Utilizing Velocity Azimuth Displays to Analyze Ocean-to-Land Differences in the Tropical Cyclone Wind Profile and Their Impacts on Tornadogenesis

Tropical cyclones (TC) are a well-known natural hazard that frequently impact coastal cities around the world. However, while people commonly associate high winds, storm surges, and flooding with TCs, there is one hazard that tends to be overlooked – tornadoes (TOR). Even though TORs are another common natural hazard, the general public does not always realize that TCs can produce TORs (hereafter referred to as TC TORs). While TC TORs do not tend to be as strong as TORs produced by supercells or quasi-linear convective systems (QLCS), they do still threaten lives and property. Furthermore, forecasting and diagnosing TC TORs pose their own unique challenges to the meteorological community (e.g., a “velocity couplet” for a TC TOR might not be as prevalent on radar imagery as it sometimes is for a TOR produced by a supercell or by a QLCS). This presentation will focus on a case study of Tropical Storm (TS) Fay from 2008, a TC that produced multiple TORs in the United States.

Before TS Fay made its third Floridian landfall, atmospheric science researchers from the University of Alabama in Huntsville (UAH) deployed to a site near Jacksonville, FL to monitor atmospheric conditions before, during, and after the storm. During the 57 hours of continuous data collection, the UAH researchers were able to sample a tornadic rainband that produced at least one confirmed TOR. To illustrate how a TC wind profile changes across a coastal region, this presentation will compare velocity azimuth display (VAD) profiles from the UAH Mobile Alabama X-Band (MAX) research radar and the Weather Surveillance Radar 1988 Doppler radar in Jacksonville, FL (KJAX). Because MAX sampled on-shore flow while KJAX was farther inland over a rougher surface, the TS Fay deployment is an ideal case to examine how the 0-1 km storm relative helicity (SRH) changed between MAX and KJAX. For example, the VAD profiles indicated significant reductions in wind speed below several hundred meters at KJAX as opposed to MAX, leading to higher 0-1 SRH values at KJAX. In this presentation, the implications of the differences between MAX and KJAX on tornadogenesis will be discussed.