"In 75 years of reliable data you only have one case where they were even 10 days apart," he said. And for Hawaii to be facing two spaced just two to three days apart? "This is unprecedented in the satellite era," Roth added.
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The National Hurricane Service said that after briefly slowing down, Iselle is expected to pick up speed and move faster towards Hawaii's islands on Tuesday and Wednesday. After forming as a tropical storm last week, Iselle picked up strength to gain hurricane status on Friday, and has built from there, according to The Weather Channel.
Iselle – now a Category 4 hurricane packing estimated winds of up to 140 mph – could weaken towards the end of the week, according to The Weather Channel, and hit Hawaii's islands as a large tropical storm. Swells are expected to start affecting coastlines on Wednesday and build from there, The Weather Channel reported.
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"The weather should start going downhill Thursday morning" for the Big Island, according to Roth. He said the worth weather for Honolulu and islands west will be Thursday night into Friday morning.
Tropical Storm Julio is "moving quickly west" and trailing behind Iselle, according to The National Hurricane Service.
Forecasters expect Julio to reach hurricane status as early as Tuesday and peak on Thursday, then most likely lost steam and get downgraded to a Tropical Storm before hitting the Big Island.
The eastern islands will get a brief respite Friday and Saturday, but forecasters warn that Tropical Storm Julio is then expected to start coming across late Saturday into Sunday.
—By Cassandra Vinograd, NBC News