Analysis of Environments Associated with TC Size and Structure Changes in the North Atlantic Basin

Tropical cyclones (TCs) can make dramatic size and structural changes during their lifetime, which can go on to impact their total damage potential if they make landfall. The radius of 34-kt winds (R34), which describes the overall size of the TC, can strongly impact the height of storm surge, which is one of the most devastating aspects of a landfalling TC. Size changes generally occur when environmental conditions are favorable or from dynamics internal to the TC. Focusing on the former, this study investigates the environments associated with significant size changes in the Atlantic Basin.

The exact environmental conditions under which TCs change size is still uncertain, but numerical modeling studies have generally found that high surface energy fluxes and atmospheric moisture play an important role in TC size expansion. TCs are also observed to change size as they move into higher latitudes and undergo extratropical transition. In this study, the extended Best track (EBT) archive is used to characterize cases of significant size increase and decrease, with particular focus on the R34. The data are filtered based on a robust set of criteria to ensure that influences from land and extratropical processes are minimized. Atmospheric quantities for each size-change case are extracted from ERA-Interim (ERA-I) global atmospheric reanalysis dataset and composited for analysis. When an empirical orthogonal function (EOF) analysis is applied to the 500-hPa height anomalies associated with each case, a clear separation occurs between cases of size change that occur near the deep tropics from those that occur in the extratropics.

Based on the EOF analysis, composites of various environmental quantities are examined for statistical significance in determining size changes of TCs. In this presentation we will examine the differences in those environmental quantities that are associated with size changes in the deep tropics compared with the extratropics and diagnose reasons for those differences.