Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Haze in the morning. Mostly sunny with isolated showers in the morning, then cloudy with scattered showers in the afternoon. Highs 77 to 84 near the shore to around 70 above 3000 feet. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Cloudy. Showers in the evening, then numerous showers after midnight. Lows around 65 near the shore to around 56 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 90 percent.

Monday: Partly sunny with scattered showers. Highs 75 to 84 near the shore to around 68 above 3000 feet. North winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Haze in the morning. Partly sunny with scattered showers in the morning, then cloudy with numerous showers in the afternoon. Highs 76 to 83. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy and breezy. Showers in the evening, then numerous showers after midnight. Lows around 66. Northeast winds 15 to 20 mph. Chance of rain 80 percent.

Monday: Partly sunny with scattered showers. Highs 75 to 83. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Haze in the morning. Partly sunny with scattered showers in the morning, then cloudy with showers in the afternoon. Highs 68 to 75 in the valleys to around 61 above 4000 feet. Light winds becoming northeast up to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy with showers. Lows 57 to 66 in the valleys to around 55 above 4000 feet. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 90 percent.

Monday: Mostly cloudy with numerous showers. Highs 67 to 74 in the valleys to around 59 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 60 percent.

North Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with showers in the afternoon. Highs 70 to 79. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 90 percent.

Tonight: Breezy. Cloudy with showers. Lows 60 to 67. Northeast winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 90 percent.

Monday: Mostly cloudy with numerous showers. Highs 68 to 78. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 60 percent.

East Kaua’i

Today: Haze in the morning. Partly sunny with scattered showers in the morning, then cloudy with showers in the afternoon. Highs 69 to 81. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy with showers. Lows 59 to 70. North winds 10 to 15 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 67 to 80. North winds 10 to 15 mph. Chance of rain 60 percent.

Detailed Forecast

Synopsis

A weak trough over Maui County this morning will continue to slowly drift northward as a shallow cold front approaches the islands from the northwest. These two systems will merge near Kauai and Niihau by tonight, producing widespread showers over the Garden Isle. Breezy and cool northerly winds will fill in behind the front as it moves down the island chain, stalling out near the Big Island by Tuesday. Showers will favor windward areas and all areas within the passing frontal cloud band. A very wet weather pattern unfolds from Wednesday night through Friday morning with unstable southerly kona winds bringing potential for heavy rain, with strong gusty winds, and strong thunderstorm threats. This fast moving kona low weather pattern may produce statewide severe weather threats during this time period.

Discussion

Satellite imagery this morning shows a few thunderstorms developing in the coastal waters just west of the Big Island along the leeward wind convergence plume. These thunderstorms will likely diminish later this morning. Farther northwest of the state a cold front continues to approach the island chain.
For today, expect light to moderate trade winds to continue for most areas with some shower activity mainly favoring the windward and mountain areas. Wetter trends are expected by tonight as a cold front combines forces with the weak low level trough near Kauai lasting into Monday. Expect widespread showers developing across the Garden Isle lasting into Monday morning. Breezy and cool northerly winds will quickly move in with decreasing shower trends after this front passes through each island. The arrival timing of the showers are set to reach Oahu and all the islands in Maui County by Monday morning, then spread to the Big Island by Monday afternoon. The cold front will weaken as it passes through each island. Showers along the frontal band will be more numerous near Kauai with lesser amounts of rainfall expected to reach the eastern islands with this event. Thunderstorms may develop just north of the island chain along the passing frontal boundary. The front will stall out and diminish near the Big Island by Wednesday with a brief period of decreasing shower trends in the forecast.
By Wednesday night the weather conditions are trending towards a significantly wetter and unstable pattern, as a kona low weather system moves through the Hawaii region from Wednesday night through Friday morning. Southerly to southwesterly kona winds will pull up unstable tropical moisture northward into two passing cold core lows. Severe weather threats are increasing with this system as the latest models are improving their consistency during this time period. Threats appear to be statewide from a 12 to 24 hour time period for each island, with rising threats for heavy rain with storm total rainfall amounts in the 1 to 2 inch range, locally higher rainfall totals are possible, some snowfall and warning level winds are forecast over the Big Island Summits, strong gusty downsloping winds will likely impact some communities along northeast facing mountain slopes, and last but not least the growing potential for severe thunderstorm activity.
A blended model approach was used for this forecast to reduce run to run limitations in any one weather forecast model. Forecast rainfall projections for this event were increased using the 75 percentile of the National Blended Model, which has only a 25% chance of exceedance. Isolated to scattered thunderstorms and heavy rainfall threats have expanded statewide. Stay tuned for the latest weather forecast updates with this kona low weather system as the island by island impacts and severe weather threats will likely evolve over time.

Aviation

Moderate trades expected. SHRA and low cigs focused over windward and mauka locations with some limited spillover to leeward areas. A low level trough over the islands and a new trough moving in will combine to increase the potential for increased SHRA and low cigs by this afternoon into the evening especially over the western end of the state. MVFR conds can be expected in SHRA but otherwise VFR should prevail.
No AIRMETs currently in effect however with increased potential for rain over the western end of the state AIRMET Sierra for mtn obsc may be needed at various times through the rest of the weekend.

Marine

Light to moderate northeast to east winds will continue through much of the day, as a weak surface ridge remains north of the state. Pockets of fresh breezes are possible over the typically windier waters and channels from Maui County to the Big Island during this time. Fresh to strong northerly breezes are expected over the western end of the state from early this evening through Tuesday, as a front moves down the island chain. A Small Craft Advisory will be issued later today for the potential of strong northerly winds and rough seas over the waters surrounding Oahu and Kauai. Uncertainty increases from around midweek onward, with some models depicting low pressure forming along the stalled frontal boundary in the area.
With a blocking high persisting over the northwest Pacific, the primary swell source will remain predominantly from the north throughout the week. This will feature a mix of rough, short- period wind waves from the strong northerly winds expected locally early in the week, along with medium-period northerly swells. Guidance remains in good agreement, indicating an upward trend from Tuesday through late in the week due to the potential for a gale- to storm-force low forming well to the north. Surf heights could approach or reach the advisory level for north facing shores Wednesday through Friday if this scenario materializes.
Surf along east-facing shores, not exposed to northerly swells, will remain small each day due to the lack of local trades and upstream swells.
Surf along south-facing shores will remain around the seasonal average through midweek, with a mix of short-period southeast swells and occasional background south swells. Uncertainty increases late in the week, with the potential for southerly winds to evolve, which could translate to a brief period of rough, short-period surf.

Fire weather

Wind speeds will remain below critical fire weather thresholds through the middle of next week. Moisture levels rise swiftly from Thursday onward with southerly winds bringing another round of widespread rainfall in the forecast for all islands.

HFO Watches/Warnings/Advisories

None.

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