Tropical cyclones often weaken as they approach Hawaii due to cooler water temperatures, drier and more stable air, and an increase in wind shear (the change in wind speed and/or direction with height). This makes strong hurricanes close to Hawaii an unusual occurrence.
From 1950 to 2017, only 14 hurricanes have passed within 200 nautical miles of the Big Island, Maui, Honolulu or Kaui, according to NOAA's historical hurricane database. The most recent one to do so was Hurricane Ana in October 2014.
Abundant moisture will spread through the islands from east to west through Friday.
Rainfall totals of 10 to 15 inches are anticipated. Isolated areas could see more than 20 inches of rainfall, especially where rainfall will be enhanced by upslope winds on southeastern and eastern facing mountain slopes.
Flash flooding and mudslides are likely and the National Weather Service has indicated that there is the potential for extreme flooding rain across the Hawaiian Islands.