When to Go, Destination by Destination

There is no volcano season. Volcanic destinations sit in every climate zone on the planet, from Iceland at 64 degrees north to Rinjani eight degrees south of the equator, and the things that ruin a visit are different in each one.

In Java it is rain, and the difference between the wettest and driest month is a factor of twenty. In Iceland it is daylight: Reykjavík gets about twelve and a half hours of sunshine in the whole of December and 183 hours in July, while the rainfall barely moves. On Etna it is altitude, and the mountain runs a summer and a winter season simultaneously at different heights. In New Zealand the whole thing is inverted, and the coldest month is also the wettest, which is not true in the Mediterranean.

So the useful question is not when should I go. It is which of these places agrees with the dates I already have. The grids below are how we check.

The Italian and Greek volcanoes have a summer problem at sea level and a winter problem at height, and on the same mountain those can be the same day. Catania averages 35 °C in August while the ground at 2,900 metres on Etna is around 13 °C, with the overnight minimum at freezing. Twenty-two degrees, one cable car.

These get grouped together and they should not be. The Canaries are subtropical and close to seasonless, with Lanzarote receiving about 101 millimetres of rain in a year. The Azores are in the middle of the north Atlantic and have a real winter, with São Miguel going from 26 millimetres of rain in July to 153 in December.

The Azorean constraint is not rain, though. It is cloud height. Humidity climbs from around 80 per cent on the coast to over 90 above 400 metres, and the famous viewpoint over the Lagoa do Fogo sits at 949 metres while the lake is at 575. You are looking down from above the cloud base for much of the year.

Tropical volcanoes barely change temperature across the year. What changes is rainfall, and it changes enormously. Malang, the reference station for Bromo, records around 350 millimetres across 21 rainy days in January and 15 millimetres across a single day in August.

That matters more here than anywhere else, because the product is a sunrise. You get up at two in the morning, drive an hour, walk in the dark, and either there is a view or there is grey. In the wet season it is mostly grey.

Costa Rica deserves a warning of its own. The familiar rule that December to April is the dry season is a Pacific rule. It holds for Guanacaste and the Central Valley. Arenal sits on the northern, Caribbean-facing side and has no true dry season at all, which is why a single seasonal line for the whole country sends people to Arenal at the wrong time.

Two different logics here. In the far north the season is made of light, not weather: Reykjavík's rainfall varies from 95 millimetres in December to 43 in May, which is nothing, while daylight goes from four hours to twenty-one. May is also the sunniest month of the Icelandic year, ahead of July, and one of the driest, which makes it the best value month on this page.

South of the equator everything inverts, and not only by six months. In New Zealand winter and rain coincide, where in the Mediterranean they are opposed. Rotorua's July is both the coldest month and the wettest.

You have the dates. Which destination agrees with them?

A monthly average does not describe your week. The March figure for Vík in Iceland has ranged between 55 and 417 millimetres in different years. The mean is a real number and no individual March has ever looked like it.

Altitude beats the calendar. Every reference station in these grids is lower than the attraction it describes, sometimes by three thousand metres. Air cools by roughly 6.5 °C per thousand metres, so a coastal reading tells you what the airport felt like, not the crater.

Cold air pools in calderas. The simple altitude correction actually underestimates how cold a caldera floor gets before dawn, because cold air slides downhill and settles. Bromo's sand sea gets frost on nights when the arithmetic says four degrees.

The dry season is also the cold season at altitude. Clear skies radiate heat away overnight. The months we recommend for Acatenango are exactly the months with the coldest nights at 3,600 metres, which is why the packing advice matters more in the good season than the bad one.