Wind turbines subjected to extreme events, including typhoons, will experience large structural responses that may lead to components failure, due in part to the high wind speeds, high turbulence and rapid changes in wind direction induced by the extreme event. As floating offshore wind turbines experience larger motions and more unsteady flow conditions than their bottom-fixed counterparts, it is essential to understand the possible impact that an extreme event may have on the turbine loads and response. In this study, the Simulator fOr Wind Farm Applications (SOWFA) developed by NREL is used to investigate the potential of a computational fluid dynamics method using Large Eddy Simulation in OpenFOAM for simulating the response of a floating wind turbine in an extreme typhoon event using measured typhoon conditions. The turbine is modelled using an actuator line method coupled with NREL's aeroelastic code FAST. To validate this approach, the simulated platform motions and tower bending moments from the numerical study are compared against experimental data from the Goto Islands floating offshore wind turbine demonstration project, where a 100kW spar type turbine installed at sea survived the extreme typhoon event Sanba with no damage to the structure. Following the validation of the SOWFA-FAST coupling for a typhoon event, this approach is then applied to a 5 MW floating wind turbine to investigate the impact of extreme environmental conditions on the blade and tower response of a full scale FOWT. This work provides information on the design requirements of FOWTs in sites where typhoon conditions are a frequent occurrence, and will be used in future work to improve the rotor design of FOWTs to ensure survival in extreme conditions.