By Dan Bikos and Sheldon Kusselson
Hurricane Fiona underwent a transition from a tropical cyclone to an extra-tropical cyclone on 23-24 September 2022. The ensuing extra-tropical cyclone was very intense and led to important storm surge, wind harm and heavy rain in southeast Canada centered on Nova Scotia.
The Advected Layer Precipitable Water loop does a superb job of capturing the transition to an extra-tropical cyclone. The decrease left panel shows the precipitable water within the 700-500 mb layer. Notice the dry air mass that’s initially southwest of the floor low, wrap cyclonically across the low. This dry air intrusion at mid-levels is attribute of extra-tropical cyclogenesis because the dry conveyor belt (additionally known as dry slot) develops and intensifies. The ALPW loop additionally reveals the plentiful low-level moisture transported northward forward of the floor low in the direction of Nova Scotia, contributing to the heavy rain occasion.
For an additional perspective of the extra-tropical cyclogenesis occasion, we flip to the three water vapor bands together with the air mass RGB product. The hotter brightness temperatures noticed within the water vapor bands are initially southwest of the floor low and wrap cyclonically across the low. That is coincident with the dry air intrusion with the dry air within the ALPW 700-500 mb layer since this can be a subsidence signature.
One of many options we see within the water vapor imagery are these a number of traces indicated by the yellow oval proven beneath:
This can be a sting jet at low-levels and is usually noticed with very sturdy winds on the floor.
Extra info on sting jets