A study of high wind storms affecting Atlantic Canada, 1979--1995

A climatology of high wind events (HWEs) affecting Sable Island (44°N, 60°W) and Halifax (44.5°N, 63.5°W) was constructed for the period 1979--1995. We then focussed on HWEs at Sable Island in more detail because of their high frequency relative to Halifax. Events were stratified into four groups based on the direction of the peak speed: NE (1°--90°), SE (91°--180°), SW (181°--270°), and NW (271°--360°). Synoptic structures and statistically significant atmospheric anomalies were identified in composites for each group. More detailed structures were found in composites constructed with the aid of a cluster analysis.;NW HWEs were associated with rapidly deepening marine cyclones and lacked clear atmospheric predecessors. NE HWEs were linked to a slow moving offshore cyclone and prominent anticyclone near Labrador. An anomalously weak Icelandic Low was a dominant precursor signal and an important feature found in each of the groups. SE HWEs were related to the strong pressure gradient between a cyclone-anticyclone couplet. The anticyclone was evident four days before the HWE and played a crucial role in the development of the cyclone. SW HWEs were related to a variety of cyclone types, but were typically related to a low-frequency cold surge over eastern North America.;The storms most difficult to predict may be NW HWEs, since they lack clear atmospheric precursor signals. They are also among the most dangerous storms affecting Atlantic Canada, since they move and develop rapidly, and have some of the highest wind speeds.