North Atlantic storm

23°34.7′N 042°33.7′W

Waves left about 27 Sep 02:25Z, ± 6 h

Placed by 2 buoys, whose own placements lie within 260 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