(BIVN) – Two low pressure systems will bring potentially heavy rain to the Hawaiian islands in the coming week.
In a “Hydrologic Outlook” message posted by the National Weather Service on Saturday afternoon, forecasters said “the duration and intensity of rainfall will bring the potential for flooding impacts as early as Tuesday for Kauai, and Wednesday onward for the remainder of the area.”
Significant snowfall is also in the forecast for the summits of Maunakea and Mauna Loa on the island of Hawaiʻi.
The National Weather Service said it is “too soon to forecast rainfall amounts or where the heaviest rain may fall, but leeward areas are as likely to experience heavy rainfall as windward areas.”
From the NWS forecast discussion posted at 8:57 p.m. HST:
Medium range forecast guidance continues to show this kona low drifting eastward towards Kauai from Sunday to Tuesday. Shower activity increases over the western half of the state for Kauai by late Monday through Tuesday and for Oahu by Tuesday morning. Heavy rain and thunderstorms remain in the forecast for this first round with rainfall impacts mainly over Kauai County and Oahu.
Another kona low drops in from the northwest on Tuesday and sets up just west of Kauai by Wednesday. This second low is stronger than the first one with deeper southerly winds that will draw up deep tropical moisture into the eastern half of the state. This unstable tropical moisture will spread periods of showers and thunderstorms across all islands from Wednesday into next weekend.
These cold core lows can produce significant amounts of rainfall in a very short time period. Flooding threats are elevated statewide as these two kona lows take aim on the islands. The heaviest rain areas typical occur under the strongest wind divergence aloft and we will have to wait until the forecast time period gets closer to identify where these areas might set up. Periods of wet weather with locally heavy rain and thunderstorms should be expected for all islands next week. Pay close attention the the weather forecast updates over the next few days as island by island impacts will evolve as the model guidance improves over time.
The National Weather Service says that over the next 24 to 48 hours, the agency will consider the possibility of issuing a Flash Flood Watch, at least for the western islands on Monday and Tuesday.