Though 2 houses washed away on the Big Island of Hawaii:

 They likely only lost one person in a Traffic Accident so far. So, mostly the Big Island has roads closed from Flooding and stuff like that so far. However, the rain is helpful in that most of the Hawaiian Islands have been in drought. The biggest problem is trying to hold onto the water for use of islanders I think at present. However, it is true many roads possibly have been undermined by the heavy rain too.

In fact, it might be places like Maui and Oahu and Kauai that might be actually hit harder than the Big Island of Hawaii as the population on the Big Island is more spread out but on Maui and Oahu and Kauai the population concentrations are greater in several places. So, if the population centers on the other Islands are hit with water beyond a certain point you might have flash flooding there too.

The point is that there is a lot of land on the Big Island for people to spread out and less land on all the other islands with larger population centers like Honolulu and the Kihei to Napili and Kapalua area of Maui with larger concentrations of people.

However, people also can be wise too about where they live and have watched previous storms in the past and so they have adapted pretty much to what can happen on the Hawaiian Islands too.