Keep umbrellas handy through Mother’s Day as rainy weather is expected to persist.

“It’s not going to be a sunny weekend,” said Tim Craig, a forecaster with the National Weather Service. “We’re looking for more clouds and rain, some of it heavy, through the weekend and possibly even through most of next week.”

Mother’s Day could be humid as well as rainy. Craig said tradewinds will shift to Kona winds on Sunday, bringing muggy conditions.

Blame it on cold, unstable air in the upper atmosphere, a weather condition similar to the system that brought lightning and thunderstorms to the islands earlier in week.

The cold, moist and unstable air is creating “enhanced” tradewind showers that are heavier than normal and breezy tradewinds are blowing the normal windward and mauka showers into leeward areas, forecasters said.

That’s what led the weather service to issue a flood advisory early this morning for Oahu and Maui. Rain gauges showed nearly 4 inches of rain fell at Kukui in Upcountry Maui and a little more than 3 inches in Kaupo Gap, Maui, during the 24-hour period ending at 8 a.m. The flood advisories expired by 8 a.m.

On Oahu, 2.7 inches fell in the Oahu Forest Reserve in the northern end of the Koolau Mountain; 2.4 inches was recorded in Palisades; 2.1 inches fell Kahana and 1.9 inches fell in the back of Manoa Valley.  

The weather service also issued a winter weather advisory for summits of the Big Island because cold temperatures in the upper atmosphere are creating freezing rain and snow.

Rain and the possibility of thunderstorms remain in the forecast for the rest of today and tonight.

Kevin Kodama, a hydrologist with the weather service, said it’s unusual, but not unprecedented to see so much rain in May.

“The wet season typically runs through April, but it’s not a hard boundary,” Kodama said. “Just because you hit April 30, doesn’t mean the tap turns off.”