That is right. In Hawaii, we have had 24 Hour rainfall of 25 Inches with a Kona storm and this will cause serious flooding if the ground was soaked from prior storms (as happened in East Oahu in 1987). If we had a Hurricane or tropical storm trapped by a high pressure system, we could get rain-- 20-25 inches of rain or more over a few twenty four hour periods-- that kind of rain would overrun our drainage and ability of streets to carry water leading to undermining roadways and then becoming a "river" cutting streets into gullies and destroying homes. Homes in all the valleys and ridges are at risk of these fast flowing floods with enough rain. Street drainage and water just flowing over streets cannot handle flood water without destruction and flooding. Imagine water coming down Nuuanu (maybe busting the reservoir banks), Manoa, Palolo, Kalihi, St. Louis Heights, Mariner's ridge, etc. tearing up streets)