Doppler Radar and Storm Environment Observations of a Maritime Tornadic Supercell in Sydney, Australia

A long-lived offshore supercell tracked northward parallel to the coastline during the morning of 16 December 2015 and produced an EF-2 tornado as it briefly crossed land ~4 kilometers south of Australia’s busiest airport in Sydney. The tornado passed within ~2 kilometers of the Kurnell C-band Doppler radar and a 59 m s^-1surface wind gust was recorded shortly afterwards by the Kurnell Automated Weather Station.

A cool moist onshore flow regime was characterized by surface air temperatures that barely exceeded 21^o Celsius and relatively high dewpoint temperatures in the 16-20^oC range. Onshore low-level parcel trajectories experienced positive sea surface temperature anomalies of up to +2^oC. The coldest observed surface parcel in the storm’s rear flank downdraft prior to the tornado experienced a virtual potential temperature deficit of only 4^oC as both temperature and dewpoint temperature decreased only by a few degrees within the downdraft. A north-northeasterly storm motion vector with ambient north-northeasterly low-level flow at tornado time augmented the storm’s 0-1 km storm-relative helicity values.

This study will characterize the environment of the tornadic storm prior to and during the tornado, and explore the reasons how tornadogenesis was promoted during the late morning from inflow sourced from a normally unfavorable marine environment. A radar analysis of the storm, including Dual-Doppler wind fields, will also be presented.