Convective-Scale Simulations of Tropical Cyclones with the Met Office Unified Model

The Met Office (MO) has developed a high-resolution modelling system for tropical cyclones (TCs) that employs an automatically re-locatable domain, capable of simulating storms anywhere in the World, on demand.

As part of a programme of work with the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), this system has been used to re-run all storms that occurred in the Northwest Pacific basin in the latter part of 2013, at a horizontal resolution of 4.4km.

This paper presents results from this study, focussing on the performance of the 4.4km model relative to the MO Global Model (MOGM). It is shown that the regional model provides much better predictions for storm intensities (particularly for the most intense systems) and structure. However, there are some issues that require further work to address, namely that track forecasts are less accurate than the MOGM, there can be over-deepening at long lead times, and precipitation in storm cores is excessive relative to satellite observations.

One source of error in the 4.4km model is the weak bias in the global analyses used as initial conditions. In February 2015, a new technique to improve the initialisation of TCs in the MOGM was introduced, which involves the assimilation of central pressure estimates from TC warning centres. It is shown that this leads to improved regional model track (and also intensity) predictions, especially for the most severe storms.