NOTE: This story has been updated to include the audio message issued by Hawaiʻi County Civil Defense on Friday afternoon.

(BIVN) – The National Weather Service in Honolulu has issued a Flash Flood Watch for the entire Big Island through Saturday afternoon.

A Flash Flood Watch means that conditions are favorable for flash flooding. “An approaching upper level disturbance will further destabilize the air mass, with abundant low-level moisture already in place,” forecasters wrote. “Slow-moving and persistent heavy showers and thunderstorms will bring the threat of flash flooding.”

“Heavy rainfall could result in low spots in roads becoming dangerous and impassible due to severe runoff,” the National Weather Service said. “Debris in streams and gulches could clog bridges and culverts resulting in dangerous flooding. Isolated landslides could also occur.”

A High Surf Advisory will also be in effect for south facing shores of all islands from 6 p.m. this evening to 6 p.m. Monday.

“A powerful storm in the southern hemisphere generated a long-period south swell will begin to arrive today, and then peak over the weekend,” the National Weather Service said. “The swell will remain elevated through Monday, then gradually diminish.”

Surf heights will increase to 8 to 12 feet, with locally higher sets possible.

“Beachgoers, swimmers, and surfers should heed all advice given by ocean safety officials and exercise caution. Know your limits and seek ocean recreation areas best suited for your abilities. Boaters should expect recreational surfers and body boarders utilizing harbor channels to access surfing areas,” forecasters warn.