An unstable weather pattern will likely bring continued heavy showers across the state through Saturday night, according to the National Weather Service.
A flash-flood watch is in effect for all islands through 6 a.m. Sunday as strong low winds combine with a surface trough to produce slow-moving heavy rain and thunderstorms. NWS forecasters warn that while heavy rain is not expected to be widespread, intense localized rain is likely and could lead to flash flooding in streams and urban areas.
The unstable conditions prompted the weather service to issue a special weather statement late Friday afternoon, warning the public of the possibility of severe thunderstorms producing damaging wind, hail the size of quarters, frequent lightning, intense rainfall and possible funnel clouds. The statement advised preparation for rapid changes in the weather.
The heavy rain began around midday Friday. Between 11 a.m. and 2 p.m., more than an inch of rain fell on Nuuanu, Manoa and Maunawili on Oahu. The Kahakuloa and Pukalani areas of Maui also experienced heavy rainfall during the same period.
Around 5:25 p.m. weather service radar detected nearly stationary heavy rain near Kawela on Molokai. Less than an hour later, stationary heavy rain was also reported near Hamoa and Hana on Maui, prompting a flood advisory.
The advisory was upgraded to a flash-flood warning a half-hour later as the heavy rain continued. Forecasters warned of possible rockfalls and mudslides resulting from storm runoff. The public was advised to stay away from streams, drainage ditches and low-lying areas prone to flooding, and to be aware that rainfall and runoff could cause hazardous driving conditions due to ponding.
The weather service noted that areas can be vulnerable to flash flooding even if heavy rain is not present in the immediate vicinity. Officials advised monitoring the latest forecasts and being prepared to take immediate action if further flash-flood warnings are issued.
Winds are expected to be light Saturday, with the possibility of locally gusty wind near thunderstorms.
A high-pressure system is expected to build to the north of the current upper-level low during the early part of the coming week, resulting in a return of tradewinds. The high-pressure system will bring clouds and passing showers to windward and mauka areas.
