[Strategerist]

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.

[mewzilla]

Can these things be seen on radar? Not in time to turn the ship probably, but in time to tell folks to brace?

[rodguy911]

Typically the strongest currents in the Gulfstream are near the apex or center of the 50-60 mile wide north bound current. They can be 2-2.5 knots. Currents in the vicinity of 4-5 knots have been measured but are rare. They don't sound very strong but just try and swim against one.