You will want a good warm rain coat with a hood.
Bring LOTS of garments.
Bring a hat to protect from the sun.
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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.