Examination of the Mesoscale Environment and Associated Heavy Rainfall and Tornadoes Occurring During the US. East Coast Landfall of Hurricane Isaias (2020)

Allie Mazurek

Hurricane Isaias made landfall as a Category 1 storm, impacting the U.S. East Coast from 3-5 August 2020, bringing strong winds, storm surge, heavy rain, and tornadoes from North Carolina to New England. Despite the fast-moving nature of the system after landfall, Isaias still managed to produce heavy rainfall rates and flooding in some areas. Isaias was also a prolific tornado-producing tropical cyclone (TC), spawning 40 tornadoes across 7 states—including 8 that were rated EF2 or higher. Here, a brief synoptic analysis and a detailed mesoscale analysis of the system are presented. Thermodynamic, dynamic, and moisture fields are examined using datasets such as the RAP 13 km Analysis, archived soundings, and SPC Mesoanalysis data. Drawing on the analyzed environmental parameters, an ingredients-based approach is used to further assess the processes driving heavy rainfall and tornadoes associated with Isaias. The NCEP Stage IV gridded precipitation dataset and rain gauge data are used to identify locations with heavy precipitation and high rainfall rates, and tornado track and intensity information are collected from the NCEI Storm Events Database. Further, a comparison between characteristics of Isaias’s tornadoes and TC tornado climatology is presented using the TCTOR dataset, which is a full collection of tornadoes associated with 1995-2015 landfalling Atlantic TCs. Finally, a brief analysis and discussion on overlaps of these two hazards (i.e. tornadoes and flash floods) in Isaias is included.