The National Weather Service has posted a flash flood watch for Oahu, Kauai and Niihau through 8 a.m. today.
Forecasters said the threat of heavy rain will peak late Wednesday night and "drop quickly Thursday."
"A front northwest of Kauai continues moving toward the islands" forecasters said Wednesday afternoon. "South winds ahead of the front will carry warm, moist air over the islands. Meanwhile, a trough aloft will move over the area, bringing colder temperatures aloft and destabilizing the atmosphere. The moisture and instability will combine to produce a threat of heavy rain."
A flash flood watch means that conditions may develop that lead to flash flooding.
"Just because it’s not raining right now doesn’t mean you shouldn’t be prepared for the possibility of flooding," Robert Ballard, a meteorologist at the weather service’s Honolulu office, said Wednesday.
"If you live in a flood-prone area now is the time to get prepared in case flooding should materialize," Ballard said.
The front should move past Oahu today and the chance of rain will diminish, forecasters said. Trade winds are expected to return Friday into Saturday.