The WWIII REGIONAL WESTERN NORTH ATLANTIC(WNA) data covers the US east coast, Gulf of Mexico, Caribbean, and Central America from latitude 50 north to the equator and out to 30 west. It is .25 X .25 resolution meaning the points increment by .25 degrees. No coverage over land and valid points are usually 15NM offshore.

You can use a GPS or just estimate your lat/long position by using the weather charts. For this model, all longitude inputs are negative. No letters like N, W, E, or S go in the inputs. 90 degrees west is entered as -90.