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.