A flash flood watch has been issued for Oahu, Kauai and Niihau from Wednesday night through Thursday night.

The National Weather Service reports that a deep upper level trough will slowly approach from the northwest during the next few days.

“The atmosphere will gradually moisten tonight and Wednesday across the western end of the island chain, and by Wednesday night, the threat of heavy showers will increase, especially near Kauai,” weather officials said.

Light trade winds will produce the highest chances for rainfall along windward slopes, though heavy showers could develop anywhere from Kauai to Oahu. These conditions may continue into Friday.