ENSO plays little role in early-season Atlantic hurricane activity

This is a guest blog by Robert West. Robert is a postdoctoral research associate in the Northern Gulf Institute (NGI) at the Mississippi State University and is also affiliated with NOAA’s Atlantic Oceanographic and Meteorological Laboratory.

Differences in sea surface temperature anomalies (SSTAs) between the tropical Atlantic and Pacific oceans are known to influence atmospheric circulation patterns that modulate Atlantic hurricane activity. For instance, El Niño in the Pacific causes tropospheric warming over the tropical Atlantic increasing atmospheric static stability and thus suppressing the formation and development of tropical cyclones over the Atlantic hurricane main development region, and vice versa for La Niña. In a paper recently accepted to Geophysical Research Letters, a team of researchers, led by Robert West, finds that the relative influence of tropical interbasin SSTAs on Atlantic accumulated cyclone energy (ACE) varies throughout the hurricane season (June-November). While SSTAs in the Atlantic main development region (MDR) and the Pacific Niño 3 region were found to be equally important for late-season (September-November) hurricane activity, early-season (June-August) ACE is largely impacted by MDR SSTAs.
The seasonality of interbasin SST influence on Atlantic hurricane activity reflects periods of increased tropical SST variability. In the early-season, increased SSTA variability in the tropical North Atlantic is coincident with the spring variance peak of the Atlantic meridional mode, while increased variability of tropical Pacific SSTAs in the late-season is consistent with a November-December maximum due to El Niño – Southern Oscillation (ENSO) phase-locking to the seasonal cycle. The team also developed an MDR-Niño 3 interbasin SST index that produces skillful seasonal forecasts of above- and below-average ACE using SST predictors from the North American Multi-Model Ensemble (NMME). The prediction skill for MDR SSTAs was found to be lower than that of Niño 3 SSTAs, suggesting that increasing the prediction skill for MDR SSTAs is key to improving seasonal outlooks.

West, R., Lopez, H., Lee, S.-K., Mercer, A., Kim, D., Foltz, G., & Balaguru, K. (2022). Seasonality of interbasin SST contributions to Atlantic tropical cyclone activity. Geophysical Research Letters, 49, e2021GL096712. https://doi.org/10.1029/2021GL096712