Extreme Atlantic Swell Event of March 2008


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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

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

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

Figure 4

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

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

 Synoptic Evolution
A very fast and progressive mid to upper tropospheric pattern prevailed across the mid latitudes of the U.S. on Thursday, Friday, and Saturday, March 13th, 14th, and 15th. Two strong and energetic short wave troughs moved quickly across the central and then southeastern states during this weekend and interacted with moist unstable atmospheric conditions to produce severe weather. The first of these two short waves moved across the southeastern states Friday evening, accompanied by a broad surface low, and then turned northeastward across the northwest Atlantic, where it quickly deepened to a 990 mb low. The mid latitude upper level flow across the Atlantic immediately prior to this time was depicted by a relatively low amplitude two wave, very progressive pattern, as a positive NAO pattern had dominated the Atlantic for most of the winter season . However, as the second of these two short waves moved into the western Atlantic, the upper flow transitioned to a broad omega blocking pattern across the entire north Atlantic, and effected a brief negative phase of the NAO.

Figure 6
Figure 6: Animated loop of 500 mb heights revealing an omega blocking pattern in the North Atlantic.

The second of these short waves exited the Outer Banks of North Carolina overnight Saturday the 15th, accompanied by a 998 mb surface low and moved east northeastward, directly over the Gulfstream’s warm waters, and continued to deepen through Sunday morning.

Figure 7

Figure 7: Sea surface temperatures showing the Gulf Stream influences in the Atlantic Ocean.

During this time, this deep layered and intensifying low evolved into the western low of a North Atlantic omega blocking pattern. This allowed for explosive deepening of the low Sunday afternoon through Monday evening as it became cut off from the main flow and moved more slowly northeastward, continuing directly over the Gulfstream. By 00Z on Tuesday the 18th this low was analyzed at 964 mb near 41 North 55.5 West.

Figure 8

Figure 8: Animated loop of surface analysis charts depicting the deep low pressure system in the Atlantic.

A broad zone of cold Arctic air was in place from the Great Lakes region north and eastward across North America prior to the passage of the two short waves. This cold polar air, supported by a 1038 mb high over eastern Canada, advected south and southeastward behind the deepening low and contributed to a broad zone of very strong surface winds that exited the northeastern U.S. and spread quickly south southeastward across the northwest and western Atlantic. This also forced a cold front to sweep off the eastern seaboard, across the West Atlantic, through Florida and into the Bahamas. The deep low pressure center then drifted very slowly northeastward over the next 36 hours between 58 and 54 West, while curving cyclonically within the larger deep layered cyclonic circulation. The very slow motion of this low during the period from Monday morning through Tuesday evening, supported by the strong and dense polar air spilling into the northwest Atlantic on its backside, produced a broad zone of 35-50 kt winds that spread from the Canadian Maritimes and coastal New England, south southeastward into the west central Atlantic to 30 North. Within this large wind field, and near the center of the low, remotely sensed wind observations revealed that a narrow zone of hurricane force winds rotated through the western semicircle.

Figure 9

Figure 9: Satellite-derived winds from QuikScat imagery reveal strong counterclockwise rotation around the deepening low pressure system.

The high pressure ridge to the west and northwest of the low shifted slowly east and northeastward in tandem with the low during its passage across the Atlantic to maintain a very tight pressure gradient across the western semicircle of the low. This pressure pattern configuration allowed for a broad and dynamic fetch to set up from the Canadian Maritimes and coastal New England, spreading south and southeastward across the western Atlantic to near 25 North by Wednesday the 19th.

Swell Generation and Propagation
Large northerly swells were being generated across the west and northwest Atlantic on Sunday the 16th, under the influence of the strengthening winds in the northwest and western portions of the deepening low, and behind its associated cold front sweeping through Florida and into the Bahamas. As this low began to deepen explosively late Sunday through Monday the 17th, the very tight pressure gradient and cold dense air across the Canadian Maritimes and New England induced a very large area of 40 to 65 kt winds 450 to 720 nm wide that spread south and southeastward to near Bermuda.

Large northerly swells generated across the northwest Atlantic during the preceding 24 hours were given further opportunity to grow as this very large wind fetch spread south and southeastward through Monday. This broad wind fetch generally persisted in strength and size while shifting slightly eastward through 21Z on Tuesday the 18th. Extreme wave growth had occurred during this time period, as northerly swell, generated across the northwest Atlantic Sunday through Monday, moved with and directly underneath the broad wind field expanding south and southeastward behind the cold front. By Monday morning, tremendous waves of 30 to 40 feet had grown across the northwest Atlantic, in the west and southwest quadrants of the low, while just a bit further to the west, longer period northerly swells near 20 feet were propagating southward and had begun to reach Bermuda.

Figure 10

Figure 10: Animated sea-state analysis loop depicting high seas propagating from the center of the low.

By 12Z on Tuesday, the cold front had reached the north coast of Puerto Rico, accompanied by the first pulse of long period north swells. Buoy 41043 located north of St Thomas, had observed these north swells of 7.5 ft at 12 seconds just a few hours earlier. Swells grew slowly but steadily throughout the day on Tuesday reaching 10 feet at the buoy by noon. A next pulse of swell was registered at the buoy at 21Z late that afternoon, at 13 seconds. Swells built more rapidly during the next few hours at the buoy, reaching 14 feet by 02Z on Wednesday the 19th. This would turn out to be the leading edge of 72 hours of very large, very long period, and extremely powerful northerly swells that would pound the local Atlantic coastlines with huge surf and extensive coastal flooding.

Figure 11

Figure 11: Graph of significant wave heights during the progression of the event at buoy number 41043 located north of Puerto Rico.

Figure 12

Figure 12: Graph of swell periods during the progression of the event at buoy number 41043 located north of Puerto Rico.

Observations taken from buoy 41043, and from an AWOC deployed on the northern shelf waters of the Virgin Islands by the University of the Virgin Islands showed two pulses of swell at 16 to 17 seconds and 14 to 16 feet between 12Z on Wednesday the 19th and 06Z Friday the 21st, which was the peak of this rare event. These wave lengths allowed these swells to reach the local Atlantic coastlines within 3 to 5 hours of hitting these sensors. Gigantic walls of whitewater covered the horizons during this time as frequent breaking waves of 20 to 25 feet prevailed along the outer reefs and shoals of the local islands, with infrequent waves of 30 to 40 feet. A handful of extreme surfers were photographed surfing mountainous waves of 30 to 40 feet on Wednesday at Puerto Rico’s world renowned big wave spot, Tres Palmas, located on the west coast in Rincon.

Figure 13

Figure 13: Picture taken during the height of the event along Puerto Rico’s Tres Palmas, in Rincon, on the west coast of Puerto Rico.

Figure 14

Figure 14: Picture taken during the height of the event along Puerto Rico’s Tres Palmas, in Rincon, on the west coast of Puerto Rico.

Swells registered at these two sensor sites began to fall below 12 feet after 12Z on the 21st, and then gradually diminished below 8 feet by 03Z on Saturday the 22nd. Meanwhile, across the rest of the Atlantic, this same swell energy had moved through the Atlantic passages and into the Caribbean, reaching the north coast of Venezuela Wednesday afternoon. These very long period swells also propagated southward along the Lesser Antilles island chain, and into the tropical Atlantic, and continued south and southeastward across the rest of the tropical and south Atlantic. Based on the analyzed wind field from remote sensing and available ship reports, the strongest and largest swell energy with this event was directed towards the tropical Atlantic east of the Lesser Antilles, and would have struck the coastlines of Guyana, Suriname, French Guiana, and the entire northern coast of Brazil.

 Impacts across Puerto Rico and the U.S. Virgin Islands

As a result of the storm’s impact, major beach erosion, as well as significant damage to coastal roads and homes, was reported along the shore. Some of these coastal roads were closed for several days. Specifically, debris and sand deposits were reported along Road 681 from the municipality of Barceloneta to Arecibo.

In the Vega Alta municipality, the Balandra sector in Cerro Gordo was closed. In the Vega Baja municipality, Road 686 was closed near the Puerto Nuevo beach. In the Arecibo municipality, the seafront Victor Rosa Avenue was closed. The same road also suffered significant damage and erosion. The high surf also eroded the fence surrounding the Arecibo lighthouse.

Figure 15

Figure 15: Picture taken along the coastline in Arecibo during the height of the swell event.

The surf reached the sea wall at Ocean Park, in San Juan. In addition, Road 187 at Piñones was closed to traffic from the Cangrejos Bridge to Vacia Talega Sector. Several homes were affected by the swells in Piñones and Colobo, such that eleven families were relocated. In the municipality of Luquillo, at Playa Fortuna, some properties suffered damage when the high surf broke into a coastal vacation home at Sector Villa Falcon. At La Pared sector the surf washed on the road.

Figure 16

Figure 16: Picture taken along the bike path in Piñones showing the destruction the waves caused.

The surf encroached on the parking lot at Punta Maracayo in the municipality of Hatillo. Punta Maracayo camping ground was evacuated, 80 persons were relocated to the hotel. Road 485 in Camuy was closed. Road 119 from Hatillo to Camuy was closed. In Isabela, Road 466 at Playa de Jobos was closed.

In addition, the San Juan Bay was closed to marine traffic for several days and the ferry service from Fajardo to Vieques and Culebra was suspended for several days.

The storm brought a large amount of visitors to the beach trying to view the large waves. Law enforcement, emergency managers, and public works personnel monitored coastal areas and alerted surfers and visitors to remain out of the water. The Puerto Rico Tourism Department alerted all hotels before the onset of the large swells. Additionally, public beaches along the northwest, north, and northeast were closed for several days.

Figure 17

Figure 17: Picture taken along the north coast depicting coastal flooding while spectators watched the impressive surf strike the shore.

Figure 18

Figure 18: Picture taken at Vega Baja depicting the dangerous surf conditions crashing ashore at the height of the event.

Figure 19

Figure 19: Picture depicting the “spectator sport” at Vega Baja that was a direct result of the impressive waves.

Figure 20

Figure 20: Picture depicting some of the damage the occurred as a direct result of the high surf and coastal flooding in Loiza.

 


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