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Subseasonal Tropical Cyclone Prediction and Modulations by MJO and ENSO in CESM2

Presentation Date
Monday, December 12, 2022 at 9:40am - Monday, December 12, 2022 at 9:50am
McCormick Place - E354a



Subseasonal tropical cyclone (TC) reforecasts from the Community Earth System Model version 2 (CESM2 (CAM6)) subseasonal prediction system are examined in this study. We evaluate the modeled TC climatology and the probabilistic forecast skill of basin-wide TC genesis at weekly temporal resolution. Prediction skill is calculated using the Brier skill score relative to a constant annual mean climatology and to a monthly-varying seasonal climatology during TC season. The model captures the observed basin-wide climatological TC seasonality and spatial distributions at weeks 1-6, but TC genesis is largely underestimated from week 2 onward. The predicted TC genesis is primarily controlled by the number of TC “seeds” and, to a lesser extent, the mean-state climate condition, which mainly consists of compensations between the positive effects from relative humidity and the negative effects from wind shear. The model has good prediction skill relative to the constant climatology across all the basins and lead times, but is only skillful in the eastern Pacific, North Indian Ocean and Southern Hemisphere at week 1 when compared to the seasonal climatology, indicating limited skill in predicting deviations from the seasonal cycle. We find strong modulations of the predicted TC genesis at up to 3 weeks of forecast lead time by the Madden-Julian Oscillation. The interannual variability of predicted TC genesis and accumulated cyclone energy are skillfully predicted in the North Atlantic and the Northwestern Pacific, with a strong modulation by the El Nino-Southern Oscillation.

Funding Program Area(s)