There's an easy way to get the behavior you want. Every 1 s, scan all parties, if their current target is not on the same continent as them (you'll can use some kind of voronoi diagram to check this - a simple way of explaining this is to say find the closest city and check what continent it's on, but that's not quite as precise as a well-drawn voronoi map), store their current goal in a buffer slot, and replace the current goal with travel to the nearest port.
http://en.wikipedia.org/wiki/Voronoi_diagram
For the port teleportation trigger, it's easy, every 1s, scan over all port cities, if there is a party close to the city with the goal "travel to next continent", then teleport it there, and restore the original goal that was stored in the buffer slot.
This way you don't even need to scan all the scripts to catch every possible invocation of goals. Parties can even follow other parties across the water with no problems... this includes bad guys chasing down the player.
