Tropical cyclone variability over the North Atlantic: Observations and high-resolution simulations

Interannual-decadal variability of tropical cyclone (TC) track density over the North Atlantic (NA) between 1979 and 2008 is examined using TC best-track data from the National Hurricane Center and TC tracks detected from model simulations; the simulations are from a 25-km-resolution version of the High Resolution Atmospheric Model (HiRAM) forced by observed sea surface temperatures (SSTs). For both observed and simulated TCs, we study the variability in their track density separately for decadal and interannual timescales, in order to gain a better understanding. For each timescale, we identify the leading modes by means of empirical orthogonal function analysis, and understand them via exploring the underlying SST pattern and large-scale atmospheric factors (e.g., low-level vorticity and vertical wind shear). We also characterize the temporal evolutions of the relative proportion of TC track density over different regions on the two different timescales, and link them respectively to various modes of climate variability (e.g., the North Atlantic Oscillation). A comparison between the observations and the simulations suggests that HiRAM captures these observed features. We will further discuss the internal variability and accordingly the predictability of NA TC track density, particularly that related to landfall, based on HiRAM ensemble simulations.