Recent Unusual Consecutive Spring Tropical Cyclones in North Atlantic and Winter Oceanic Precursor Signals

Although the North Atlantic (NA) hurricane season has been reported to start increasingly early, historical long-term changes in NA spring tropical cyclone (TC) activity have not been examined in previous studies. We find that spring TCs have become more frequent and intense, and they have more closely approached the US coastline over the past four decades, thus increasing the probability of landfall. A long-term increase in the NA sea surface temperature (SST) and northward incursion of warm water may be responsible for the increasing number, intensity, and northward shift of spring TCs. In addition, the interdecadal winter NA SST tripole mode may induce a North Atlantic Oscillation (NAO)-like atmospheric response in the following spring, which controls spring TC tracks via modulating the strength and position of the NA subtropical high (or the Bermuda high). The superposition of the interdecadal positive winter SST tripole on the NA warming trend has contributed to the anomalous enhancement and northward shift of spring TC activity, increasing the spring TC risks in the US in the past six years.