North Atlantic storm

46°57.2′N 018°39.7′W

Waves left about 21 Sep 11:13Z, ± 3 h

Placed by 3 buoys, whose own placements lie within 354 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