Structures of Mesocirculations Producing Tornadoes Associated with Tropical Cyclone Frances (1998)

Abstract

Radar structures of one mesocyclone and one mesocirculation (the term mesocirculation refers to a class of rotating updrafts, which may or may not be as spatially and temporally large as a typical mesocyclone) that developed a total of four tornadoes in association with Tropical Cyclone (TC) Frances 1998 are presented. One tornado developed within an inner rainband near the time of landfall while three of the other tornadoes developed within an outer rainband nearly 24 hours after the landfall. Radar reflectivities of the tornadic circulations averaged upwards of 40 dBZ while Doppler radar wind components directed toward the radar averaged 11m s)1. It is realized that although TC Frances was a minimal hurricane it spawned several tornadoes (four of which were studied) causing damage exceeding $2 million. These tornadoes were not all located close to the TC center, serving as a caution to forecasters and emergency personnel that the immediate landfalling area is not the only place to watch.While it is difficult to accurately predict the TC tornado location and time of occurrence, the degree of low-level baroclinicity seems to play an important role in tornadogenesis. Another significant finding is that the tornadoes were produced on the inward side of an inner rainband, as well as the inward side of an outer rainband. Consistent with climatology, the forward right quadrant of the TC developed the four tornadoes studied here.

Miniature Supercells in an Offshore Outer Rainband of Hurricane Ivan (2004)

“…Indeed, prior studies have demonstrated that offshore environments can be conducive to supercell formation (Bogner et al 2000;Baker et al 2009), documented offshore supercells using coastal Doppler radars (Spratt et al 1997;Rao et al 2005;Lee et al 2008), and noted reports of waterspouts and tornadoes within a few kilometers of the coastline (Gentry 1983;Hagemeyer 1997). This paper contributes to such evidence by providing the first detailed observations of tropical cyclone miniature supercells located more than 100 km offshore and beyond the Doppler range of operational coastal radars.…”

Convective Modes for Significant Severe Thunderstorms in the Contiguous United States. Part III: Tropical Cyclone Tornadoes

“…More recently, applied research has expanded the TC tornado knowledge base into realms such as numerical modeling (e.g., McCaul and Weisman 1996;Morin et al 2010) and Doppler radar examinations of tornadic storms (e.g., Spratt et al 1997;McCaul et al 2004;Rao et al 2005). Agée and Hendricks (2011) associated the presence of Doppler radar with a large increase in TC tomado reports specific to Florida (i.e.. pre-Doppler era tomadoes were "severely underestimated" in that state).…”

Choosing a universal mean wind for supercell motion prediction

“…Another possible modification to the mean wind applies to low-topped, miniature, or "shallow" supercells (e.g., Davies 1990Davies , 1993. Arguably these are less common than the prototypical Great Plains supercell, except in tropical cyclones (e.g., McCaul and Weisman 1996;Spratt et al 1997;Rao et al 2005;Edwards et al 2012). Still, they can produce substantial severe weather, including tornadoes (e.g., Grant and Prentice 1996;McCaul and Weisman 1996;Wicker and Cantrell 1996;Jungbluth 2002;Darbe and Medlin 2005;Graham 2007;Richter 2007;among others).…”