In the morning the day is cool and you will need long clothes. As the day progresses and you begin to walk, you will have heat. I recommend detachable pants
It's humid and cold there on September, bring a jacket with you.
As others have said; it can be chilly given the higher altitude, proximity to the coast, and canopy cover blocking the sun, plus we've tripped into Autumn now. If you plan to walk around the longer/steeper paths, you'll likely want to remove a warmer layer but will be happy to have it elsewise.
Layers..can be very warm but could switch easily
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