Toward Using the CPC's Velocity Potential MJO Index for Probabilistic Tropical Cyclone Prediction

NOAA's Climate Prediction Center (CPC) utilizes an MJO index (VPI) based on a ten phase categorization of 200-hPa velocity potential anomalies. The VPI may have an advantage over the Wheeler-Hendon MJO index (RMM) when analyzing tropical cyclone formation, especially during the boreal summertime, due to its emphasis solely on the upper-level divergent circulation. The focus of this study was to determine if the VPI could be shown to modulate the climatological tropical cyclone genesis probabilities in seven tropical basins (Atlantic, Eastern Pacific, Central Pacific, Western Pacific, Northern Indian Ocean, southern Indian Ocean, and South Pacific). The datasets used for analysis were best track data from the Joint Typhoon Warning Center (JTWC) and National Hurricane Center (NHC) HURDAT2. Basin climatology, by pentad, was an important reference for comparison between the null and intraseasonal effects of the MJO on tropical cyclone genesis. Analysis of the probability of tropical cyclone formation relative to the seasonal climatology yields a useful tool for subseasonal forecasts of tropical cyclogenesis.