The effect of ensemble-transform SST perturbations on tropical-cyclone track forecasts in a medium-range global NWP forecast ensemble

Analysis perturbations of sea-surface temperature (SST) are generated by implementing the ensemble transform (ET) analysis perturbation scheme (McLay et al. 2008, Wei et al. 2008) in conjunction with a prognostic sea-surface temperature (SST) formulation (Zeng and Beljaars 2006) in the Navy Operational Global Prediction System (NOGAPS). Previous work with forecast ensembles of 32 members and horizontal resolution T119 has shown that inclusion of the SST perturbations can lead to improved ensemble-mean and probability forecasts related to 10m wind speed (McLay 2009). This work looks specifically at how inclusion of the SST perturbations affects the skill of the NWP-ensemble tropical-cyclone track forecasts. In particular, forecast ensembles of 16 members and horizontal resolution T159 are generated for the test period 26 June 2008 00UTC to 31 August 2008 00UTC. Track forecasts from the ensemble with SST perturbations are compared against track forecasts from a baseline ensemble without SST perturbations.