La Gomera, where it is located

In La Gomera, a small round-shaped island belonging to the Canaries, the climate is subtropical oceanic on the coasts, that is, very mild and sunny most of the year, with very mild, spring-like winters and warm, sunny summers; there is also little rainfall, concentrated in the period from October to March.
In the interior, the climate varies instead according to altitude and slope exposure: in fact, the slopes exposed to the northeast trade winds receive a moderate amount of rain and are green, while on the southern slopes, the rainfall is scarcer, often below 350 millimeters (13.5 inches) per year, to the point that the island appears to be divided in two, the northern part being verdant and the southern one semi-arid.
The prevailing winds, the northeast trade winds, make the northern slope more humid, while they temper the heat along the coasts during summer. The trade winds blow more intensely in the afternoon, when they are often moderate or even quite strong. The days of calima, characterized by abnormal heat and light wind, when warm air masses from Africa prevail, are relatively rare, and 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 inland hills, and it's 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 receive a cool breeze from the sea.

Playa Santiago, La Gomera

Along the coasts, where the largest city, San Sebastián de la Gomera, is located, daytime temperatures are very mild in winter, around 21 °C (70 °F) in January and February, and warm in summer, around 26/27 °C (79/81 °F) from July to September. Here are the average temperatures in San Sebastián, on the east coast.
San Sebastián - Average temperatures
Min (°C)161516161719212121201817
Max (°C)212121222324262627262422
Min (°F)615961616366707070686463
Max (°F)707070727375797981797572

The rain pattern is Mediterranean, which means that the bulk of the rain falls between October and March, when the Canary Islands are sometimes reached by Atlantic depressions; in summer, on the contrary, it hardly ever rains. Here is the average precipitation in San Sebastián.
San Sebastián - Average precipitation

In the interior of the island, entirely occupied by hills and mountains, the weather gets cooler as you go up in altitude. As mentioned, the north side has a cool and humid microclimate, with rains of some importance in the cold half of the year, and more frequent mists and clouds for much of the year due to the trade winds, so much so that there are several towns that are situated in a green environment. At 600/700 meters (2,000/2,300 feet), the daytime temperatures are about 16 °C (61 °F) in winter and 25 °C (77 °F) in summer.
The highest peak is Garajonay, 1,487 meters (4,879 ft) high. The area to the north of the mountain is very green, in fact, it is covered by a thick forest of laurel trees, in addition, it's home to some endemic species, and it is a national park (called Garajonay National Park) as well as a World Heritage Site by UNESCO since 1986.

View from the top of Garajonay, Mount Teide in the background

The amount of sunshine in La Gomera is very good throughout the year, however, in addition to the low pressure systems that can pass over the island from October to March, cloud banks can form in summer on the Atlantic Ocean and then affect 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 in San Sebastián.
San Sebastián - Sunshine

The sea in La Gomera 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, near the Tropic of Cancer, but in this part of the Atlantic, a cold current flows. The sea temperature ranges from 19 °C (66 °F) between January and April to 23 °C (73 °F) between August and October. Here are the average sea temperatures.
La Gomera - Sea temperature
Temp (°C)191919192021222323232220
Temp (°F)666666666870727373737268

Best Time

The best time for a beach holiday in La Gomera runs from May to mid-October. In the first period (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 or to 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.

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. To climb mount Garajonay, bring a down jacket, and hiking shoes.
In summer: bring summer clothes, but also a scarf for the wind, a light sweatshirt, and a light jacket for the evening and for windy afternoons. To climb mount Garajonay, hiking shoes, and a sweatshirt and a light jacket.