Hurricane Fiona strengthened into a Category 3 storm on Tuesday morning — packing 115 mph winds as it neared the Turks and Caicos Islands.

Threat level: The deadly storm that's the first major hurricane of the 2022 Atlantic hurricane season was continuing to unleash heavy rainfall and "life-threatening" flash flooding on Puerto Rico and parts of the Dominican Republic, per a National Hurricane Center 2am update.

2am AST 20 Sep -- Air Force Reserve Hurricane Hunter (@53rdWRS) data indicates that #Fiona has become a Category 3 hurricane. Fiona is the 1st Major Hurricane of the 2022 Atlantic Hurricane Season.

Maximum sustained winds are up to 115 mph.

Latest: https://t.co/EG1Nt92Czm pic.twitter.com/GCk9dyiE7d

— National Hurricane Center (@NHC_Atlantic) September 20, 2022

• The hurricane has been linked to at least two deaths in Puerto Rico and another one in the nearby Dominican Republic.

The big picture: Fiona caused a total power outage when it struck Puerto Rico as a Category 1 storm over the weekend. Nearly 1.3 million residents were still without electricity in the U.S. territory on Tuesday morning, according to poweroutage.us.

• After it made landfall in the Dominican Republic on Monday, the strengthening storm knocked out power to more than 700,000 customers, Reuters notes.
• The White House said Monday the federal government has deployed 300 personnel to Puerto Rico to assist with response and recovery, and this would "increase substantially" in the coming days once the damage has been assessed.

Of note: Puerto Rico's power grid was already fragile after being severely damaged during Hurricane Maria in 2017.

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Editor's note: This article has been updated with new details throughout.