Extreme Atlantic Swell Event of March 2008

(A higher resolution image is available by selecting the image of interest.)

Synopsis
On the night of Saturday, March 15, 2008, a strong short wave trough and accompanying surface low moved quickly off of the mid-Atlantic coast of the U.S. This deep layered feature slowed its forward motion and deepened to 984 mb, as it moved east northeastward into the northwest Atlantic by 00Z, March 17, 2008.

Figure 1: Satellite imagery of a large surface low deepening off the northeast coast of the United States taken on March 17, 2008 at 0000Z.

This large surface low then deepened rapidly during the next 24 hours, to 964 mb by 00Z on the 18th, and then drifted northeast through the 20th, before eventually weakening significantly and shifting southeastward across the central Atlantic. The nearly stalled nature of the synoptic feature allowed for a very strong and broad north to northwest wind fetch to spread from the Canadian Maritimes and the northeastern U.S. coastline south and southeastward across the west central Atlantic, to nearly 25 degrees north.

Figure 2: Satellite-derived winds from QuikScat imagery reveal extremely strong counterclockwise flow around the center of the deepening low pressure system. The deep purple wind barbs across the center of the image reveal winds in excess of 50 knots (nearly 60 mph).

A strong and dynamic wind fetch associated with this expanding wind field produced extreme wave growth, and spread large and very long period swells propagating across the entire regional Atlantic, to the Bahamas, across the Greater and Lesser Antilles, to the northeast coast of South America, and across the entire tropical Atlantic, continuing to the west African coast and into the south Atlantic. Locally across Puerto Rico and the U.S. Virgin Islands, extreme breaking wave heights of 20 to 30 feet were common from early on the 19th through the 21st, with occasional breaking waves reaching 35 to 40 feet and higher across the outer reef lines.

Figure 3: Waves crashing across an outer reef along the north coast of Puerto Rico.

Figure 4: An impressive breaking wave near the outer reef along the northwestern coast of Puerto Rico.

These swells rivaled the swell event produced by the “Perfect Storm” of October 1991, which killed two teens on the island in its aftermath. Recent regional wave history suggests that this size and wave length has a return period of 15 to 20 years.

Figure 5: Newspaper article on the aftermath of the coastal flooding event of October 1991.

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