West Kaua’i

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then showers after midnight. Lows 62 to 67 near the shore to around 55 above 3000 feet. North winds up to 20 mph. Chance of rain 90 percent.

Saturday: Cloudy and breezy. Showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to around 64 above 3000 feet. Northeast winds 10 to 20 mph decreasing to up to 20 mph in the afternoon. Gusts up to 45 mph. Chance of rain 80 percent.

Saturday Night: Breezy. Cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 65 near the shore to around 55 above 3000 feet. Northeast winds up to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 64. North winds 10 to 15 mph shifting to the northeast 15 to 25 mph after midnight. Chance of rain 70 percent.

Saturday: Cloudy and breezy. Numerous showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 71 to 78. Northeast winds 20 to 25 mph. Gusts up to 50 mph in the afternoon. Chance of rain 70 percent.

Saturday Night: Breezy. Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 64. Northeast winds 20 to 25 mph with gusts to 50 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Breezy and showers. Lows 55 to 64 in the valleys to around 52 above 4000 feet. North winds up to 20 mph shifting to the northeast 10 to 20 mph after midnight. Chance of rain near 100 percent.

Saturday: Breezy. Showers in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 64 to 71 in the valleys to around 55 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Saturday Night: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 56 to 63 in the valleys to around 52 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 80 percent.

North Kaua’i

Tonight: Breezy and showers. Lows 57 to 65. North winds 10 to 25 mph. Chance of rain near 100 percent.

Saturday: Breezy. Showers in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 66 to 76. Northeast winds 10 to 25 mph with gusts to 45 mph. Chance of rain near 100 percent.

Saturday Night: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 57 to 65. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 80 percent.

East Kaua’i

Tonight: Showers. Lows 58 to 67. North winds up to 15 mph shifting to the northeast after midnight. Chance of rain near 100 percent.

Saturday: Breezy. Showers in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 64 to 75. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Saturday Night: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 58 to 68. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

Detailed Forecast

Synopsis

A cold front will move into Kauai by this evening, then slow and stall near Maui County on Saturday. This frontal boundary combined with increasing moisture and a disturbance aloft, will bring the potential for heavy rainfall, flash flooding, and a few thunderstorms from Saturday afternoon through Monday. Breezy north to northeasterly winds will develop behind the front, then the trades will become very windy late Sunday into Monday as strong high pressure builds well north of the state and interacts with a deepening trough to the west. Conditions will gradually improve by mid to late next week, though breezy and occasionally showery trade wind weather is expected to persist.

Discussion

Visible satellite imagery this afternoon highlights two key features impacting the forecast: a cold front on Kauais doorstep and a plume of moisture lifting northward across the central islands within a weakly convergent southwesterly flow.
The cold front is expected to move across Kauai late this afternoon or early this evening, then continue gradually down the island chain toward Oahu late tonight before slowing and stalling near Maui County on Saturday. Shower coverage will increase along and ahead of the front, with the greatest potential for heavy rainfall tonight across north- and east-facing areas of Kauai. Some high-resolution model guidance suggests rainfall totals of 1 to 3 inches in these areas by Saturday morning. Meanwhile, isolated to scattered showers will continue to filter across the central islands on the weakly convergent southwesterly flow. As the front reaches Oahu late tonight and Maui County on Saturday, showers will increasingly focus over windward and mauka areas.
As the front stalls and begins to weaken over Maui County on Saturday, it will interact with the weak surface convergence zone embedded in the southwesterly flow ahead of it. This interaction will lead to expanding shower coverage statewide. With deep moisture supplied by these two features spreading across the islands and increasing instability as much cooler air filters in aloft with an upper level disturbance, the threat for heavy rain and flooding will rise, particularly over windward and mauka areas. Model guidance suggests that some of these areas may receive 3 to 6 inches of rain from tonight through Monday. Isolated thunderstorms will also be possible within the more robust shower bands. A Flood Watch remains in effect for all islands from noon Saturday through 6 PM Monday.
In addition to the flooding threat, winds also become a concern Sunday into Monday as high pressure builds in behind the front and a surface trough forms and deeps west of the state. The tightening pressure gradient between these surface features will strengthen the trade winds likely to Wind Advisory criteria late Sunday into Monday, with the potential for isolated High Wind Warning level gusts across some leeward downsloping areas.
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 Watch remains in effect for the summits of Mauna Kea and Mauna Loa from Saturday afternoon 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 strong cold front is moving through Kauai this afternoon, and a separate band of moisture is moving southwest to northeast over Maui County. The front will bring low clouds, showers and strengthening north winds to Oahu this evening, Maui County tonight and the Big Island Saturday. MVFR, with localized IFR conditions, will occur as the front moves through.
AIRMET Sierra is in effect for tempo mountain obscurations above 2500 feet for Molokai, Lanai and Maui, and will likely linger into the evening. Kauai is most likely to be added later this afternoon or evening due to arrival of the front.
AIRMET Tango for turbulence will likely become necessary tonight and Saturday as winds increase, starting with Kauai and spreading eastward.

Marine

A front currently near Kauai will move to Oahu waters tonight, then stall and dissipate over Maui County waters Saturday. High pressure building behind the front will produce fresh to strong northeasterly trade winds around Kauai and Oahu tonight and expand to Maui County waters Saturday. A Small Craft Advisory (SCA) remains in effect around Kauai and Oahu for a combination of the increasing winds and combined seas in excess of 10 feet from a building west-northwest swell. The SCA has been expanded to Maui County waters Saturday. Over Big Island waters, gentle to moderate southerly winds will give way to strengthening easterly winds on Saturday. As the high expands later in the weekend, trade winds will strengthen to near gale to gale force over most waters late Sunday and Monday. While the SCA now runs through Sunday afternoon, it will need to be expanded to all Hawaiian waters and extended through at least Monday, and a Gale Watch may be issued overnight for some waters. In addition, expect heavy showers and isolated thunderstorms over most waters Saturday through Monday. Winds are expected to ease Tuesday but still remain in the fresh to strong range through Wednesday.
A large west-northwest swell (295-310 degrees) will build down the island chain through the evening and peak late tonight into early Saturday. Recent observations at NOAA buoys northwest of Kauai indicate that the swell is coming in a couple of feet larger than guidance at 14 to 16 feet with significant energy spread between 13 to 19 second periods. A High Surf Warning (HSW) remains in place for rapidly rising surf across north and west facing shores of Niihau, Kauai, Oahu, and Molokai this afternoon and evening, and given the larger swell, the HSW has been expanded to north shores of Maui. The swell will reach west facing shores of the Big Island around sunrise, and a High Surf Advisory is in effect for that area through at least the afternoon. The swell will decline sharply late Saturday, with surf expected to fall below advisory levels on all shores by Sunday morning. Small to moderate north-northwest swells will prevail through the remainder of the week.
Surf along east facing shores will remain very small into the evening. East shore surf will build and become rough from west to east late tonight and Saturday as the front moves down the island chain. Large and very rough seas will develop on Sunday as trade winds strengthen, likely exceeding the advisory level Sunday night or Monday and potentially reaching the warning level. Large east shore surf will slowly decline Tuesday through the remainder of the week. Surf along south facing shores will remain small with a slight bump possible early next week.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Flood Watch from Saturday afternoon 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 Wind Watch from Sunday morning through Monday afternoon for Kauai Leeward, Kauai Mountains, Waianae Coast, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Leeward West, Kohala, Big Island Interior, Kauai South, Honolulu Metro, Ewa Plain, Koolau Leeward, Molokai West, Molokai Leeward South, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South.
High Surf Advisory from 6 AM to 6 PM HST Saturday for Kona, Kohala.
Winter Storm Watch from Saturday afternoon through Monday afternoon for Big Island Summits.
Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.
Small Craft Advisory from 6 AM Saturday to 6 PM HST Sunday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

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Data Courtesy of NOAA.gov