Tropical Transition of an Unnamed, High-Latitude, Tropical Cyclone over the Eastern North Pacific

Abstract

In early November 2006, an unnamed tropical cyclone (TC) formed via the tropical transition (TT) process at 42°N over the eastern North Pacific. An extratropical cyclone (EC), developing downstream of a thinning upper-tropospheric trough over the eastern North Pacific, served as the precursor disturbance that would ultimately undergo TT. The TT of the unnamed TC was extremely unusual—occurring over ~16°C sea surface temperatures in a portion of the eastern North Pacific basin historically devoid of TC activity. This paper 1) identifies the upper- and lower-tropospheric features linked to the formation of the EC that transitions into the unnamed TC, 2) provides a synoptic overview of the features and processes associated with the unnamed TC’s TT, and 3) discusses the landfall of the weakening cyclone along the west coast of North America. As observed in previous studies of TT, the precursor EC progresses through the life cycle of a marine extratropical frontal cyclone, developing a bent-back warm front on its northern and western sides and undergoing a warm seclusion process. Backward air parcel trajectories suggest that air parcels isolated in the center of the transitioning cyclone were warmed in the lower troposphere via sensible heating from the underlying sea surface. Vertical cross sections taken through the center of the cyclone during its life cycle reveal its transformation from an asymmetric, cold-core, EC into an axisymmetric, warm-core, TC during TT. Ensemble reforecasts initialized after TT highlight the relatively low forecast skill associated with the landfall of the weakening cyclone.

Subtropical cyclones over the oceanic basins: a review

“…The PV framework includes contributions from: (1) low‐level baroclinic processes, (2) convective latent heat release in the mid‐troposphere, (3) upper level cold cutoff lows or troughs, and (4) dynamic changes in the upper troposphere. In the period 1979–2010, there were a total of 62 cases of hurricanes originating from the tropical transitions of subtropical storms . The preferred genesis location is over the western North Atlantic basin, with fewer cases occurring over the Gulf of Mexico and over the eastern sector of the basin.…”

“…The tropical transition mechanism described shows the transformation of an existing cold core cyclone into a hurricane, but it can also explain the tropical transition of a pure subtropical cyclone into a deep warm core tropical cyclone. Bentley and Metz presented a climatology of such transitions over the North Atlantic basin using a PV framework instead of CPS to identify subtropical cyclones. The PV framework includes contributions from: (1) low‐level baroclinic processes, (2) convective latent heat release in the mid‐troposphere, (3) upper level cold cutoff lows or troughs, and (4) dynamic changes in the upper troposphere.…”

“…The three parameters of CPS are extremely useful to distinguish extratropical and tropical cyclones, different types of extratropical cyclones, tropical and extratropical transitions, and to characterize subtropical cyclones . Time evolutions through the storm lifecycle of B , – V T L , and – V T U are clearer in the phase diagram proposed by Hart.…”

The Tropical Transition in the Western North Pacific: The Case of Tropical Cyclone Peipah (2007)

“…Alternatively, the colder and drier air transported into the upper troposphere serves to destabilize the tropospheric column by enhancing convective available potential energy (CAPE), thus to foster convectively favorable environments (Juckes & Smith, 2000). The associated anticyclonic wave breaking (and PV streamer) over the tropical eastern Pacific and North Atlantic has been attributed to the formation of subtropical cyclones, which can subsequently undergo tropical transition (Bentley et al, 2017;Bentley & Metz, 2016;Davis & Bosart, 2003Galarneau et al, 2015).…”

Multiscale Upstream and In Situ Precursors to the Elevated Mixed Layer and High-Impact Weather over the Midwest United States

“…Archambault et al (2013) illustrate that interactions among recurving and extratropical transitioning western North Pacific tropical cyclones (TCs) and the North Pacific jet stream are a critical process in large-scale flow reconfigurations that produce Rossby wave train (RWT) amplification and dispersion via downstream development (e.g., Harr and Elsberry 2000;Klein et al 2002;Atallah and Bosart 2003;McTaggart-Cowan et al 2007;Riemer et al 2008;Harr and Dea 2009;Riemer and Jones 2010;Archambault et al 2015;Torn and Hakim 2015;Quinting and Jones 2016;Grams and Archambault 2016). Both TC-influenced and non-TCinfluenced RWTs can disperse downstream along the North Pacific waveguide and can influence the evolution of the flow over the North Pacific and North America (e.g., Chang 1993;Orlanski and Chang 1993;Orlanski and Sheldon 1995;Danielson et al 2004Danielson et al , 2006Cordeira and Bosart 2010;Archambault et al 2015;Torn and Hakim 2015;Bentley and Metz 2016) and over Europe (Martius et al 2008;Wirth and Eichhorn 2014), where they may contribute to the development of high-impact weather.…”