An evaluation of tropical cyclone forecast in the Southwest Indian Ocean basin with AROME-Indian Ocean convection-permitting numerical weather predicting system

In order to contribute to ongoing efforts on tropical cyclone (TC) forecasting, a new, convection-permitting, limited-area coupled model called AROME-Indian Ocean (AROME-IO) was deployed in the Southwest Indian Ocean basin (SWIO) in April 2016. The skill of this numerical weather predicting system for TC prediction is evaluated against its coupling model (European Center for Medium Range Weather Forecasting-Integrated Forecasting System [ECMWF-IFS]) using 120-hr reforecasts of 11 major storms that developed in this area over TC seasons 2017-2018 and 2018-2019. Results show that AROME-IO generally provides significantly better performance than IFS for intensity (maximum wind) and structure (wind extensions, radius of maximum wind) forecasts at all lead times, with similar performance in terms of trajectories. The performance of a prototype, 12-member ensemble prediction system (EPS), of AROME-IO is also evaluated on the case of TC Fakir (April 2018), a storm characterized by an extremely low predictability in global deterministic and ensemble models. AROME-IO EPS is shown to significantly improve the predictability of the system with two scenarios being produced: a most probable one (~66%), which follows the prediction of AROME-IO, and a second one (~33%) that closely matches reality.