The damages from Hurricane Helene are still being calculated but the storm already ranks among the deadliest and costliest in US history.

With the number of Helene's victims reaching at least 100 on Monday, the powerful storm that swept the Southeast and triggered epic rainfall has become one of the deadliest hurricanes to make landfall on the U.S. mainland in the modern era.

Three storms over the past 13 months have hit South Carolina through the "back door." But researchers are unsure whether the trend will continue in the coming months.