A cold low-pressure system in the middle atmosphere could bring heavy rain and thunderstorms to the northwestern areas of the state today, according to the National Weather Service.
A flash flood watch remains in effect for Kauai, Niihau and Oahu through 6 p.m. as the system destabilizes the atmosphere.
The weather service warns that more than 2 inches of rain an hour could lead to flash flooding.
Heavy rain saturated areas of Oahu and Kauai on Monday, making flooding more likely should heavy showers continue today.
The weather service is advising the public to be aware of conditions that could lead to flash flooding and to remember that it does not have to be raining heavily in the immediate area for flash flooding to occur.
At 3:19 p.m. Monday radar detected stationary heavy rain near Waianae as well as heavy rain developing near Pearl Harbor, Waipahu, central areas of the Koolaus and Windward Oahu.
Over the 24-hour period ending 8:45 p.m. Monday, more than 4.5 inches of rain fell over Mount Waialeale on Kauai. Elsewhere on Kauai, 3.8 inches of rain was recorded in North Wailua Ditch and 2.25 inches in Kapahi.
During the same period, more than 5 inches of rain fell on Poamoho on Oahu. Significant amounts of rain fell at Kamananui Stream (2.17 inches), Lualualei (1.6 inches), Palehua (1.3 inches) and Waianae Boat Harbor (1.2 inches).
Heavy showers near Kahaluu on Monday evening prompted a flood advisory through 12:15 a.m. today.
The rainy weather could extend through midweek as light winds and muggy conditions contribute to buildups in the afternoon.
Tradewinds are not expected to return until the weekend.
