North Pacific storm

42°10.4′N 153°35.2′E

Waves left about 23 Sep 08:34Z, ± 7 h

Placed by 3 buoys, whose own placements lie within 150 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