Photo Credit: Braden Jarvis

West Kaua’i

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South Kaua’i

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Kaua’i Mountains

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North Kaua’i

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East Kaua’i

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Detailed Forecast

Synopsis

A weakening cold front will stall near Maui today. Unstable conditions aloft will produce bands of showers and thunderstorms across the eastern half of the state through Friday. Drier and more stable conditions will develop over the western islands during this period. Another cold front and upper level disturbance moves into the region this weekend with increasing shower trends statewide from Saturday through Sunday. Expect periods of rain this weekend over all islands, heavy at times, along with isolated to scattered thunderstorms. Moderate to breezy trade winds will continue for most areas through the weekend.

Discussion

A combination of satellite and local radar imagery show a weakening cold front near Maui and the Big Island this morning. Bands of showers are developing mainly over the eastern Hawaiian Islands. A band of scattered thunderstorms has formed along a small scale convergence band just southeast of the Big Island. This band of thunderstorms lift northward through the Big Island southeastern coastal waters later today.
The weakening cold front will stall near East Maui and the Big Island today keeping wet weather conditions over the eastern half of the state in the forecast through Friday. Drier conditions are expected over the eastern islands from Kauai to Molokai during this time period with brief passing showers possible over windward and mountain areas in moderate to locally breezy trade winds.
Short to medium range model forecasts continue to show this front weakening into a trough and drifting slowly westward, spreading unstable showers and thunderstorms back over the western islands from Friday into Saturday. Another upper level trough also digs down into the Hawaii region creating unstable conditions as yet another cold front approaches the islands from the northwest. This next cold front will merge with the low level trough on Sunday near Kauai and Oahu producing deep convective showers across the state. Periods of heavy showers are expected to develop on Saturday and Sunday with strengthening trade winds. These breezy northeasterly trade winds may stack up showers along north and east slopes of each island, increasing the flash flooding threat due to terrain anchored heavy shower activity. Thunderstorms will also develop statewide as the eastward moving front, westward moving trough and upper level disturbance combine forces.
Long range weather models continue to show divergent solutions early next week from Monday onward. The American (GFS) model shows a deep cut off low developing north of Kauai and then moving south over the islands in an unstable weather pattern. The European (ECMWF) model now shows a similar cut off low pattern as compared to the GFS. Both the GFS and ECMWF models remain highly inconsistent from run to run during this time period significantly reducing our confidence in all weather elements from Monday onward. Current grids show a moderate wet trade wind pattern. However, this forecast will likely change as the time period grows shorter and weather model guidance improves. Stay tuned for updates to the Hawaiian Island weather forecast for early next week as significant changes will occur and island by island weather impacts will evolve over time.

Aviation

The cold front has cleared Oahu where showers have come to an end, but breezy trades are still focusing MVFR ceilings along the terrain. The front will stall in the vicinity of Maui today where moderate northerlies will focus a steady dose of low clouds and showers over windward slopes with frequent MVFR and pockets of IFR expected. Meanwhile, isolated thunderstorms will be possible in the general vicinity of the Big Island, particularly along the eastern slopes and adjacent waters where the greatest instability resides.
AIRMET Tango for moderate upper turbulence remains in effect for the entire area. In addition, SIGMET Yankee has been issued for severe upper turbulence FL250/FL400 southwest of the islands. This band of severe turb will expand northeastward into areas near and east of Oahu by late morning, including Maui County and the Big Island.
AIRMET Sierra remains in effect through this morning for N slopes of Oahu. AIRMET Sierra will likely remain in effect for Maui County for the balance of the forecast period.

Marine

A front over the southeast waters will drift east today, producing periods of showers and isolated thunderstorms across the state. Moderate to locally strong northeast winds will follow behind the front as a high builds far northwest of the area. Over the weekend a slightly stronger high will build northwest of the state, and a trough over or near the state will sharpen the gradient, strengthening northeast trades to fresh to strong area wide. A Small Craft Advisory (SCA) is currently in effect due to the combination of high seas due to an XL northwest swell and locally strong winds for most zones through Thursday afternoon. The SCA may need to be extended for some zones as seas fade but locally strong winds shift eastward.
A long period XL northwest swell (300-320 degree) will gradually fade over the rest of the week. A High Surf Warning (HSW) remains in effect along exposed north and west facing shores for the smaller islands and for Big Island west facing shores through today. As this northwest swell continues to fade and new moderate north swell will fill in Friday that will keep surf elevated, especially along north facing shores. A new extra long period moderate northwest swell (310 degree) is expected to boost surf heights back to High Surf Advisory (HSA) levels along north and west facing shores Sunday into Monday. Surf along east facing shores will remain small and choppy due to the combination of tradewind swell and wrap from the north to northwest swells through early next week. Elsewhere, small surf remains in the forecast for south and east facing shores into early next week.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST this evening for north and west facing shores of Niihau, Kauai, Oahu, Molokai, north facing shores of Maui, and west facing shores of the Big Island.
Small Craft Advisory until 6 PM HST this evening for most Hawaiian waters and channels.

Data Courtesy of NOAA.gov