2B.5 Meteorological analysis of an extreme Beaufort coastal storm surge event

Monday, 1 June 2009: 11:30 AM
Grand Ballroom West (DoubleTree Hotel & EMC - Downtown, Omaha)
John R. Gyakum, McGill University, Montreal, QC, Canada; and D. Small and E. Atallah

The coastal community of Tuktoyaktuk on the Beaufort Coast of the Northwest Territories has experienced significant damage from storm surge events over the last several decades. The most dramatic impacts are observed during storm surge events that occur in the early fall (late July through early October) when the winter sea ice coverage has given way to large areas of open water. Scientific and anecdotal evidence both suggest that the storm surge event of September 1999 (S1999) was particularly damaging. Persistent high winds produced significant coastal erosion and saltwater intrusion that poisoned ground water supplies and killed trees and other vegetation in the Mckenzie River Delta. This study presents a detailed meteorological investigation of the atmospheric conditions that helped to produce such a devastating event.

The geometry of the coastline near Tuktoyaktuk is oriented such that only a northwesterly wind will produce the necessary fetch over open water favorable for storm surge events. A detailed climatology of the winds has confirmed that all of the known storm surge events at Tuktoyaktuk have taken place during periods of strong westerly to northwesterly winds. Previous studies have linked the high winds and storm surges in the region to the passage of cyclones along the Beaufort Coast. This study demonstrates that the S1999 event is a unique event with multiple stages and many different processes acting over a range of spatial and temporal scales.

Approximately one week before the storm surge began, a deep cyclone formed over the Gulf of Alaska and moved north over the coastal mountains towards the interior of Alaska. The subsequent weakening of the low and redevelopment to the north of the mountain range resulted in strong easterly winds along the Beaufort Coast. Strong easterlies are favorable for upwelling along the coast and were considered to be an important precursor for the generation of the storm surge and saltwater intrusion. A polar low then formed in the strong baroclinic zone that developed along the coast, producing strong northwesterly winds that eventually led to the actual storm surge. After the polar low moved ashore and decayed to the east of Tuktoyaktuk, a large cold air mass associated with an anticyclone to the north moved south and became trapped to the north of the coast Brooks Range. The cold air and rising geopotential height produced a pressure gradient and stratification favorable for northwesterly geostrophic winds aloft to be mixed to the surface. The implications for predictability of such a multi-faceted event are discussed.

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