A broad area of high pressure just east of the Hawaiian Islands will help maintain light, predominately southerly winds through early Friday. The weather pattern will change dramatically Friday night and over the weekend, as a frontal boundary advances through the state, bringing wetter and windier conditions to the islands. Periods of heavy rainfall, isolated thunderstorms, and strong winds will then persist through early next week. A drier air mass will move over the state around the middle of next week, however, isolated showers associated with the trade wind flow will persist.
Much of the state remains under the influence of a broad area of high pressure, maintaining stable weather and light southerly winds. These conditions are expected to persist through Friday morning. Despite the stable conditions, model guidance showcases a narrow band of moisture lifting northward into the state from the south, leading to isolated showers developing across Oahu later this morning. The highlight of this forecast however begins shortly thereafter, as the area of high pressure is projected to shift eastward toward the CONUS, opening the door for the next front. Model guidance continues to depict a steady moving frontal boundary advancing toward Niihau and Kauai by Friday afternoon, then proceeding through most of the islands throughout the weekend. This front will bring considerable amounts of moisture, with total PWAT normalized anomalies progged to be two to three standard deviations above average. Heavy rainfall and even some isolated thunderstorms will be on the docket for this weekend -- heavy enough that it may result in flooding potential for portions of the state.
As the aforementioned frontal boundary continues moving southward toward the middle of the state, it will begin to stall in the vicinity of Maui County. Additionally, moisture will pool from the south, enhancing rainfall potential and increasing chances for additional thunderstorms for the Hawaiian Islands, especially in windward areas. With the nearly stagnant pool of moisture and stalled out frontal boundary, the probability of rainfall training over these locations increases, and may incite intermittent flooding.
The flooding potential transitions into more of a wind threat late this weekend into early next week, as an area of high pressure builds north of the islands while the front dissipates. Strong trades will develop as a result of the strengthening pressure gradient, with some stabilization expected across portions of the island chain. Unsettled weather will continue, however, across windward and mauka areas, namely for the eastern half of the state, where lingering moisture from the washed out front remains. A substantially drier air mass is progged to advect into the islands by midweek, reducing shower coverage and focusing over primarily windward and mauka locales.
Expecting VFR conditions across most sites through the period. Southerly winds ahead of an approaching front will lead to light rain chances across mainly leeward Oahu from the early afternoon hours through Friday. MVFR conditions are possible under rain showers, primarily due to degraded cigs. Rain chances will be smaller across leeward Maui County, with dry conditions expected through the period for Kauai and the Big Island. Winds will shift from predominately land breezes to southerly during the daytime hours today, and are generally expected to persist as such into Friday.
No AIRMETs in effect.
A front approaching from the northwest will keep light to moderate south to southwest winds across the western waters and light to moderate southeasterly flow across the eastern waters through early Friday. The front will move through Kauai Friday afternoon, then shift southeastward into the central islands Friday night before stalling out in the vicinity of Maui County by Saturday. Moderate to fresh north shifting to northeast winds will build in behind the front, while lighter southeast flow prevails over the eastern end of the state. The front will gradually dissipate over the weekend as strong high pressure builds north of the state. This will allow trade winds to return and strengthen, reaching strong to near Gale force levels by late Sunday. The trades appear to strengthen further early next week, with near Gale to Gale force winds affecting much of the marine area.
The current northwest swell is on the downward trend, with buoy observations no longer supporting warning level surf. The downward trend will continue today, although surf along north and west facing shores should hold at advisory levels through much of the day. A High Surf Advisory is now in effect for most north and west facing shores through 6 pm HST. A Small Craft Advisory is in effect for most windward waters exposed to the swell through Noon HST. Surf should then drop below advisory levels through early Friday, before the next large northwest swell building down the island chain brings advisory level surf back to Kauai and Oahu Friday afternoon. This swell is expected to peak at warning levels Friday night and Saturday, before lowering below headline thresholds by late Saturday night. A series of small to moderate north and northwest swells will then move through Sunday through the middle of next week, with surf expected to remain well below advisory levels along north and west facing shores.
Surf along east facing shores will remain very small through Friday night. Surf is expected to rapidly build and become progressively more rough this weekend, with heights likely reaching advisory levels Sunday night or Monday and potentially exceeding warning levels Tuesday through late next week. Surf along south facing shores will remain small throughout the forecast period.
High Surf Advisory until noon HST today for Niihau-Kauai Leeward- Waianae Coast-Oahu North Shore-Maui Windward West-Kona-Kohala- Kauai North-Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.
Small Craft Advisory until noon HST today for Kauai Northwest Waters-Kauai Windward Waters-Oahu Windward Waters-Kaiwi Channel- Maui County Windward Waters-Big Island Windward Waters.
