Impacts of Extratropical Wave Breaking on Atlantic Tropical Cyclone Activity
Further examination suggests the active anti-cyclonic Rossby wave breaking and frequent equatorward intrusions of extratropical air in August 2013 were associated with changes of the midlatitude jet stream (i.e., acceleration, eastward extension and greater strain rate). The EOF analysis of 200-hPa zonal wind identifies a recurrent mode of interannual variability over Atlantic. This mode is associated with the variations of the intensity and zonal extent of the mid-latitude jet and is found significantly correlated to Atlantic hurricane frequency in August. Our analyses thus emphasize the extratropical impacts on Atlantic tropical cyclones via the Rossby wave breaking. This physical link is missing in most statistical forecast schemes and may help explain the seasonal prediction bust in 2013.