Synoptic Structure and Evolution of a Kona Low

Abstract

A subtropical cyclone or kona low affected the island of Hawaii on 24?28 February 1997 and brought with it record winds at Hilo, large hail, blizzard conditions at higher elevations, and high surf. Damage estimates for the storm due to crop loss, property damage, and utility line destruction exceed $4 million. A detailed case study of the storm was conducted using all available operational data and data from the National Centers for Environmental Prediction?National Center for Atmospheric Research reanalysis dataset. The kona low formed on 23 February 1997 along a stalled trough northeast of the Hawaiian Islands and is investigated during five evolutionary stages: (i) incipient, (ii) intensifying, (iii) mature, (iv) weakening, and (v) dissipating. The system?s initial development is linked to dynamics at the 250-mb level. The maximum circulation, absolute vorticity, divergence, and height anomalies all occurred at 250 mb during the period of most rapid deepening. Cold anomalies occurred in a deep layer between 850 and 250 mb that tilted eastward with height. Quasigeostrophic analysis showed enhanced vorticity to the west of a thickness trough, a configuration that maintained an area of positive vorticity advection to the west of the surface low and over new convection east and southeast of the low. The vorticity tendency is dominated by the advection of vorticity aloft in this case, especially during the incipient and intensifying stages. The vorticity tendency is dominated by the generation of vorticity by divergence in the lower troposphere. Cloud bands with embedded convective cells formed on the low?s eastern side and propagated eastward, eventually leaving the area of synoptic-scale ascent and losing their convective properties. Areas where the best-lifted index values were less than zero and areas of positive low-level advection of equivalent potential temperature coincided with regions of deep convection, as inferred from satellite imagery.