North Pacific storm

47°06.2′N 146°22.7′W

Waves left about 20 Sep 07:08Z, ± 4 h

Placed by 2 buoys, whose own placements lie within 187 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