Found this online about the white squall (myth or not):

The white squall may be myth, or it may be a microburst. If they form during daylight you might see the approach as a line of broken water or whitecaps rushing at your vessel, but usually they appear out of nowhere.

"The Pride Of Baltimore, a fine 137 foot schooner, was reportedly struck by a white squall. The 121-ton vessel sank about 240 miles north of Puerto Rico, casting the surviving crew members adrift for five days. The Toro, a Norwegian freighter picked them up at 2:30 a.m. May 19th, 1986.

"Here is an eyewitness account of the sinking: ‘A tremendous whistling sound suddenly roared through the rigging and a wall of wind hit us in the back. The Pride heeled over in a matter of seconds. The 70-knot wind pushed a 20 foot high wall of water into the starboard side. She sank in minutes.’"

A USATODAY.com graphic shows what a microburst is. While the graphic shows what a microburst can do to an airplane that’s taking off or landing and much of the research into microbursts was prompted by the danger to aviation, microbursts have caused other kinds of damage on the ground and I know of at least one case in which a microburst overturned a boat, killing 11 people.

http://www.usatoday.com/weather/askjack/waoceans.htm

...interesting to read there about the "microbursts."

Also read several pro and con movie reviews of this film. Yeah, there are problems, but the shots of the ship in the sea are terrific.