Convective indices for the central and western tropical Pacific

Abstract

Within the Pacific Air Forces (PACAF) area of responsibility, tropical deep convection that is not associated with tropical cyclones can cause significant impacts to operations. In this study, convective indices calculated from five sites in the central and western tropical North Pacific are examined with respect to their ability to predict the onset and intensity of deep convection. Two predictands are utilized: measures of convection derived from surface weather observations and the Naval Research Laboratory (NRL) Blended Rainrate estimates, which are derived from infrared and microwave satellite observations and interpolated to the five sites. Eighteen indices derived from rawinsondes are ranked by predictive skill for specific locations and seasons. Indices that exhibit significant skill are used in a discriminant analysis to define a multivariate experimental tropical convective index, which is then evaluated for each region and season. The multivariate index was not able to discriminate between convective and non-convective environments over the central North Pacific. Although the multivariate index exhibited skill for sites in the tropical western North Pacific during summer, it did not perform better than the highest-ranked single indices. For many of the locations and seasons evaluated, the Severe Weather Threat (SWEAT) Index exhibited the most skill.