Tropical Transition of an Unnamed, High-Latitude, Tropical Cyclone
in the Eastern North Pacific
Alicia M. Bentley1 and Nicholas D. Metz2
1
Department of Atmospheric and Environmental Sciences
University at Albany/SUNY, Albany, NY 12222
2
Department of Geoscience
Hobart and William Smith Colleges, Geneva, NY 14456
Tropical cyclones (TCs) are not exclusive to the tropics. Modern-day satellite
observations have shown that TCs can develop in locations outside of tropical latitudes,
including nontraditional basins such as the South Atlantic and Mediterranean Sea. TCs
developing outside of tropical latitudes typically form via the tropical transition (TT)
process, during which an asymmetric, cold-core, extratropical cyclone (EC) transitions
into an axisymmetric, warm-core, TC. In early November 2006, an unnamed TC formed
via the TT process at ~40°N over the eastern North Pacific. An EC, developing
downstream of a thinning upper-tropospheric trough over the Gulf of Alaska, 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 region
historically devoid of TC activity.
This presentation identifies the upper- and lower-tropospheric features linked to
the formation of the EC that transitions into the unnamed TC, as well as provides a
synoptic overview of the features and processes associated with the unnamed TC’s TT.
As observed in previous TT studies, 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 prior to the isolation of its warm core. Weather Research and
Forecasting (WRF) model simulations will be used to investigate the mesoscale processes
occurring during the unnamed TC’s TT that were not captured by observations. WRF
model simulations will also be used to explore the differences in TC structure and
intensity that can arise from changing the complexity of the microphysical
parameterization scheme used to simulate the TT process.