The seasonal predictability of the wet season over Peninsular Florida

Abstract

AbstractIn this study, we examine the seasonal predictability of Peninsular Florida (PF)'s boreal summer season, which is also known as the PF wet season (PFWS) due to the coinciding peak of the robust seasonal cycle of rainfall. The seasonal predictability is examined in the Community Climate System Model, version 4 (CCSM4), which is one of the models of the North American Multi‐Model Ensemble used for routine, operational seasonal forecasts by the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC). An objective definition of the onset and the demise of the PFWS are then implemented, and the predictability of the onset, the demise and the seasonal rainfall anomaly is assessed from the CCSM4 seasonal hindcasts. Our study shows that the 33 years (1983–2015) of the CCSM4 seasonal hindcasts display very poor deterministic and probabilistic skill in predicting the onset and the demise of the PFWS and its seasonal rainfall anomalies for all lead times. It is shown that the seasonal hindcasts display poor skill for both the fixed calendar month and varying seasonal length of the PFWS. In many of these instances, the skills deteriorate with the lead time of the CCSM4 hindcasts, although, in some cases, they bear no relation (e.g., demise date of the PFWS). Our analysis reveals that the interannual variability of the location of the western ridge of the North Atlantic subtropical high is poorly rendered in the seasonal hindcast of CCSM4 with respect to reanalysis. This could explain the origins of some of the potential issues of the CCSM4 seasonal hindcasts with the variability of the PFWS.