Heavy rains and thunderstorms could produce flood conditions across the state Sunday and Monday as the remnants of former Tropical Storm Howard continues to move eastward over the state.

A flash flood warning is in effect for all islands through Monday afternoon.

Forecasters predict abundant moisture from Howard and instability caused by an upper-level trough moving southward over the state will combine to create ideal conditions for locally heavy showers. That in turn could result in flash floods as rainfall hits grounds still saturated from heavy rains associated with former Tropical Storm Darby, which passed over the state two weeks ago.

According to the National Weather Service, the northern end of the state is most likely to experience flash flooding.

Surf is also on the rise because of an east swell generated when Howard was still a tropical storm. Wave heights of 6 to 9 feet are expected on east shores through tonight and the swell could continue through Sunday.

A high surf advisory is in effect through 6 a.m. Sunday, but could be extended.

As the center of Howard moves near or over Oahu Sunday, winds will shift and become light and southerly.

Derek Wroe, a meteorologist with the Honolulu office of the National Weather Service, said the heavy showers Sunday into Monday could be spotty, with some areas getting heavy rain, while other parts of the island may see only a few showers.

Kauai and Oahu caught the brunt of Howard’s initial crossing over the state. Rainfall highs were recorded at Mt. Waialeale (3.65 inches) and Kilohana (1.95) on Kauai and Lyon Arboretum (2.02) and Moanalua (1.63) on Oahu over the 24-hour period ending 7:45 p.m. on Saturday.

An accidental discharge resulted in nearly 13,000 gallons of wastewater flowing into a storm drain that leads to the Ala Wai Canal on Saturday morning.

The Department of Health posted warning signs and advised the public to stay out of the water until the signs were removed.

The discharge resulted in the cancellation of the second day of the Ala Moana Bowls bodyboard competition. The event will not be rescheduled.

Forecasters are also watching Tropical Storm Ivette, approaching the islands from the west.

Ivette is expected to weaken into a remnant low as it nears Hawaii.

Tropical Storm Ivette is weakening as it turned northwest over cooler waters and wind shear tears it apart.

It still remains on track, however, for whatever is left of the storm to bring humid conditions and rain to the state as early as Wednesday.

At 5 p.m. on Saturday, Ivette had sustained winds of 45 mph and was moving west-northwest at 12 mph, about 1,245 miles east of Hilo.

National Hurricane Center forecasters are also watching an area of thunderstorms off the southwestern coast of Mexico that has an 80 percent chance of becoming a tropical cyclone this weekend.

If it intensifies into a named storm, it will be called Javier.