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The impact of extratropical transition (ET) on tropical cyclone (TC) tornadoes is not fully understood with no prior tornado climatologies for ET cases. Hence, this study investigates how ET impacts tornadoes and convective-scale environments within TCs using multidecadal tornado and radiosonde data from North Atlantic TCs. This research divides ET into three phases: tropical (i.e., pre-ET), transition (i.e., during ET), and extratropical (i.e., post-ET). These results show that the largest portion of tornadoes occurs before and during ET, with the greatest frequencies during ET. As TCs progress through ET, tornado location shifts north and east in the United States but farther south or more strongly downshear right relative to the TC center. Tornadoes also tend to occur later in the day and are more likely to be associated with greater damage. Evaluation of radiosondes shows that the downshear-right quadrant of the TC is frequently the most favorable for tornado production, with sufficient entrainment CAPE (ECAPE) and strong storm-relative helicity (SRH). Specifically, the downshear-right quadrant shows slower decreases in ECAPE (associated with synoptic-scale cooling and drying) and increased SRH and associated lower-tropospheric vertical wind shear through ET, relative to the other quadrants relative to the deep-tropospheric (i.e., 850–200-hPa) vertical wind shear vector. These results inform the physical model and prediction of ET-related TC structure, both in terms of their convective-scale environments and subsequent hazard production.
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How Does the Relationship between Ambient Deep-Tropospheric Vertical Wind Shear and Tropical Cyclone Tornadoes Change between Coastal and Inland Environments?
Abstract This work investigates how the relationship between tropical cyclone (TC) tornadoes and ambient (i.e., synoptic-scale) deep-tropospheric (i.e., 850–200-hPa) vertical wind shear (VWS) varies between coastal and inland environments. Observed U.S. TC tornado track data are used to study tornado frequency and location, while dropsonde and radiosonde data are used to analyze convective-scale environments. To study the variability in the TC tornado–VWS relationship, these data are categorized by both 1) their distance from the coast and 2) reanalysis-derived VWS magnitude. The analysis shows that TCs produce coastal tornadoes regardless of VWS magnitude primarily in their downshear sector, with tornadoes most frequently occurring in strongly sheared cases. Inland tornadoes, including the most damaging cases, primarily occur in strongly sheared TCs within the outer radii of the downshear-right quadrant. Consistent with these patterns, dropsondes and coastal radiosondes show that the downshear-right quadrant of strongly sheared TCs has the most favorable combination of enhanced lower-tropospheric near-surface speed shear and veering, and reduced lower-tropospheric thermodynamic stability for tornadic supercells. Despite the weaker intensity farther inland, these kinematic conditions are even more favorable in inland environments within the downshear-right quadrant of strongly sheared TCs, due to the strengthened veering of the ambient winds and the lack of changes in the TC outer tangential wind field strength. The constructive superposition of the ambient and TC winds may be particularly important to inland tornado occurrence. Together, these results will allow forecasters to anticipate how the frequency and location of tornadoes and, more broadly, convection may change as TCs move inland.
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- Award ID(s):
- 2028151
- PAR ID:
- 10474842
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Weather and Forecasting
- Volume:
- 36
- Issue:
- 2
- ISSN:
- 0882-8156
- Format(s):
- Medium: X Size: p. 539-566
- Size(s):
- p. 539-566
- Sponsoring Org:
- National Science Foundation
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