Multiple Tropical Cyclone-Baroclinic Trough Interactions over the North Atlantic Ocean during September 2023

North Atlantic (NATL) Tropical Cyclones (TCs) Lee, Nigel, and Ophelia in September 2023 were all associated with significant weather impacts. This presentation will compare and contrast differing extratropical transition (ET) pathways followed by these three TCs. Data was derived from the National Hurricane Center, Tomer Burg’s Realtime TC website, Alicia Bentley’s GFS historical map archive, and ERA-5 gridded analyses.

TC Lee brought heavy rain to Nova Scotia, weakened after landfall, became associated with an inland coastal front, underwent ET, and caused heavy rain and flooding the UK on 19–20 September 2023. TC Nigel produced widespread high winds and heavy rains over parts of the UK as its remnants were ingested into a broad extratropical cyclonic circulation. TC Ophelia moved poleward along the US East Coast, weakened into a post-tropical cyclone (PTC) over eastern Virginia where it stalled. PTC Ophelia was associated with exceptionally heavy rains from eastern Virginia to New England. Rainfall, especially heavy along a coastal front that formed poleward of PTC Ophelia, extended into the New York City area where severe flooding occurred.

A weak warm front that extended southeastward over the Gulf Stream from PTC Ophelia over eastern Virginia spawned two extratropical cyclones, one of which brought hurricane force winds, heavy rains, and flooding to the UK where it was renamed “Storm Agnes”. We will focus on how the interactions of TCs Lee, Nigel, and Ophelia with individual baroclinic upper-level troughs resulted in multiple “flavors” of ET over the NATL Ocean, and how baroclinic cyclogenesis along a weak warm front that extended southeastward from PTC Ophelia ultimately upscaled into a bomb cyclone (Strom Agnes) that created meteorological havoc across the UK.