becuse models are global they have to be. Bye telling the winds winds over say the indain ocean where no recon can get to you can get an idea of the pressure in the area ect and what the pressure over the indian ocean or south pacific or north pacific even the northern atlantic will all have an effect on each other. If you cant see whats going on 5000 miles out in the middle of the pacific then the model cant see it and what it thinks will be wrong. The world is a slip stream genrally what is going on over japan will effect what is 3 days off the coast of america.