We can also view the +PV anomaly by animating a cross-section through its path. As the PV feature moves east, it intensifies; inducing offshore ascent.

Downstream cyclogenesis begins as ascent stretches frontal vorticity until occlusion.

Images adapted from @TropicalTidbits pic.twitter.com/mg1v3cKVAJ

— Philippe Papin (@pppapin) February 4, 2019