A consensus track forecast for southern hemisphere tropical cyclones

Tropical cyclone (TC) track forecasting skill of operational numerical weather prediction (NWP) models and their consensus is examined for the southern hemisphere for the period 1992 to 2004. The TC track forecasting skill of the operational NWP models has been steadily improving. For the southern hemisphere, the typical 72 h model forecast error has decreased from roughly 550 km to 400 km over the past ten years and is now comparable to the typical 48 h model forecast error ten years ago. In this study we examine the performance of consensus aids that are formed whenever the TC track forecasts from at least two models from a specified pool of operational NWP models are available. The 72 h consensus forecast error has decreased from about 350 km to roughly 310 km over the past ten years. For a homogeneous dataset from the 2002-2004 seasons, the 72 h forecast errors for a consensus computed from a specified pool of 2, 3 and 5 models were 347, 342 and 312 km, respectively. While the addition of models to the consensus has a modest impact on forecast skill, it has a more marked impact on consensus forecast availability. For the 2002-2004 seasons, the forecast availability for 72 h consensus forecasts computed from a pool of 2, 3 and 5 models was 69%, 74% and 85%, respectively. Preliminary results using the 2003-2004 seasons indicate that the addition of two Australian models and a barotropic model increases the forecast availability by a few per cent at the 24 h, 48 h and 72 h forecast periods.