West Kaua’i

Tonight: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 83 to 88 near the shore to around 74 above 3000 feet. Light winds. Chance of rain 50 percent.

Tuesday Night: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to around 63 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 69 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 78 to 87. East winds around 10 mph. Chance of rain 40 percent.

Tuesday Night: Mostly clear. Isolated showers in the evening. Lows 69 to 76. Northeast winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows around 68 in the valleys to around 60 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 74 to 82 in the valleys to around 67 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 68 in the valleys to around 60 above 4000 feet. Light winds. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 64 to 74. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny with scattered showers. Highs 70 to 85. East winds around 10 mph. Chance of rain 50 percent.

Tuesday Night: Mostly clear. Isolated showers in the evening. Lows 64 to 74. East winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 65 to 76. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 85. East winds around 10 mph. Chance of rain 40 percent.

Tuesday Night: Mostly clear with isolated showers. Lows 65 to 75. Northeast winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trades will continue to bring isolated to scattered showers to windward and mauka areas through this evening. Winds will begin to ease tonight, then turn out of the south by midweek as an area of low pressure develops to the north of the state. Rain chances and the potential for heavy rain will increase during the second half of the week.

Discussion

Current radar and satellite imagery show isolated to scattered showers moving into windward and mauka areas of the state on the moderate to locally breezy trades this afternoon, along with clouds and showers developing along the kona slopes of the Big Island from Kailua-Kona to South Point and up to Volcano due to daytime heating.
The high driving our trades to the northeast of the state will weaken and shift further northeast as deep troughing develops across the region north of the state over the next couple of days. This will weaken the trade wind flow late tonight into Tuesday, allowing for a hybrid lighter trade wind and land/sea breeze pattern to develop with limited showers favoring windward and mauka areas overnight, then daytime heating will induce clouds and a few showers over leeward areas Tuesday afternoon.
Model guidance continues to indicate that the trough to the north will deepen and form a broad cutoff low both aloft and at the surface by late Wednesday into Thursday, causing the low level flow to veer out of the south across the state. With the increasing instability due to the nearby low and deep tropical moisture being advected northward in the southerly flow, the potential for heavy rain will increase beginning Wednesday and persist through at least Friday. In this flow, the heavy showers will likely favor south-facing portions of each island.
Beyond Friday, forecast confidence decreases significantly as the global deterministic model solutions diverge. However, the ensembles lean toward bringing trades back on Saturday into Sunday, so have nudged the forecast in that direction for now.

Aviation

Moderate to locally breezy trade winds continue through this evening before weakening tomorrow due to a nearby surface trough. This will cause a hybrid light trade wind and sea breeze pattern tomorrow. Terrain sheltered areas will be more likely to see afternoon cloud and shower development as a result. Brief and isolated shower activity is expected over windward and mountain areas. MVFR conditions will occur within showers, while VFR prevails elsewhere.
AIRMET Sierra is in effect for mountain obscurations for portions of the Big Island due to windward showers and afternoon clouds and showers over the Kona slopes. Conditions over the Big Island should generally improve by early tomorrow morning. Other windward areas could see mountain obscurations tonight due to upstream isolated to scattered showers, but conditions will be borderline.
AIRMET Tango will remain in effect for moderate turbulence downwind of island terrain through this evening, but is expected to end afterwards due to lighter winds tomorrow.

Marine

High pressure centered far northeast of Hawaii will drive moderate to fresh trade winds tonight. Winds are in the process of weakening as a low pressure system dig southward towards the state, therefore, the Small Craft Advisory has been cancelled for all waters and should remain so through the rest of the week. The low will stall north of the islands and draw moisture out of the tropics and over the area through the second half of the week, so expect an increase in showers.
A long-period south swell will increase to slightly above seasonal averages through Wednesday. Surf is then forecast to drop to near or slightly below average for the rest of the week, maintained by a mix of new, small south swells.
A long-period northwest swell will arrive on Tuesday that will continue through the end of the week even as swell energy becomes shorter period as it is reinforced by a low to the north- northwest of the Hawaiian Islands. Surf along east facing shores will diminish tonight through the rest of the week as winds weaken.
A small, long-period west swell originating from Typhoon Choi-wan is forecast to reach the islands Thursday into the weekend, which may produce moderate surf for west-facing shores.

Fire weather

Moderate to locally breezy trades will gradually ease overnight into Tuesday with RH values just above the critical threshold for fire weather during the afternoon hours. Fire weather risk then diminishes through the remainder of the week as moisture increases, winds decrease, and showers increase in coverage. The inversion should range from 6 kft to 8 kft through Tuesday.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov