The question always arrives the same way: «when is the best time?». With three destinations in three different hemispheres the short answer is that it depends which one, and the medium answer fits in three paragraphs.
Zanzibar · June to October
This is the window the island has marked as its best. The thermometer is not what decides it: the temperature moves between 25 and 32 °C right through the year, so nobody goes to Zanzibar for the heat — the heat is always there.
There is a second calendar that matters more than the annual one and that almost nobody checks before booking: the tide. On the east coast the water withdraws hundreds of metres and comes back six hours later, so the hour for swimming changes every day. It does not decide the month; it decides the morning, which is what actually gets remembered.
From Madrid it is about twelve hours with one stop, which means the journey eats a day at each end. With less than a week on the island it does not pay off.
Hội An · February to May
The good window on the central coast of Vietnam is a different one and does not overlap with Zanzibar's: February to May. The temperature runs from 22 to 30 °C through the year — a degree cooler at the bottom than the Indian Ocean and a little lower at the top.
What makes the date matter here is not only the beach: the old town is twelve minutes away and is walked rather than driven, and walking a city is not the same in every month. Anyone going mainly for Hội An should look at the calendar more carefully than someone going mainly for the sand.
Lanzarote · all year round
This is the odd one of the three: the island has no bad season. The annual band runs from 18 to 28 °C, the narrowest and mildest of the three, and it explains why it works as well in August with families as in January with people escaping winter.
And there is one figure that shifts the decision as much as the weather does: two and a half hours' direct flight from Madrid. That makes Lanzarote the only one of the three where a short trip makes sense — four days are four days, not two days and two planes.
What this guide doesn't say
It does not give millimetres of rain, or humidity, or water temperature, or which week a monsoon arrives or leaves. None of that is published anywhere on this site and none of it is going to be estimated here: a season guide with approximate figures is worse than no guide at all, because whoever reads it uses it to buy tickets.
That is what asking directly is for. Every hotel knows what its coming week looks like far better than a thirty-year average does, and it answers.
