Modeling Storm-Storm Interactions from the 2023 Hurricane Season with Multiple Moving Nests in HAFS

Previous work by Alaka et al. 2022 demonstrated forecast improvements in basin-scale HWRF when using multiple moving nests to resolve concurrent tropical cyclones. These improvements stemmed from better handling of storm-storm interactions due to improved initialization of multiple storms and from higher resolution simulation of the inner cores of all active tropical cyclones.

Multiple moving nests have been implemented in the Hurricane Analysis and Forecast System (HAFS) model codebase. We will use this capability to examine several cases from the 2023 hurricane season where more than one tropical cyclone was active in the North Atlantic basin at the same time. This basin configuration involves a parent domain at 6km horizontal resolution spanning the tropical North Atlantic and adjacent regions, with moving nests at 2km horizontal resolution centered on each tropical cyclone. Each tropical cyclone will be initialized using a combination of vortex initialization and inner core data assimilation.

Tropical Storm Philippe proved to be difficult to forecast, with large spread between various hurricane models and from run to run. Tropical Storm Rina was located to the east of Philippe during much of the time. We will examine whether initializing both storms in independent, high-resolution moving nests helps to improve the track and intensity statistics. The multiple moving nests runs will be compared to single storm moving nest forecasts with the same resolution and physics configuration.