Other contributing factor can be a strong current; Gulf Stream fits the bill, particularly if winds are against the current.
The most rogue waves in the world are between Madagascar and South Africa in the Agulhas current, which is even faster than the Gulf Stream.
A long history of killer crests
Rogue waves like the one that slammed into the Norwegian Dawn yesterday are more common and more dangerous than scientists first thought.
The waves, which can reach 15 to 80 feet high, have been responsible for the loss of more than 200 ships - including giant tankers and container vessels - in the past 20 years.
They also have caused damage to countless others, contradicting the long-held belief that only rare meteorological events could create the moving mountains of water. In fact, radar-based images last summer revealed 10 such waves in just a three-week period in the Atlantic Ocean.
In January, one such renegade wave smashed into the research vessel Explorer carrying nearly 1,000 people, including hundreds of students on a semester at sea program about 1,300 miles southwest of Anchorage in the Pacific Ocean.
The mammoth wave reared up in a voyage already wracked by storms, shattering windows on the 600-foot ship's bridge and shutting down three of its four engines.
Crews were forced to herd passengers into the center of the ship, which eventually limped into Hawai.
http://www.nydailynews.com/news/local/story/300795p-257522c.html
Thanks for the link. Lots of good information there.