North Atlantic storm

51°57.1′N 018°11.9′W

Waves left about 20 Sep 23:45Z, ± 4 h

Placed by 4 buoys, whose own placements lie within 466 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