Endurance swimmer Penny Palfrey pushed through the calm waters of the Florida Straits overnight and through the Saturday dawn, enduring jellyfish stings but otherwise encountering perfect conditions as she neared the halfway mark in her attempt to become the first woman to swim unassisted from Cuba to Florida.

By 8:38 a.m. EDT (1248 GMT), a little over 25 hours into the swim, the 49-year-old grandmother was 48 miles from her starting point at a marina in the Cuban capital, Scott Woodburn, who is part of Palfrey's landing team in the Florida Keys, told The Associated Press.

Woodburn said Palfrey was smiling and barking orders at team members accompanying her on kayaks and a catamaran as she kept up a torrid pace in a battle that tested the limits of human endurance and the will of the high seas.

She is "alert and swimming physically strong," Woodburn said, adding that the bathwater-warm waters remained calm. "It couldn't be better for her."