It is officially hurricane season in Hawaii. Pacific hurricane season is May 15th to November 30th. Iniki hit Kauai on Sept 11th, late 1990's, I can't remember the exact year. It was a devasting hurrican.
Although the likelyhood of the islands being impacted is low.
The running joke about weather in Hawaii is that the different between night and day is greater than the difference between summer and winter. So basically night is winter in Hawaii.
On the big island the main highway from Waikaloa to the Airport is closed during the ironman, as that is the road the cyclist use. There is a back road that is not so direct, but you can make it back to the airport on. It just takes more time.
You should look up your schedule and the races scheduled times. There should be something posted.