Is it still rainy season in October? The beauty is that the rain comes quick and fast for a short period of time in the afternoon. Wham, bam, thank you ma'am then it's over.
It's always steamy, so wear breathable fabrics and dress for heat. You don't need to go over the top with conservative wear but bring a light scarf to drape over your shoulders at temples if they'll be bare, plus one long skirt or pair of pants (linen rule) to cover your legs.