North Pacific storm

38°52.0′N 140°30.5′W

Waves left about 25 Sep 20:42Z, ± 2 h

Placed by 2 buoys, whose own placements lie within 489 km 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