Tropical cyclone occurrence dates in the North Atlantic and eastern North Pacific basins: climatology, trends, and correlations with overall seasonal activity

Tropical cyclones (TCs) are major meteorological hazards for coastal communities around the world. Among the most active TC development basins are the North Atlantic (NATL) and the eastern North Pacific (ENP), both of which bring impacts to the USA and other countries of North America. This research assesses the climatology of occurrence dates of nth (e.g., 1st and 2nd,) TCs and hurricanes in both basins, as well as occurrence dates of accumulated cyclone energy thresholds. We use statistical methods to develop a base climatology of occurrence dates and assess their trends over time, as well as correlate early season nth TC and hurricane occurrence dates with overall seasonal activity. We find that the climatologies of NATL and ENP occurrence dates exhibit similarities but unique differences that relate to the TC climatologies of their basins. In addition, we find that NATL nth TC occurrence dates generally have been trending earlier with time, while no trends were identified for the ENP or for hurricanes in either basin. Lastly, we find that early season TCs possess the ability to postulate overall seasonal activity in both basins, the strongest correlations in each basin coming from the 3rd and 4th TCs in the NATL and the 5th and 6th TCs in the ENP. Results of this study have utility in improving seasonal TC forecasts for the NATL and ENP made by 1 September and 1 August, respectively, as well as providing a baseline for modeling studies.

Automated summary

This research assesses the climatology of tropical cyclone occurrence dates in the North Atlantic and eastern North Pacific, finding trends and correlations with early season activity. Results show that occurrence dates of TCs in the North Atlantic have been trending earlier, while no trends were identified for the eastern North Pacific or hurricanes in both basins. Early season TCs can predict overall seasonal activity, with the strongest correlations found in the 3rd and 4th TCs in the North Atlantic and the 5th and 6th TCs in the eastern North Pacific.