West Kaua’i

Rest Of Tonight: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows around 65 near the shore to around 55 above 3000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 78 near the shore to around 64 above 3000 feet. Northeast winds 10 to 35 mph. Gusts up to 60 mph in the afternoon. Chance of rain 70 percent.

Sunday Night: Windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 66 near the shore to around 57 above 3000 feet. Northeast winds 10 to 35 mph with gusts to 60 mph. Chance of rain 70 percent.

South Kaua’i

Rest Of Tonight: Breezy. Cloudy with numerous showers. Locally heavy rainfall possible. Lows around 64. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Sunday: Windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 70 to 78. Northeast winds 20 to 30 mph. Gusts up to 50 mph in the afternoon. Chance of rain 70 percent.

Sunday Night: Windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 66. Northeast winds 20 to 30 mph with gusts to 55 mph. Chance of rain 70 percent.

Kaua’i Mountains

Rest Of Tonight: Breezy. Cloudy with occasional showers. Locally heavy rainfall possible. Lows 55 to 62 in the valleys to around 52 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 80 percent.

Sunday: Very windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 65 to 72 in the valleys to around 56 above 4000 feet. East winds 10 to 30 mph with gusts to 50 mph shifting to the northeast 15 to 40 mph with gusts to 60 mph in the afternoon. Chance of rain 70 percent.

Sunday Night: Very windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 58 to 64 in the valleys to around 54 above 4000 feet. Northeast winds 20 to 40 mph with gusts to 60 mph. Chance of rain 70 percent.

North Kaua’i

Rest Of Tonight: Breezy. Cloudy with occasional showers. Locally heavy rainfall possible. Lows 58 to 66. East winds 10 to 20 mph. Gusts up to 40 mph in the evening. Chance of rain 80 percent.

Sunday: Windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 68 to 77. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Sunday Night: Windy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 60 to 67. East winds 15 to 35 mph with gusts to 60 mph. Chance of rain 70 percent.

East Kaua’i

Rest Of Tonight: Breezy. Cloudy with occasional showers. Locally heavy rainfall possible. Lows 57 to 68. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

Sunday: Windy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 64 to 75. Northeast winds 10 to 20 mph increasing to 15 to 30 mph in the afternoon. Chance of rain 80 percent.

Sunday Night: Windy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 60 to 70. Northeast winds 20 to 30 mph with gusts to 50 mph. Chance of rain 80 percent.

Detailed Forecast

Synopsis

A cold front is slowing as it moves over the Alenuihaha Channel towards the Big Island this afternoon. This frontal boundary combined with increasing moisture and a disturbance aloft, will bring the potential for heavy rainfall, flash flooding, and a few rumbles of thunder through Monday. Breezy north to northeasterly winds will continue to fill in behind the front, with the trades then becoming very windy Sunday into Monday as strong high pressure builds north of the state. Conditions will gradually improve by mid to late next week, though breezy and showery trade wind weather is expected to persist.

Discussion

Satellite and radar imagery this afternoon show mostly cloudy and unsettled conditions across the state. A cold front moved across Kauai and Oahu overnight into the early morning hours, then through Maui County earlier today, bringing gusty north to northeasterly winds in its wake along with periods of moderate to heavy rainfall. As of around 2:30 PM, the front appears to be slowly pushing across the Alenuihaha Channel toward the Big Island.
Over the past 24 hours, north- and east-facing areas of Kauai, Oahu, and Molokai have generally received 2 to 4 inches of rainfall, much of which fell as the front passed through. Rainfall rates have mostly remained manageable, limiting flooding impacts overall. One exception occurred earlier today over Molokai, where higher rates prompted a Flood Advisory. Since then, rainfall rates have eased somewhat, with showers lingering near the frontal boundary and broader stratiform showers streaming northeastward across the western end of the state this afternoon. More recently, heavier showers have developed over the North Kohala district of the Big Island, prompting the issuance of a Flood Advisory there as well.
This front will continue to slow and eventually stall and dissipate in the vicinity of Maui County and the Big Island heading into this evening. This feature will continue to be the main focus for heavy showers through the evening, making the flooding threat locations highly dependent on where this axis of deep moisture and convergence sets up. Then as the front dissipates, the moisture and forcing will become more diffuse across the state, making it harder to pinpoint where and when the heaviest rainfall will occur. High resolution model guidance continues to show windward areas anywhere between Oahu and the Big Island being the main focus for the highest rainfall through Monday, making windward portions of Maui County the most likely to see flooding during this period. However, the flooding threat remains statewide and thus the Flood Watch remains in effect for all islands. With the instability from the upper level disturbance moving overhead, a few isolated thunderstorms may develop within this shower activity, but chances remain low.
In addition to the flooding threat, damaging winds will become a concern late Sunday into Monday as high pressure builds in from the north and a surface trough develops and deepens into a low west of the state. The resulting tightening pressure gradient between these surface features will strengthen the trade winds late Sunday into Monday, with the potential for High Wind Warning level gusts (60+ mph) across mainly leeward downsloping areas or in showers. The main impacts will likely be power outages, downed trees (especially with saturated soils), and difficulty traveling in high-profile vehicles. A High Wind Warning is now in effect for most locations across the state Sunday through Monday.
Finally, winter weather impacts are possible for the Big Island summits this weekend. As deep moisture overspreads the island, an upper level disturbance nudges in from the northwest, and temperatures aloft drop below freezing, conditions will become favorable for heavy snowfall at the summits. As a result, a Winter Storm Warning has been issued for the summits of Mauna Kea and Mauna Loa from Sunday morning through Monday afternoon.
Conditions will gradually improve for the middle and latter portion of next week, although a somewhat showery and breezy trade wind pattern will likely persist.

Aviation

A stalled front over the central part of the state will be enhanced by an upper trough to the west. AIRMET Sierra is posted for tempo mountain obscurations above 2000 feet for all smaller islands and likely continuing tonight into Sunday. MVFR with localized IFR conditions will occur throughout the day. Clouds will likely fill in over the Big Island later today making AIRMET Sierra possible here as well.
AIRMET Tango posted for tempo moderate turbulence across all smaller islands and adjacent waters due to the weather system over the state. Moderate turbulence may occur across all portions of these islands up to FL320.
Light icing is expected in cloud layer 120-FL230 from Kauai to Maui.

Marine

Winds will increase significantly over the next 24 hours. A front currently located near Maui will drift southward and dissipate overnight. As confirmed by ASCAT passes last evening and this morning, robust high pressure building north of the front is driving fresh to strong northeast trade winds along and north of the feature, while weaker easterly flow persists around the Big Island. A Small Craft Advisory (SCA) remains in effect for all waters from Kauai to Maui due to a combination of these winds and large seas in excess of 10 feet, mainly in west-northwest swell. The swell will lower tonight, but the stronger trade winds and the coverage of the SCA will spread to all Hawaiian waters as the front dissipates. As the high builds and low pressure develops several hundred miles southwest of the islands on Sunday, trade winds will strengthen to near gale to gale force over most waters Sunday afternoon through Monday, and the Gale Watch has been upgraded to a Gale Warning for all Hawaiian waters for this time. In addition, expect heavy showers and isolated thunderstorms through Monday. Winds are expected to ease some on Tuesday, but trade will remain in the strong range with some near gales over the windier waters through at least Wednesday.
A large west-northwest swell (295-310 degrees) peaked last night and will gradually lower tonight and Sunday. Buoy observations support downgrading the High Surf Warning (HSW) to a High Surf Advisory (HSA) for exposed north and west facing shores from Kauai to Maui, while the HSA for west facing shores of the Big Island will be extended through tonight. Surf on all islands will decline below HSA thresholds by Sunday morning. Small to moderate north-northwest to northwest swells will prevail through the remainder of the week.
Large and very rough seas will develop on Sunday as trade winds strengthen. East shore surf should rise above the HSA threshold Sunday night, with the potential for surf to reach the HSW level Monday and Tuesday on Kauai and Oahu. Large east shore surf will slowly decline Tuesday into Wednesday but will still remain somewhat elevated through the remainder of the week. Surf along south facing shores will remain small with some small background south-southwest energy expected throughout the first half of next week. Select southern exposures exposed to the wind swell will likely see some larger waves as well.

HFO Watches/Warnings/Advisories

Flood Watch through Monday afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
High Surf Advisory until 6 AM HST Sunday 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.
High Wind Warning from 6 AM Sunday to 6 PM HST Monday for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Winter Storm Warning from 6 AM Sunday to 6 PM HST Monday for Big Island Summits.
Small Craft Advisory until 6 AM HST Sunday for all Hawaiian waters,
Gale Warning from 6 AM Sunday to 6 PM HST Monday for all Hawaiian waters,

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Data Courtesy of NOAA.gov