North Pacific storm

30°42.7′N 135°55.7′E

Waves left about 20 Sep 14:53Z, ± 8 h

Placed by 2 buoys, whose own placements lie within 186 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