A Climatological Assessment of Greenland Blocking during Hurricane Sandy and Its Influence on North Atlantic Hurricane Tracks

In October 2012, an extreme area of high pressure centered near Greenland, known as a “Greenland block”, forced Hurricane Sandy to turn westward into the Northeast coast of the United States. In light of this unusual event and the recent increasing trend in the frequency of Greenland blocking patterns, the effects of Greenland blocking on North Atlantic hurricane tracks are examined from a climatological perspective. Spatially-averaged 500 hPa geopotential heights over the Greenland region were used to formulate a Greenland Blocking Index (GBI) to quantify the magnitude of Greenland blocking events. The GBI prior to Sandy's landfall on October 29 was found to be more typical of average conditions during late June, exceeding the 90th percentile of late October climatology during the entire week preceding the landfall and peaking at near-record values (99.8th percentile) on October 25. Above-normal GBI values were associated with a southward displacement of North Atlantic hurricane tracks and a greater concentration of hurricane tracks near the Northeast U.S. coast, but variations in Greenland blocking conditions were not associated with significant changes in the frequency of anomalous North Atlantic hurricane tracks (defined as tracks with an initial bearing angle of 90-360°). An atypical area of high pressure centered over the Canadian Maritimes was associated with anomalous hurricane tracks, while near-climatological conditions of tropospheric pressure across the North Atlantic prevailed for all normal hurricane tracks.