NWS warns heavy rain, flash flooding for Big Island late Monday

The National Weather Service on Saturday issued a Hydrologic Outlook warning that heavy rain and flash flooding are possible from late Monday into next weekend, and island officials urged preparedness for impacts on Hawaii Island communities. The outlook notes a large low pressure system developing northwest of the state that will pull a very moist southern air mass northward across the islands.

The Hydrologic Outlook, filed at 3:24 PM HST Sat Mar 7 2026, carried the product header string HIZ001-003-004-006-007-009>011-015>018-022-023-026>054-081530- and included the line: "HEAVY RAIN AND FLASH FLOODING POSSIBLE FROM LATE MONDAY INTO NEXT WEEKEND..." The product singled out Kauai County for initial increased flooding probabilities "late Monday into Monday night" and said "The flooding threat will likely expand eastward and envelope the entire state from Tuesday into the later part of next week." The Hydrologic Outlook also stated in the excerpt provided, "The flooding potential may persist into next weekend or early the following week," and the text included the truncated sentence, "It is too early to ..." reflecting remaining uncertainty in the product excerpt.

Local reporting and county officials have already moved to alert residents. The Hawaii Tribune-Herald said the National Weather Service issued a statewide flood watch "running from late today through Monday afternoon" and described the developing system as "a kona low – a powerful low-pressure system that can produce strong winds and heavy rain – expected to develop north of Kaua‘i today and push moist, unstable air across the state from the south and southeast." The Tribune-Herald also relayed NWS language that "On the Big Island and Maui, the greatest flood risk will be on southeast slopes."

Hawaii County leaders emphasized rapid changes in the threat area. Mayor Kimo Alameda said, "Storms like this are unpredictable and potentially dangerous, so we urge the public to be prepared," and warned, "The picture right now looks like the biggest risk is to Puna and Hilo communities, but that could shift to Ka‘u or to Kona coast communities by later this weekend." Civil Defense administrator Talmadge Magno added, "This is an evolving storm, so we encourage everyone to stay informed about the forecast," and urged residents, "If you haven’t already done so, we encourage you to sign up for emergency alerts at the Hawaii County Civil Defense website to receive updates on your cell phone."

Preparedness guidance in the Tribune-Herald excerpt includes concrete steps: "Consider changing or delaying plans for travel or outdoor activities during inclement weather, including routes that have low-lying areas prone to flooding," and "Know the areas that are prone to flooding, especially near your home, and use extra caution around them. Heavy rain uphill from your location can cause flooding, even if it’s not raining where you are."

Local forecast detail for Big Island North reflects the heightened risk window: the zone area forecast lists "Scattered Showers then Heavy Rain," with Wednesday showing "Scattered showers, then periods of rain and possibly a thunderstorm after noon. Some of the storms could produce heavy rainfall. High near 62," and Wednesday night calling for "Scattered showers. Cloudy, with a low around 52 to 53, South southeast wind 5 to 8 mph becoming calm after midnight."

Big Island Video News published a summary of the Hydrologic Outlook on March 7. With the NWS product indicating the flooding threat could expand statewide from Tuesday and possibly persist into the following weekend, county and emergency officials say residents in Puna, Hilo, Ka‘u and Kona communities should monitor updates from NWS Honolulu and Hawaii County Civil Defense as conditions evolve.