People going to outdoor graduation ceremonies and Memorial Day services should bring a fan and an umbrella because of hot, muggy weather and the chance of rain.

Heavy rain was falling over parts of Kauai Friday morning. The county closed the Kekaha landfill because of lightning strikes.

Forecasters said the threat of heavy rain and thunderstorms near Kauai is likely to spread to Oahu by Saturday.

The greatest chance of rain is over interior and mauka sections of Kauai and Oahu.

The National Weather Service says the humid conditions combined with daytime heat and a weather system near Kauai could cause heavy rain and even thunderstorms to develop through the holiday weekend.

"Light winds and humid conditions will prevail into the weekend," forecasters said.

The forecast calls for a 50 percent chance of rain over southern Oahu from Hawaii Kai to Kapolei through Sunday.

National Weather Service meteorologist Derek Wroe said it’s difficult to predict where and when showers will develop.

"These showers are going to pop up. They’re going to be scattered here and there. It should be a brief downpour and it should go away," Wroe said. "But anything that does pop up will be heavy."

Wroe said residents should be aware of the possibility of lightning if thunderstorms develop.

"People should be aware that even if the conditions start out nice where you are, a heavy shower could pop up, even a thunderstorm," Wroe said.

Skies over Kauai will be cloudy Friday night during the peak of the Camelopardalids meteor shower between 8 and 9 p.m. Oahu may see partially clearing skies and less cloudy conditions over Maui and the Big Island.

Tradewinds are predicted to return on Monday, but the atmosphere will still be unstable and moist so windward and mauka showers that could move over leeward sections of the islands are likely.