Oahu and Maui County are under a flash flood advisory this evening as scattered heavy rain falls throughout the islands.

The National Weather Service said the advisory lasts until 6:45 for Oahu and 8:15 for Maui County.

Forecasters said earlier today that unstable weather over the islands could cause heavy rain and possibly thunderstorms this afternoon and evening.

“We already have thunderstorms on the Big Island that developed late this morning,” said John Bravender, a forecaster with the National Weather Service. He said heat rising through the moist, unstable air over the islands could cause rain clouds to develop this afternoon and evening and the rain may be heavy.

The unstable conditions are expected to continue through tomorrow evening.

Rain, snow and hail fell on Big Island summits, Bravender said. A winter weather advisory is in effect until tomorrow afternoon on the slopes of Mauna Kea and Mauna Loa.

“We could see a repeat of what we see this afternoon, tomorrow,” Bravender said.

Tradewinds should return Wednesday. But the forecast for this weekend calls for more unstable weather and the chance of heavy rain and thunderstorms in the afternoon.