Multiple

September 2023 featured three North Atlantic tropical cyclones (TCs) that had significant weather impacts at higher latitudes: Lee, Ophelia, and Nigel. These TCs were steered poleward and then eastward around a persistent anomalous high-latitude upper-level anticyclone that was situated over the northwestern Atlantic for much of September 2023. TC Lee caused widespread wind and flood damage as well as power outages in Maine and Atlantic Canada on 16–17 September. TC Lee weakened after landfall in Nova Scotia as it lost most of its tropical characteristics. It subsequently underwent a weak extratropical transition (ET), but it did not re-intensify explosively as an extratropical cyclone (EC). The extratropical remnants of TC Lee reached the UK on 19–20 September 2023 where high winds and flooding posed mostly minor problems. TC Ophelia made landfall as a mph tropical storm in Emerald Island, North Carolina on 23 September. The impacts of TC Ophelia were felt mostly in eastern North Carolina, Virginia, and the Delmarva Peninsula. The primary hazards associated with TC Ophelia were coastal flooding associated with a storm surge and inland flooding resulting from very heavy rainfall. TC Ophelia stalled to the east of the Outer Banks of North Carolina, redeveloped eastward initially as a non-intensifying EC (NHC declared Ophelia to be a post-tropical cyclone (PTC) at 0000 UTC 24 September). Once PTC Ophelia reached the east-central North Atlantic Ocean on 0000 UTC 26 September, it underwent ET and “bombogenesis” as an EC that was located near 47 N and 18 W at 0000 UTC 27 September. EC Ophelia brought very high winds, heavy rainfall, and flooding across parts of Ireland and Wales. TC Nigel was a central North Atlantic Ocean “fish storm” that moved poleward, recurved, and underwent ET. TC Nigel maintained hurricane status over the central Atlantic between 18–22 September. Widespread high winds and heavy rains occurred in the southern part of the UK as the remnants of former TC Nigel were ingested into a broad extratropical cyclonic circulation that was centered over the region.

The purpose of this presentation is to compare and contrast the structure and evolution of the aforementioned three TCs (Lee, Ophelia, and Nigel) that all subsequently reached higher latitudes along three different pathways and that all underwent different degrees of ET over the North Atlantic Ocean. TC Track data was obtained from the National Hurricane Center and Tomer Burg’s Realtime Tropical Cyclone website (http://arctic.som.ou.edu/tburg/products/archive/tropical/?basin=north_atlantic&year=2023). Alicia Bentley’s GFS historical map archive was used to help determine ET occurrence for the aforementioned three TCs. TC Lee was noteworthy for remarkably accurate TC track forecasts in the 5–10 day forecast time frame. As TC Lee approached Nova Scotia, a relatively short-lived inland coastal front formed adjacent to higher terrain over central Nova Scotia. This coastal front separated modified warm tropical air where the surface winds were southeasterly from cooler continental air where the surface winds were northeasterly. Although TC Ophelia was a weak TC, it taught us (once again) that we should never count out the ability of a slow-moving weak tropical system to cause trouble in the form of exceptionally heavy rainfall. As the weak remnants of TC Ophelia moved eastward across the Atlantic it gained its “second wind” as it interacted with a 70 m/s 250-hPa jet stream over the central North Atlantic. Former TC Ophelia underwent a strong ET over the east-central North Atlantic Ocean and reintensified to a sub-960-hPa bomb cyclone immediately to the west-southwest of the southern UK. The most rapid reintensification of former TC Ophelia occurred in the left jet-exit region of the aforementioned 250-hPa 70 m/s jet stream.

TC Nigel was situated over the central North Atlantic Ocean near 25 N and 50 W at 0000 UTC 18 September 2023. TC Nigel reached higher latitudes very quickly and by 22–23 September it underwent ET as it interacted with a potent upstream baroclinic trough situated near 50 N and 40 W. Eventually, the remnants of former TC Nigel were ingested into a broad baroclinic cyclonic circulation that also contained a sub-960-hPa cutoff cyclone situated over the northeastern North Atlantic Ocean. Ridging ahead of TC Lee resulted in enhanced downstream northerly flow aloft near 40 W that prevented a fourth TC (Margot; not discussed here) from moving NE toward Europe and interacting with a strong North Atlantic jet stream. A key takeaway from this active period of western North Atlantic TC activity was that an anomalous Central Atlantic upper-level anticyclone served as a conduit for poleward-moving TCs in the western Atlantic. Once these TCs reached higher latitudes they turned eastward and underwent varying degrees of ET. A broad quasi-stationary cold-core cutoff cyclone to the west of the UK served as an eventual "ring around the lowsie” graveyard for these former TCs that had previously experienced varying degrees of ET.