Reduction in Uncertainty in Tropical Cyclone Track Forecasts over the North Indian Ocean

Over the North Indian Ocean (NIO) basin, the uncertainty in tropical cyclone (TC) track forecast is depicted by constructing a cone of uncertainty (COU) around the forecast track for the benefit of disaster managers in their decision-making, especially with respect to area of evacuation. The COU is constructed by drawing a tangent to the circles with the radii equal to average track forecast errors during the past five years for forecast times of 12, 24, 36, …, up to 120 h. The COU which is revised periodically to reflect the track forecast accuracy, has been recently revised by India Meteorological Department (IMD) from the post-monsoon season of 2014. Hence, a study has been undertaken to evaluate this newly introduced COU forecast by IMD. The revised radii used to construct the COU have shrunk by 20-30% due to improved TC track forecast in the recent years (2009-2013). For the new COU, the radii of circles for 24, 48, 72, 96 and 120 h forecasts are 65, 105, 140, 170 and 200 nm respectively, against 80, 135, 185, 235 and 285 nm for the previous COU (2009-2013). The accuracy of the newly constructed forecast COU is 70-80% and is comparable with those of other leading TC forecasting centres in the world.