222425272727252421
Min (°F)575759596164687068666359
Max (°F)687072727577818181777570

The island is heavily exposed to the trade winds, winds that blow constantly throughout the year, from the northeast, especially in the afternoon. The waves generated by these winds are particularly appreciated by surfers. However, as mentioned a hot and dry wind from Africa can sometimes blow, which can reduce visibility due to dust or desert sand, and bring abnormally high temperatures, which are felt especially in the inland areas, and usually lasts one or two days.
The sun in Lanzarote shines all year round, but especially from May to September, when clear skies are the norm.

Lanzarote is a volcanic island: in the north there is the crater of Volcan de la Corona, about 600 metres (2,000 feet) high, while in the west, in the National Park of Timanfaya, we find the Fire Mountains, where the landscape is lunar and characterized by craters, calderas, geysers, caves (cuevas), and soil made of volcanic rock, where tourists can make excursions by dromedary.

Lanzarote, Timanfaya National Park

To the north of Lanzarote we find the Chinijo Archipelago, made up of small islands (Montaña Clara, Alegranza and La Graciosa), and islets (Roque del Este and Roque del Oeste).

The sea is cool, because of the cold sea current, called Canary Current, which flows to the west of Morocco: the sea temperature ranges from 19 °C (66 °F) in January, 18 °C (64 °F) in February, March and April, to 22 °C (72 °F) in the period from August to October. So basically 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 - Lanzarote
Sea (°C)191818181920212222222120
Sea (°F)666464646668707272727068

Beach in Lanzarote

When to go

For beach tourism and surfing, the best time to visit Lanzarote goes from May to mid-October; although having a mild climate it can be visited all year round. 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 depressions can pass, bringing some cloudiness and some rain, which can happen even in winter. On the other hand, in periods of bad weather, south winds can generate high waves, which can be appreciated by surfers.

In suitcase - what to pack

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.