It is humid hot and humid cold. It does get pretty cold in the winter with the humidity. And it rains A LOT.
They walk so much in this mission. Send your missionary with some good tennis shoes along with their other shoes.
Get good boots that are waterproof. And really good quality socks. They wear through cheap socks and end up causing foot issues.
Also a waterproof bag.
Sisters are allowed to wear sandals in the summer. They walk through several pairs. Popular brands are Teva and Chacos.
Shoe dryers are pretty helpful.
Gold Bond medicated powder has been recommended for keeping bum, armpits and feet dry.
Sisters: Tampons are not always the best quality and can be quite expensive, so consider bringing a mission's supply or using a cup or disc.
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Most parents send their Elders with at least 1 suit (most countries in South America only wear suits to church and meetings) and around 8–10 golf pants. Families are sending more shirts because of heat and humidity — 12–14 is the average. Note for Sisters serving in Brazil: feminine hygiene products are expensive there and tampons are often considered taboo. Be prepared to send a good supply with your Sister Missionary.
Serve shirts have a ventilation panel in the side of the shirt making them noticeably more breathable. Missionaries serving in hot or humid places absolutely RAVE about this feature. The most popular shirt for hot-climate missions, for sure.