Instead, Branson declared that he would hunker down with his team on his private, 74-acre Caribbean island - "as I have been on the three times we have had hurricanes over the past 30 years."
"On Necker Island we have constructed really strong buildings (with hurricane blinds) that should be able to handle extreme weather pretty well, though with a Category 5 hurricane almost nothing can withstand it," Branson wrote in a blog post, which also implied there would be no guests at his island's private resort when the hurricane hit. "We had some lovely guests staying on Necker Island who have cut their trip short for safety reasons, and another group of guests have also postponed."
Branson is the 324th wealthiest person in the world, with a net worth of about $5 billion, according to Forbes, which notes that he bought Necker Island for $180,000 nearly four decades ago.
On Wednesday night, before Irma hit, Branson said he and his team experienced "howling wind and rain."
He posted pictures of people smiling and bedded down in a room filled with furniture, backpacks and makeshift beds.
"All of us slept together in two rooms," Branson wrote. "I haven't had a sleepover quite like it since I was a kid. Strangely, it's a privilege to experience what is turning into possibly the strongest storm ever with such a great group of young people.
"We were listening to the parrots in their boxes in the next room chattering away. Watching the tortoises congregating together, as if they sense what is coming our way."
The National Hurricane Center had been calling Irma's conditions "life-threatening," noting that the ferocious, historic Category 5 hurricane could bring with it a devastating storm surge, destructive winds and dangerous flooding.
Despite the approaching storm, Branson said, people were "calm and upbeat."
A subsequent photo showed him seated with a group at a dining table, playing with dice.
A few hours before Irma's impact, Branson wrote that he planned to retreat with his team to his concrete wine cellar below "the Great House."
As one does.
"Knowing our wonderful team as I do, I suspect there will be little wine left in the cellar when we all emerge," he wrote on his blog.
And then, for hours: Silence.
No tweets, no Instagrams, no updates on Branson's blog - nothing.
The news from other islands in Irma's path was grim, with reports of widespread devastation and destruction.
Officials in France said at least eight people died in the French island territories of St. Martin and St. Barthelemy.
Barbuda, where Irma first made landfall, was left "barely habitable," according to government officials there.
Then, shortly before dawn Thursday, hours after Irma struck, Branson - or at least his Twitter account and blog - resurfaced with an update:
Everybody on Necker Island is safe - though the island itself "sustained extensive damage."
"We are deeply saddened by the events that have taken place in the last 24 hours and our hearts and thoughts are with our friends and family in the Caribbean," the blog post said. "We are very grateful to be able to report that all of our team on Island have been accounted for as safe as well.
"Necker Island felt the effects of Hurricane Irma and sustained extensive damage, the extent of which we are still assessing. We'd like to thank all of you for your thoughts and would like to assure you that we will be keeping you along, with our family and friends, updated this week as we know more. We will do whatever we can to support and assist our local community through this extremely testing time."
Glad to say that all humans on Necker are ok although a lot of buildings destroyed Very concerned for our friends and everyone on the neighbouring islands and people in its path. Please don't take this hurricane lightly if it is heading your way. If your building is not very solid, do find somewhere safe! Homes can be rebuilt but lives can't. Nature warning us again of the impact of #climatechange We must all do more to combat this. #nomoresubsidiesforfossilfuelandlivestockindustries #hurricaneirma #bvi #neckerisland #besafe #beprepared
On Instagram, the billionaire's son, Sam, noted the catastrophic strength of the storm - and pleaded with others in its path: "Please don't take this hurricane lightly if it is heading your way."
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