Nyad, who turns 63 on Wednesday, is making her third attempt since last summer to become the first person to swim from Cuba to Florida without a shark cage. She also made a failed try with a cage in 1978.
"She's doing well," a spokeswoman for the swimmer, Alex Crotin, said Monday afternoon.
Nyad had been expected to arrive somewhere in the Florida Keys early Tuesday, but her team tweeted Monday evening that she "lost six hours progress" in overnight storms Sunday. The team tweeted that a storm had blown Nyad off course and that "all hell broke loose" in the squall.
Monday offered far more ideal conditions, with blue skies and level seas and the Gulf Stream offering beneficial currents.
Nyad's team said the swimmer's spirits were lifted Monday afternoon by a surprise visit from a boatload of friends and family. And Monday evening, she found herself swimming among dolphins, a far happier scenario than the sharks that were feared.
"The skies are clear, the sun high in the sky," crew member Brandon Beach wrote on Nyad's blog, calling it "a pretty gorgeous day out here in the middle of the ocean."
Still, the swimmer's crew was improvising ways to prevent hypothermia and to fend off further swelling of her lips and tongue. Though she's swimming in 85-degree waters, because that is lower than the body's core temperature, it will reduce her body temperature over time. Her team said she had been shivering.
"We all know her mind can handle it," Candace Hogan, a crew member travelling with Nyad, wrote on the swimmer's blog. "But there will always be a point where a human body can't go any farther. What no one knows is where that line is drawn in Diana Nyad."
Based on her progress — she logged her 60th mile after midnight Tuesday, with more than 40 miles left to go — she would likely arrive significantly after her low-end estimate of 60 hours after starting.
Australian Susie Maroney successfully swam the Straits in 1997, but she used a cage. In June, another Australian, Penny Palfrey, made it 79 miles (127 kilometres) toward Florida without a cage before strong currents forced her to abandon the attempt.
Nyad has already endured jellyfish stings on the current attempt. Stings forced her to cut short her second of two attempts last year as toxins built up in her system.
Nyad has been training for three years for the feat. She is accompanied by a support team in boats, and a kayak-borne apparatus shadowing Nyad helps keep sharks at bay by generating a faint electric field that is not noticeable to humans. A team of handlers is always on alert to dive in and distract any sharks that make it through.
She takes periodic short breaks to rest, hydrate and eat high-energy foods such as peanut butter.
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