Statistical prediction of TC frequency and seasonality within the core region of the inter american seas warm pool

This paper examines the potential predictability of TC frequency and intraseasonal variability in TC activity within the core region of the Inter American Seas warm pool, 1921-2008. A decision tree approach to seasonal forecasting for the joint region is presented with 1921-88 being the model development period and 1989-2008 being the test period for the prediction scheme.

The statistical reliability of an apparent out-of-phase relationship in TC activity in the nearshore EastPac and Gulf of Mexico-Caribbean is examined and shown to be linked to differences in the year-to-year seasonality of activity within the two ocean basins. A new TC seasonality statistic is defined for the study and this tri mean statistic of annual activity considers the median date of TC activity during the season (50% of the weighting) along with the dates by which 25% and 75% of the seasonal activity has occurred (each weighting 25%). Statistics for the two ocean basins indicate that ENSO, the PDO and local basin SSTs prior to the start of the respective basin season are linked to changes in TC frequency and intraseasonal variability. Seasonal timing in the two basins tends to be out of phase.

Additional analysis finds that since 1980 there has been a northward shift in the region of TC genesis in the EastPac and this northward shift appears linked to a long term strengthening of the South Pacific high and corresponding northward shift in the ITCZ south of Mexico. While the latitude of cyclogenesis has shifted northward towards the coast, the frequency in nearshore formation has decreased partly due to increased interaction with the rugged coast of southern Mexico.