In La Palma, the north-westernmost island of the Canaries, the climate is subtropical oceanic on the coast, that is, very mild and sunny most of the year, with rainfall concentrated in autumn and winter.
In inland areas, on the other hand, the weather becomes cooler and wetter with increasing altitude; the almost complete absence of plains makes this island moist and verdant compared with other islands of the Canary archipelago.
However, on the coast, the amount of rain that falls in a year is not very high: at the airport, it is equal to 370 millimeters (14.5 inches), most of which occurring between October and March, that is, the period when the Canary Islands can be reached by some Atlantic depressions, with a maximum in November and December.
Here is the average precipitation at the airport, located on the east coast, not far from the city of Santa Cruz de La Palma.
La Palma - Average precipitation

As mentioned, the temperatures are very mild on the coasts: highs are around 21/22 °C (70/72 °F) from December to April and 26/27 °C (79/81 °F) from July to October, as you can see in the following table.
La Palma - Average temperatures
Min (°C)161516161719212121201817
Max (°C)212121222324262627262422
Min (°F)615961616366707070686463
Max (°F)707070727375797981797572

Tazacorte, beach

In the interior, the temperature becomes naturally lower with increasing altitude: at 600 meters (2,000 feet), average maximum temperatures are around 16 °C (61 °F) in winter and 24/25 °C (75/77 °F) in summer. On inland slopes, rainfall is more abundant as well, and thick forests of pine, laurel and other species are found (on this island, there is a large biodiversity).
The prevailing winds, the north-east trade winds, cause mists and clouds on the exposed slopes, while they temper the heat along the coasts in summer; they are more intense in the afternoon, when they are often moderate or even quite strong.
The days of calima, characterized by abnormal heat and light wind due to warm air masses from Africa, are relatively rare, and are rarer in La Palma than on the eastern islands of the Canaries because of the greater distance from the African continent. However, they are more frequent in spring and summer. In practice, these are the only days when the temperature exceeds 30 °C (86 °F) and when the heat is unpleasant. The calima is also felt on the highlands, and they are often felt even more than in the plains. This happens because warm air is lighter and tends to rise, and also because the coasts can be reached by a cool breeze from the sea.
The amount of sunshine in La Palma is very good throughout the year, however, in addition to the low pressure systems that can pass over the island from October to March, in summer, cloud banks can form on the Atlantic and then reach the island. On the northern coasts, and especially on the mountain slopes exposed to the north, local clouds and fogs can form. The southern coast is therefore the sunniest one.
Here are the average daily sunshine hours at the airport.
La Palma - Sunshine

Caldera de Taburiente

La Palma is a volcanic island; the southern part of the island is covered by a ridge of volcanic craters, among which stands Cumbre Vieja, an active volcano, 1,949 meters (6,394 feet) high, while the central part is occupied by the large Caldera de Taburiente, protected in a national park.
On the edge of the caldera, we find the highest point of the island, Roque de los Muchachos, 2,423 meters (7,949 feet) above sea level. Being above the altitude where the trade winds blow, it is generally above the clouds, and this is why an astronomical observatory was built here, the Gran Telescopio Canarias; from the top you can see, scattered on the ocean, other islands of the Canaries (Tenerife, La Gomera and El Hierro). At this altitude, winter is cold, with highs around 7/8 °C (45/46 °F) and lows near the freezing point; sometimes, snow can fall, even abundant. In summer, the temperatures are mild or pleasantly warm during the day (but with a very strong sun, which requires adequate protection, like sunglasses and a hat) and cool at night.
Here are the average temperatures.
Roque de los Muchachos - Average temperatures
Min (°C)112359131410742
Max (°C)78911141823221814118
Min (°F)343436374148555750453936
Max (°F)454648525764737264575246

Roque de los Muchachos, observatory and view

The sea in La Palma is quite cold in winter, though not prohibitively, and becomes warm enough for swimming from August to October. The island is located at a low latitude, almost at the Tropic, but on this side of the Atlantic Ocean, a cold current flows, however, in this western part of the Canary Islands, the sea is slightly warmer than in the east, where the current is stronger. The sea temperature ranges from 19 °C (66 °F) between February and April to 24 °C (75 °F) in September.
Here are the average sea temperatures.
La Palma - Sea temperature
Temp (°C)201919192021222324232221
Temp (°F)686666666870727375737270

Best Time

The best time for a beach holiday in La Palma is from May to mid-October. In the first part (May-June), the air temperature is a bit lower and the sea is a bit colder, but the days are slightly longer. In the Canaries, the days in summer are shorter than in Europe (while they are longer in winter), but because of the time zone adopted, the sun sets late enough anyway.
If you want to visit cities and go on excursions to the interior, you can choose April, May and the first half of October.
In winter, you will appreciate the mild temperatures and you can often sunbathe, although we can not exclude some days of bad weather. If you want, you can combine a hike in the mountains, in search of the snow, with an afternoon at the beach.

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. When going mountain climbing, bring a down jacket, a hat, gloves, and hiking shoes.
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. When going mountain climbing, bring hiking shoes, and a sweatshirt and a jacket for the highest elevations.