A Kona low brought a series of strong thunderstorms to the Hawaii Islands lasting from late on the 17th to late on the 19th. The storms resulted in the issuance of severe thunderstorm watches and warnings, flash flood advisories and warnings, and special marine warnings. Thunderstorms produced gusty winds, small hail, and heavy rainfall, and caused many to lose power.
Water Vapor imagery with NWP 500 mb height and wind speed overlaid showed the evolution of the robust mid-latitude cyclone as it dipped southeast from well north of the islands, and associated thunderstorms developed and moved west to east across the state. The Jet as analyzed in the model data is appropriately located over a region of fast moving clouds/moisture features and a sharp T gradient as observed in water vapor imagery. From NWS HFO early on the 18th: “Satellite imagery shows an impressive mid-latitude cyclone deepening over the Central Pacific Basin as digs southward toward the islands.” and in the afternoon of the 18th: “On satellite, we can already see the deep trough quickly approaching the state with a line of thunderstorms developing ahead of the front.”
One can leverage the Airmass RGB imagery to diagnose areas of descending stable stratospheric (high PV) air into the troposphere, which appear as red in the RGB. Overlaying isobars of the 1.5 PVU surface provides a quantitative proxy for the dynamic troposphere location, or where stratospheric air is dipping into the troposphere (high pressure areas). The high pressure PVU areas of the NWP field match up well with the satellite observations, and indicate a region favorable for cyclogenesis.
An animation of VIS/IR sandwich (day) and IR (night) imagery focused on the islands captures the evolution of thunderstorms during the two day period, with NWS Warning polygons overlaid. The procedure allows one to monitor convective cloud top trends (BTs, features such as OTs and AACPs, texture) seamless during the day and night, while also observing lightning trends with the unobtrusive GLM flash points. From NWS HFO early on the 19th: “This mornings radar and satellite imagery shows scattered thunderstorms all across the state with the main impacts being damaging winds in excess of 60 mph.” And after the storms had passed late later on the 19th: “The vigorous cold front has finally moved east of the Big Island this evening as satellite imagery shows a line of strong thunderstorms moving eastward away from the Big Island.”
Hawaii is in the southwest corner of the PACUS sector, allowing for routine 5-min imagery to be collected. The Honolulu NWS forecast office requested GOES-West (1-min) mesoscale sector imagery during the event, allowing for storms to be analyzed in tremendous detail with little latency. Figure 4 provides 1-min sandwich imagery of thunderstorms crossing the big island late in the day on the 19th, which resulted in the issuance of two severe thunderstorm warnings. The imagery showed very active storm tops, including OTs and rapidly cooling BTs, and lightning activity as thunderstorms made landfall from the west.
Bill Line, NESDIS/STAR