Hurricane Iselle was drawing a bead on the Big Island of Hawaii Thursday morning. By the afternoon the first squalls of tropical storm force will reach the east side of the island.
Hurricane force winds are expected later Thursday evening as the center moves onto the island. If hurricane force winds are measured on the Big Island, this will be the first time in recorded history for the island to experience a hurricane.
The Big Island has the tallest mountains in Hawaii, topped by Mauna Loa which is over 13,000 feet. Wind speeds on the north and east facing slopes will be higher than the wind at sea level. Moreover, the upslope winds will lead to extremely torrential rainfall as Iselle moves through.
On the plus side, Iselle is moving rather quickly at 18 mph, which means the strongest winds and rains won't last as long as a slower-moving storm. Also, the mountains should take a toll on Iselle, reducing the winds below hurricane strength and possibly lessening the impact on the rest of Hawaii.
On the Big Island, I expect we will see some significant flash flooding and mud slides from late Thursday into Friday. The strong winds will produce power outages and some property damage. Huge waves will be crashing ashore on the eastern coast of the island.
Iselle is forecast to move through all of the Hawaii bringing heavy rain and tropical storm force winds before moving west of the islands on Saturday. Impacts from Iselle to the rest of the islands depends on how much Iselle is diminished after moving over the Big Island. Significant winds and rains will still be possible with local power outages and flash flooding being the main threats.
Hurricane Julio is about three days behind Iselle and heading in the general direction of Hawaii. However, Julio is currently forecast to pass just to the north of the Islands, which would be a relief as impacts would be considerable less severe.
In the Atlantic Ocean, all is quiet Thursday.