North Pacific storm

42°50.6′N 130°39.8′W

Waves left about 11 Sep 00:54Z, ± 2 h

Placed by 2 buoys, whose own placements lie within 118 nmi of it

Each buoy places the storm from how its swell's period shortened as it arrived: the longest waves travel fastest. Fronts are drawn at deep-water group speeds along great circles, and stop at land. How it is worked out