A Kona Low established itself west of Kauai on 16 Mar 2020, driving anomalously high levels of tropical moisture (TPW of 1.5″ to 2.0″) into the region. GOES-West full disk water vapor imagery showed the tightly wrapped low set up west of the Hawaiian Islands and only slowly moving east from late on the 15th through the 16th (Fig 1).
The Advected Layer PW product combines temperature and moisture information from multiple polar-orbiting satellites to provide a 4D structure of moisture in the atmosphere. In this case, the blended product shows deep moisture from the tropics wrapping around the low and over Hawaii in all layers (Fig 2).
The increased moisture and forcing associated with the low resulted in the development of persistent showers thunderstorms over/near the islands during the previous evening through the day. These storms produced heavy rain and gusty winds, leading to the issuance of a Flash Flood Watch for the state, a Flash Flood Warning for the island of Kauai, and multiple Special Marine Warnings for gusty winds.
The development and evolution of deep convection near the islands around the sunrise period is shown in an IR to VIS/IR Sandwich transition loop (Fig 3). Prior to sunrise, the animation shows IR alone, while after sunrise, the animation includes the high texture of the VIS in combination with the IR. The most impressive convection is diagnosed developing near and northeast of Kauai.
Visible imagery combined with semi-transparent GLM after sunrise reveals periodic lightning flashes associated with the convection, but with relatively low density (Fig 4). Surface obs indicated measured peak wind gusts of 38 knots associated with these thunderstorms. Hawaii is in the southwest corner of the GOES-West PACUS sector, meaning 5-min imagery is always available over the islands.
Substituting visible imagery for the Day Cloud Phase Distinction RGB provides more insight into cloud makeup with this event (Fig 5). It provides a contrast between low liquid clouds (cyan) and high ice clouds (red and yellow), with convective cores (textured red/yellow) still apparent due to the contribution of texture from the 500 m VIS.
The Kona Low remained in place west of Hawaii on the 17th, continuing to drive moisture northward and resulting in persistant thunderstorm activity over and near the state. Given the continued thunderstorm flash flood threat, WFO Honolulu requested and was granted a long-duration (36 hours) GOES-West meso sector (2) to provide 1-min satellite imagery over the region. Ninety-minutes of 1-minute visible imagery from the morning of the 17th, with semi-transparent GLM FED overlay, shows the most robust thunderstorm activity developing south of the islands (Fig 6). The very high temporal resolution imagery with very low latency provides forecasters a valuable tool for diagnosing newly developing updrafts and tracking their evolution, particularly over the ocean far from radar coverage.
The Kona Low stuck around west of Hawaii through Thursday night, when it finally lifted to the northeast and exited the region as a broad upper trough/closed low approached from the west. Hourly GOES-West Water Vapor imagery from Sunday morning thorough Friday morning shows the evolution of the upper low and associated lightning activity (GLM FED) through the week (Fig 7). The continued flux of tropical moisture and development of convection near/over Hawaii is apparent in the imagery. As the late week trough approaches from the west, the Kona low lifts northeast within the increasing southwesterly flow.
Bill Line, NESDIS and CIRA
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