A flash flood watch for Kauai, Niihau and Oahu is in effect from this evening through Wednesday afternoon.
The National Weather Service said moisture and instability from a low northwest of the area are expected to produce flooding rain, affecting areas that do not usually flood, and causing low spots in the road to become dangerous and impassable due to severe runoff. The flash flood watch is scheduled to go into effect at 6 p.m. and run through 4 p.m. Wednesday.
Forecasters said an out-of-season upper low and surface front positioned to the west-northwest is causing a wet pattern to unfold across the western end of the state.
Scattered showers are expected today, along with possible thunderstorms over Kauai and Oahu tonight through Wednesday. In addition to the wet pattern, the light winds combined with dewpoints lingering in the low 70s will keep humid conditions in place.
The heat index, a reflection of what it feels like when air temperature and relative humidity are combined, is expected to reach 94 in Honolulu early this afternoon, and 95 in Kapolei and Kahului.
Forecasters expect the warn and muggy conditions, with increasing chances of rain, to remain through Tuesday as this upper low begins to drift toward the islands. The threat of heavy rain may also shift eastward down the island chain by the middle of the week.
Trades will remain light out of the southeast, and a more typical trade wind pattern, along with a drying trend, is not anticipated until late Thursday.
More records, meanwhile, were set over the weekend.
On Saturday, record high temperatures were set at Kahului, at 93 degrees, breaking an old record of 91 in 1980, and 87 in Lihue, tying with the record set in 1981.
On Sunday, a record daily maximum rainfall of 0.54 inches was set at Lihue, breaking the old record of 0.40 inches set in 1978. A record high of 94 degrees Fahrenheit was set at Kahului, breaking the old record of 90 set in 1980.