Anticosti Vortices

In eastern Canada, the large island of Anticosti lies between the mouth of the St. Lawrence River and the main part of St. Lawrence Bay. In both visible and infrared satellite imagery today, two mesoscale cyclonic vortices have been remarkably persistent approximately south of the eastern and western tips of Anticosti Island.

The high-resolution MODIS satellite data provides a beautiful close-up view of the vortices.

The surface analysis from NOAA NCEP Hydrological Prediction Center shows generally weak easterly flow over the region, ahead of a weak warm front.

Looking at the nearby radiosonde sounding from Sept-Iles reveals an inversion layer with northeasterly flow below about 950 hPa (600 m), with shear to northwesterly flow above. Although the highest elevation on Anticosti is around 300 m, it is likely that the island itself is largely responsible for deflecting the flow sufficiently to form these nearly stationary vortices.