Beware the hours between 11 a.m. and 4 p.m. today, says the National Weather Service.
That’s when the greatest risk of flooding will occur with 2 to 4 inches of rain predicted.
With an unstable air mass and daytime heating, clouds may develop and bring heavy rain and a slight chance of thunderstorms for all the islands.
Today may be a repeat of Monday since the overall weather pattern is the same, said weather service lead forecaster Norman Hui.
A flood watch is in effect until 6 p.m. today for all islands.
Hui was reluctant to specify what portions of the islands would be affected.
"Everybody has an equal chance,” he said.
Hui conceded that with the light easterly wind prevailing, heavy rain might hit Leeward Oahu, the west side of Hawaii island and Central Maui. But, he added, “it could be anywhere.”
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On Monday, instability brought heavy rain, thunderstorms, funnel clouds and a possible water spout as well as hail on the west side of Oahu.
A severe thunderstorm warning was in effect for the island until 12:30 p.m., and a flash flood warning was canceled at 2:45 p.m.
Lifeguards reported a water spout off Tracks Beach in Nanakuli at about 12:40 p.m.
Flood advisories were posted for Hawaii island, Kauai, Maui, Molokai and Lanai and were canceled Monday afternoon.
At Honouliuli Stream a stream gauge showed rapid rises in water levels, and water topped the bridge near Old Fort Weaver and Weaver roads. Flooded roads were also reported in Waipahu and other communities in southwestern Oahu with six to eight inches of muddy water on some streets.
The weather service issues a watch when the risk of a hazardous weather or rainstorm has increased significantly but its occurrence, location or timing is still uncertain.
“People should have a plan of action in case a storm threatens, and they should listen for later information and possible warnings, especially when planning travel or outdoor activities,” the service advises.
Warnings are issued when hazardous weather or a rainstorm is occurring, imminent or likely and when weather conditions pose a threat to life or property.
