North Pacific storm

30°32.4′N 142°53.8′W

Waves left about 28 Sep 01:12Z, ± 5 h

Placed by 2 buoys, whose own placements lie within 108 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