Nyad, 64, is on her fifth attempt to swim the 103 miles from Cuba to Florida without a cage, wet suit or flippers.

At 3:54 a.m., her support team tweeted, "10-mile countdown is ON!" Nyad had never before come so close to Florida in previous attempts, and on Sunday night she broke Penny Palfrey's record for the farthest anyone has managed on the trek without a shark cage.

In 1997, Australian Susie Maroney completed the swim from within a shark cage. She was 22 at the time.

Nyad's website reported the leaders of her five-boat support team were planning her final route into Key West, taking into account tides, currents, shipping lanes, reefs and "swarms of jellyfish."

Nyad, who began the swim from Cuba on Saturday morning, may be in position to reach land between 4 p.m. and 6 p.m. ET, the website said Monday morning.

"Diana has stopped numerous times to tread water trying to restore herself," Nyad's navigator, John Bartlett, said in a website post at 5 a.m., 44 hours into the swim. "We don't know how strong she is swimming at this point, but we'll get an update soon."

Nyad is using a special mask to prevent jellyfish stings to her tongue -- a key factor in her failed attempt in August 2012.

Thunderstorms also helped thwart her last year.

The weather this weekend was much better until 11 p.m. Sunday, when the support team reported winds rose suddenly and a thunderstorm appeared headed toward Nyad's path.

But just before 1 a.m. Monday, the team reported on Twitter: "Diana is swimming strong, everyone is safe, the winds are dying down, and we think we see the glow of Key West!"

Bartlett wrote on her website earlier that a favorable Gulf Stream had helped her achieve an average speed of 2.2 miles per hour.

Bartlett said currents will be "smaller but less predictable" as Nyad nears Florida.

Handler Bonnie Stoll wrote on the site Sunday that Nyad was in good spirits.

"The only concern is that she is throwing up everything she eats. She's quite nauseous from sea salt, but that's to be expected," said Stoll. "We're giving her enough calories and nutrition. We're just going to keep feeding her, and we hope that some of it is going down. She's not weak. Her stroke count hasn't changed."

Nyad set out from Havana at 8:59 a.m. Saturday with a crew of 35, including divers to watch for sharks.

The Los Angeles woman has said this is her final attempt. She said on her website that she wants to prove "it's never too late to chase your dream."