Radar Signatures of Tropical Cyclone Tornadoes in Central North Carolina

Douglas Schneider National Weather Service Forecast Office, Morristown, Tennessee

Search for other papers by Douglas Schneider in
Current site
Google Scholar
PubMed
Close
and
Scott Sharp National Weather Service Forecast Office, Raleigh, North Carolina

Search for other papers by Scott Sharp in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

During the tropical cyclone season of 2004, there were four tropical cyclones that spawned tornadoes in central North Carolina: Frances, Gaston, Ivan, and Jeanne. This study examines the environmental characteristics and radar signatures from these events. The tornado warning decision-making process is a difficult one during any severe weather event, but it is even more difficult in a tropical cyclone environment because of the subtlety of features and rapid tornadogenesis that can occur. Previous studies that have examined the characteristics of a tropical cyclone environment found that high low-level moisture content, high shear, and a midlevel intrusion of dry air are favorable for tornadoes. The tropical cyclones that are examined in the current study all exhibited these characteristics. Radar signatures associated with these tornadoes were more subtle and weaker when compared with nontropical cyclone tornadoes, but were still discernable. This study analyzed the radar signatures from tornadic and nontornadic storms in a tropical cyclone environment with the purpose of determining the best indicators of tornadogenesis. Three precursors were found to give good lead time for tornado touchdowns: 1) a near gate-to-gate mesocyclone rotational velocity of 20 kt (10.3 m s−1) or greater, 2) a hook or appendage signature in the reflectivity data, and 3) the presence of a velocity enhancement signature of 30 kt (15.4 m s−1) or greater between 7000 ft (2.1 km) and 14 000 ft (4.2 km) AGL. Using these signatures together in the tornado warning decision-making process can increase lead time and accuracy in the tropical cyclone environment.

Corresponding author address: Douglas Schneider, 5974 Commerce Blvd., Morristown, TN 37814. Email: douglas.schneider@noaa.gov

Abstract

During the tropical cyclone season of 2004, there were four tropical cyclones that spawned tornadoes in central North Carolina: Frances, Gaston, Ivan, and Jeanne. This study examines the environmental characteristics and radar signatures from these events. The tornado warning decision-making process is a difficult one during any severe weather event, but it is even more difficult in a tropical cyclone environment because of the subtlety of features and rapid tornadogenesis that can occur. Previous studies that have examined the characteristics of a tropical cyclone environment found that high low-level moisture content, high shear, and a midlevel intrusion of dry air are favorable for tornadoes. The tropical cyclones that are examined in the current study all exhibited these characteristics. Radar signatures associated with these tornadoes were more subtle and weaker when compared with nontropical cyclone tornadoes, but were still discernable. This study analyzed the radar signatures from tornadic and nontornadic storms in a tropical cyclone environment with the purpose of determining the best indicators of tornadogenesis. Three precursors were found to give good lead time for tornado touchdowns: 1) a near gate-to-gate mesocyclone rotational velocity of 20 kt (10.3 m s−1) or greater, 2) a hook or appendage signature in the reflectivity data, and 3) the presence of a velocity enhancement signature of 30 kt (15.4 m s−1) or greater between 7000 ft (2.1 km) and 14 000 ft (4.2 km) AGL. Using these signatures together in the tornado warning decision-making process can increase lead time and accuracy in the tropical cyclone environment.

Corresponding author address: Douglas Schneider, 5974 Commerce Blvd., Morristown, TN 37814. Email: douglas.schneider@noaa.gov

Save
  • Curtis, L., 2004: Midlevel dry intrusions as a factor in tornado outbreaks associated with landfalling tropical cyclones from the Atlantic and Gulf of Mexico. Wea. Forecasting, 19 , 411427.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Markowski, P. N., Straka J. M. , and Rasmussen E. N. , 2002: Direct surface thermodynamic observations within the rear-flank downdrafts of nontornadic and tornadic supercells. Mon. Wea. Rev., 130 , 16921721.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCaul E. W. Jr., , 1991: Buoyancy and shear characteristics of hurricane–tornado environments. Mon. Wea. Rev., 119 , 19541978.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCaul E. W. Jr., , and Weisman M. L. , 1996: Simulations of shallow supercell storms in landfalling hurricane environments. Mon. Wea. Rev., 124 , 408429.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCaul E. W. Jr., , and Cohen C. , 2002: The impact on simulated storm structure and intensity of variations in the mixed layer and moist layer depths. Mon. Wea. Rev., 130 , 17221748.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • McCaul E. W. Jr., , Buechler D. E. , Goodman S. J. , and Cammarata M. , 2004: Doppler radar and lightning network observations of a severe outbreak of tropical cyclone tornadoes. Mon. Wea. Rev., 132 , 17471763.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rasmussen, E. N., and Blanchard D. , 1998: A baseline climatology of sounding-derived supercell and tornado forecast parameters. Wea. Forecasting, 13 , 11481164.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Spratt, S. M., Sharp D. W. , Welsh P. , Sandrik A. , Alsheimer F. , and Paxton C. , 1997: A WSR-88D assessment of tropical cyclone outer rainband tornadoes. Wea. Forecasting, 12 , 479501.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thompson, R. L., Edwards R. , Hart J. A. , Elmore K. L. , and Markowski P. , 2003: Close proximity soundings within supercell environments obtained from the Rapid Update Cycle. Wea. Forecasting, 18 , 12431261.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Vescio, M. D., Weiss S. J. , and Ostby F. P. , 1996: Tornadoes associated with Tropical Storm Beryl. Natl. Wea. Assoc. Dig., 21 , 1. 210.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 407 130 17
PDF Downloads 354 109 18