Extended-range seasonal forecasts for the North Atlantic and North Pacific TCs with a hybrid dynamical-statistical model

A hybrid forecast model for seasonal hurricane activity in the North Atlantic is developed using a combined numerical coupled ocean-atmosphere climate and empirical prediction models. Based on a 29-yr (1981-2009) dataset, an empirical relationship is built on the number of seasonal hurricane and the large-scale variables from ECMWF hindcasts. The increase of seasonal hurricane activity correlates negatively with the sea surface temperature (SST) anomaly over the tropical East Pacific, positively with the SST anomaly over the Main Development Region (MDR) and North Atlantic and the decrease of wind shear over the MDR. The North Atlantic SST and the MDR vertical wind shear are selected as predictors based on sensitivity tests. Forecasts of these predictors are made with the ECMWF climate model run in ensemble mode thus providing a probability distribution of hurricane number. The forecast skill of the hybrid model is better or at least competitive than publicly-available forecast models but made with a one month earlier lead-time. The seasonal forecast for the North Pacific tropical cyclone activity is also examined. Forecasts are made for the coming season in both basins.