Examination of the Unique Tropical Cyclone Climatology near Hispaniola and the Factors Influencing It

Using data from the National Hurricane Center's (NHC's) Best Track archive, it is found that there are local minima and maxima of occurrence of tropical cyclone (TC) activity in the southwest North Atlantic basin where sea-surface temperatures (SSTs) are rarely an inhibiting factor for development for the majority of the TC season. One area with unique variability in frequency is near Hispaniola. This region is characterized by relatively random TC motion and unique spatial variability in TC frequency between the western and eastern parts of the region. In this study, Hispaniola's TC climatology will be investigated from a mesoscale, a synoptic dynamical, and a climate perspective. It is known that terrain has an impact to both the motion of the TCs in other regions and basins (Bender et al. 1987, Huang et al. 2011, Ito et al. 2020), but it has not been well examined for the areas adjacent to the Caribbean Islands. Using the historical data from NHC's Best Track, the effects of the terrain on TC motion are shown for Hispaniola to better understand this regional variability in TC occurrence and motion. Findings show that channeling effects, asymmetric mid-level flow, and terrain-induced blocking of environmental steering all play a role in the direction and speed of TCs approaching the southern part of the island and after landfall. Fitzpatrick et al. 1995, Sadler 1976a & 1976b, and Wang et al. 2016 have shown that the Tropical Upper Tropospheric Trough (TUTT) is present during the summer season across the western regions of each major ocean basin. Although there is considerable variability, this trough is climatologically located west of Hispaniola, putting the island in the most cyclonic region of the trough. Utilizing data from the European Centre for Medium-Range Weather Forecasts (ECMWF) 5th Generation Reanalysis (ERA-5), the effects of the TUTT on this regional variability of occurrence will be examined. Findings show that regions of enhanced TC activity are mostly located near favorable locations of TC genesis and intensification within the TUTT while the opposite holds true for regions of suppressed TC activity. Using decadal means of atmospheric variables, results also reveal changes in the TUTT regional circulation over time, which may have further implications for regions of favorable locations of TC genesis and intensification in the future. TC genesis and intensification near Hispaniola does not appear to be affected by the NA TUTT. However, TC activity appears to have temporal variability. The AMO and NAO appear to be the most influential factors in TC activity near Hispaniola from relationships with the NA TUTT. By further understanding both perspectives to help explain this TC climatology, forecasts of TC intensity and track can be improved both on shorter and longer time scales. A better understanding of the TC climatology near Hispaniola is important given the large changes in US landfall probabilities across the region and the 50% probability line extending through the middle of the island.