Quito & Highlands: Quito is broadly representative of the climate in the Highlands region, and the deluge of rain is coming to an end in this part of the Andes in May. Rainfall is at its lowest average amount of the calendar year, and it's set to get lower yet, bringing on high season in the Highlands from next month. Sun is more in evidence too, and there are many completely rain-free days.
Oriente/Amazon: Ecuador's Amazon climate varies because this is a vast region but as a rule, this is one wet month, even by the standards of a very wet region! With an intense 13 inches/ 331mm of rain on average in May in places like Parque Nacional Yasuni, the region is overall experiencing its wettest month.
Desert Coastal Strip & Galapagos: Rains, which have actually been high despite the hot and sunny weather, die off in May, both on the coast and Galapagos Islands. This has some contrasting effects. On the coast, muggy, cloudy weather starts to sneak in towards the end of the month, making the coast cooler and less pleasant for beach activities. On the Galapagos, the rains are stopping too in May, but the islands are green because of all the water they have received, and despite cooler air temperatures waters remain warm and calm.
Crowds & Costs
This is widely considered the best month (alongside April) for visiting the Galapagos. However, it is far from the best month to visit the Highlands (where it's getting drier but is still not the most appealing time to visit) or the coast (where it's getting cloudy and cool). This is actually a great month for looking for deals and discounts in all regions except in the Amazon where, despite the wet weather, crowds keep coming because of the wildlife watching opportunities.
Where to Go
Quito & Highlands: In Quito, taking a trip on the TelefériQo Gondola high above the city in May yields superb, cloud-scattered views. Parque Nacional Cotopaxi has great hiking amidst snow-capped volcanoes: better weather could mean a trip out here is beautiful right now. Around Cuenca, explore the craft villages such as Sigsig or Chordeleg: indoor stores for the wet weather and good surrounding hikes for the dry.
Oriente/Amazon: This is a good month for exploring Parque Nacional Yasuni. An increasingly wet month like March means much wildlife evades the water levels and takes to the trees, so it is easier to see. The towns of Tena of Baeza, with great white-water rafting, are still perfect to visit now for water sports, although from next month water sports opportunities will decrease.
Desert Coastal Strip & Galapagos: May is a good month along the coast for doing non-beach related activities. Canoa, a town with far more than just its beaches, is a good place to linger, with a nearby organic farm, Río Muchacho Organic Farm, on which you can stay overnight and eat some of the exquisite produce.
San Lorenzo in the north, with strong Afro-Ecuadorian culture and a lively festival this month, is another interesting stop. This is one of the best months for visiting the Galapagos (along with April) because the weather, although cooler, has not yet cooled the water, the rains have dissipated and the landscapes are particularly lush.
What to Do
Quito & Highlands: It is time to get the walking boots out in the Highlands. There are superb treks to do in the mountains, such as the Quillota Loop or hikes in Parque Nacional Cotopaxi, both not far from Quito. Photography is great at this time of year, with a mix of sun, cloud and special light.
Oriente/Amazon: Once May is over, the opportunity to do white-water rafting decreases a lot, because water levels will not be sufficient. May remains a good month for exploring small Amazonian tributaries by canoe, such as those in Cuyabeno Reserve.
Desert Coastal Strip & Galapagos: It is time to try coastal activities that do not entail lying on the beach or surfing: this could be exploring an archaeological site like Chirije, or exploring buoyant coastal metropolis Guayaquil. where you can find out more about Ecuador's chocolate-making legacy. It's prime time for visiting the Galapagos, when the comical blue-footed boobies begin their courtship and flamingoes breed and next. Waters remain warm and conducive for snorkeling and diving here.
Fiesta de la Chirimoya: May 3. This festival celebrates the delicious fruit better known in English as the custard apple, held on Isla Puná near Guayaquil. It's a good opportunity to try the local cuisine, themed around seafood.
Corpus Christi: Taking place in late May or early June, this is a religious festival and of course a good excuse for singing, dancing and eating traditional food. It happens in many locations across the Highlands, most notably Cuenca.