Met Office Global Model tropical cyclone performance following a major model upgrade and new initialisation technique

In July 2014 a major upgrade to the Met Office Global Model (MOGM) was implemented. This included the introduction of the ‘ENDGame' dynamical core, improved physics and increased horizontal resolution to about 17 km at mid-latitudes. Following implementation, the MOGM's tropical cyclone (TC) track forecast errors dropped dramatically to levels never seen before during both the 2014 northern hemisphere and 2014-15 southern hemisphere seasons. Furthermore, a large weak bias in the model's TC forecasts was reduced and almost eliminated at longer lead times.

In February 2015 a new technique to help initialise TCs in the MOGM was introduced, which involves assimilation of central pressure estimates from TC warning centres. Since implementation there has been a further reduction in TC track forecast errors. The change has also resulted in further reductions to the model's weak bias. In particular, the weak bias in the analysis and short lead time forecasts, which had not been greatly affected by the model change in July 2014, was much reduced.

This paper will present details of these two changes and the performance of the MOGM since they were implemented.