Study on the influence of steering flows on the track of Hurricane Paulette (2020)

Hurricane Paulette (2020) underwent two critical track shifts over the North Atlantic: first, a turn from northwestward movement toward North America to northeastward movement, followed by extratropical transition; second, a shift from a northeastward track to a southward track, subsequently regenerating into a tropical storm. To investigate the influence of multi-level steering flows and surrounding circulation systems on these two turning processes, numerical simulations of Paulette were conducted using the Weather Research and Forecasting (WRF) model. The results show that: 1) The regeneration of Paulette was closely associated with its anomalous southward turning, during which it moved into a region of warm sea surface temperature, acquiring favorable conditions for redevelopment. 2) During the movement of Paulette, the steering flow exhibited significant vertical variation and evolution. The northwestward movement was primarily governed by low- to mid-level steering flows, while upper-level steering flows became more dominant during the northeastward turn and northeastward movement. During the southward-turning stage, low-level steering flows shifted from westerlies to northerlies, gradually extending upward to the upper levels and forming a deep northerly flow, ultimately leading to an abnormal southward turning of the hurricane's track. 3) In its early developmental stage, Paulette was located to the southern periphery of the subtropical high and moved northwestward under its blocking influence. As the hurricane intensified, the subtropical high weakened and broke, allowing Paulette to move northward into a mid-latitude westerly trough and turn northeastward under the influence of southwesterly flow ahead of the trough. However, as the high-pressure ridge to the south of Paulette continued to strengthen with a significant increase in meridional extent, the hurricane ultimately turned southward ahead of the ridge.