In JMA, The Seasonal Ensemble Prediction System (Seasonal EPS) is operated to support issuing one-month, three-month and warm/cold season forecasts as well as El Niño monitoring and outlook. The numerical prediction model used in the Seasonal EPS is a coupled ocean-atmosphere general circulation model (CGCM), which consists of the AGCM (based on a low-resolution version of the GSM) and the ocean general circulation model (OGCM). The specifications of the Seasonal EPS are shown in the following table.
| Seasonal EPS (JMA/MRI-CPS4) | |
| Last upgrade | January 2026 for one-month prediction February 2026 for three-month and warm/cold season prediction |
| Model | Coupled ocean-atmosphere general circulation model (JMA/MRI-CPS4) |
| Atmospheric general circulation model (AGCM) |
JMA-GSM with wide-ranging updates for CPS4 Horizontal resolution: TL319 (approx. 55 km) Vertical levels: 128 levels up to 0.01 hPa |
| Oceanic general circulation model (OGCM) |
MRI.COM Horizontal resolution: 0.25º x 0.25º Vertical levels: 60 levels |
| Integration range | up to 7 months |
| Initial conditions | Atmosphere: JMA Global Analysis and Ozone Analysis Ocean: MOVE/MRI.COM-G3 (Low-res. 4DVAR + High-res. downscaling) Sea ice: MOVE/MRI.COM-G3 (3DVAR) Land: Offline model runs (forced by JRA-3Q and JMA Global Analysis) |
| Boundary conditions | SST: One-tier method Sea ice: Interactive Sea ice model |
| Ensemble Perturbation method | Combination of Singular vectors (SVs) and Local Ensemble Transform Kalman Filter (LETKF), Stochastic Perturbation of Physics Tendency (SPPT) and Stochastic Humidity Profile for Convective parametrization (SHPC), and Lagged Average Forecast (LAF) |
| Ensemble size | 50 for one-month prediction 85 for three-month and warm/cold season prediction |
| Freq. of model product creation | Once a week for one-month prediction Once a month (around 20th of every month) for three-month and warm/cold season prediction (Model operation) |
| Hindcast period | Jan 1991 - Dec 2020 |
| Hindcast ensemble size | 13 / initial date for one-month prediction 10 / month for three-month and warm/cold season prediction |