Sunday will be a good time to get out your umbrella as weather conditions are expected to go downhill, with scattered showers and a chance of heavy downpours and perhaps even a few thunderstorms as the day goes along.
A surface trough will be moving across the state from east to west, starting with the Big Island Sunday morning and lasting through Monday. The trough will increase clouds and the chance of showers, while a nearby upper level low pressure system will bring unstable conditions and the chance of locally heavy showers. All of that will depend on just how close the upper low comes to the state; the closer it is, the higher the chance for localized downpours and thunderstorms.
If you're driving, be on the alert for those downpours, which will drastically reduce visibility and cause roadway ponding later Sunday and Monday. Also, there is the possibility of cloud-to-ground lightning strikes. If you are close enough to hear the rumble of thunder, you are close enough to be hit by lightning. Stay indoors.
Hikers should be aware that streams may run high later Sunday and Monday, which could cut off hiking trails. It doesn't have to be raining where you are for a stream to rise rapidly. Choose another day when the weather is better.
Trade winds will be increasing as the trough and upper low pass, with the possibility of some gusty conditions on Monday. There will be enough instability and moisture to maintain a rather wet trade wind pattern through much of the coming week.
At the beach, a High Surf Advisory remains in effect for south facing shores until 6 p.m. Monday. Surf will decline through Monday afternoon as another south reinforcement is expected, peaking Tuesday and Tuesday night. Increasing trades will also bring a choppy east swell.