Seasonal hurricane outlooks, such as those issued by NOAA’s Climate Prediction Center, Colorado State University (Klotzbach et al., 2017), European Center for Medium-Range Weather Forecasts, and University of Arizona (Davis and Zeng, 2019), produce skillful (i.e.,. better than climatology) seasonal forecasts of overall North Atlantic tropical cyclone (TC) activity. Such forecasts are possible because seasonal hurricane activity is largely modulated by several climate modes of tropical Atlantic and Pacific atmosphere–ocean variability (e.g., El Niño – Southern Oscillation (ENSO), Atlantic Meridional Mode (AMM), and Atlantic Niño/Niña) that can be predicted before the Atlantic hurricane season begins in June 1st. However, Atlantic TC activity is not always homogeneous throughout the basin, with regional impacts varying from season to season. For example, the 2002 Atlantic hurricane season featured below-normal activity (i.e., less than 70% of the 1950–2000 median Accumulated Cyclonic Energy (ACE)). However, seven out of the total 12 tropical storms made landfall in the continental US. In contrast, the 2023 season saw above-average TC activity and 20 named storms (exceeding the 1991–2020 average of 14), but only three U.S. landfalls occurred. Therefore, there is room for improving the current operational seasonal hurricane outlooks.
Given that each mode of TC-related tropical climate variability (i.e, ENSO, AMM, and Atlantic Niño/Niña) has unique seasonality and region of major influence, a new study published in Weather and Forecasting (West et al., 2025) utilized sea surface temperature (SST) predictors associated with tropical climate modes to forecast TC activity in five Atlantic sub-basins, namely, (1) Caribbean, (2) U.S. Gulf Coast, (3) U.S. East Coast, (4) subtropical North Atlantic, and (5) tropical North Atlantic (see Figure).
The study identified skill in forecasting seasonal sub-basin ACE for above- and below-normal seasons using SST predictors from the North American Multi model Ensemble, with the most substantial probabilistic forecast skill for the Caribbean. Specifically, the forecast skill of above-normal ACE was greatest for the Caribbean sub-basin, while the skill of below-normal ACE was greatest in the subtropical North Atlantic. All sub-basin below- and above-normal probabilistic forecasts had useful skill as determined by the Relative Operating Characteristic (ROC) skill scores of 0.7 or higher, except the below-normal ACE forecast for the U.S. Gulf Coast, and the above-normal ACE forecast for the subtropical North Atlantic. Overall, there were marginal improvements in forecasting sub-basin seasonal TC activity when compared with a “full-basin” forecast. Nevertheless, strong correlations between the sub-basin forecasts limited the predictive usefulness, except for the Caribbean sub-basin. The study further discussed the challenges and the road map toward improving the North Atlantic sub-basin TC prediction skill.
Figure 2 from West et al. (2025): (a) Sub-basins of Atlantic TC activity, represented by black boxes in clockwise order from the top left: U.S. East Coast (EUS), subtropical North Atlantic (SNA), tropical North Atlantic (TNA), Caribbean (CAR), and U.S. Gulf Coast (GLF). (b) Matrix of Pearson correlation coefficients computed between the observed ACE of the five sub-basins and North Atlantic (NATL) basin ACE during the 1966–2023 June-November period. White boxes correspond to correlation coefficients that are not significant at the 95% confidence level based on the Student’s t test.
West, R., H. Lopez, S. Lee, D. Kim, A. E. Mercer, G. R. Foltz, and H. Wang, 2025: Subbasin Forecasts of Seasonal Atlantic Hurricane Activity: Skill and Challenges. Wea. Forecasting, 40, 2225–2238. https://doi.org/10.1175/WAF-D-24-0098.1
Klotzbach, P.J., Saunders, M.A., Bell, G.D. and Blake, E.S. (2017). North Atlantic Seasonal Hurricane Prediction. In Climate Extremes (eds S.-Y.S. Wang, J.-H. Yoon, C.C. Funk and R.R. Gillies). https://doi.org/10.1002/9781119068020.ch19
Davis, K., and X. Zeng, 2019: Seasonal Prediction of North Atlantic Accumulated Cyclone Energy and Major Hurricane Activity. Wea. Forecasting, 34, 221–232. https://doi.org/10.1175/WAF-D-18-0125.1
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