I'd bring a rain jacket. We don't get many monsoons in Maryland but when we DO get them, it's in September. Lots of spin-off storms from the Atlantic coast hurricanes--they hit the fall line and stop, dumping a steady rain all day or numerous small storms throughout the day.

+1 on the bug spray. You may not even need it particularly on the bike when you're moving and they aren't so active, but in the evening when you're just hanging around and they are flying around looking for something to devour, you'll be glad of it.

Sarah