West Side

Today: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 79. South winds 30 to 35 mph with gusts to 55 mph. Chance of rain near 100 percent.

Tonight: Very windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 68 to 73. South winds 25 to 40 mph with gusts to 60 mph. Chance of rain near 100 percent.

Sunday: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 79. South winds 20 to 30 mph. Chance of rain near 100 percent.

South Side

Today: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 80. South winds around 25 mph with gusts to 45 mph. Chance of rain near 100 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 67 to 75. South winds 20 to 25 mph. Chance of rain near 100 percent.

Sunday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 81. South winds 20 to 25 mph. Chance of rain near 100 percent.

North Shore

Today: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 79 near the shore to around 63 near 5000 feet. Southwest winds 20 to 30 mph with gusts to 55 mph. Chance of rain near 100 percent.

Tonight: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 71 near the shore to around 54 near 5000 feet. Southwest winds 20 to 30 mph with gusts to 55 mph. Chance of rain near 100 percent.

Sunday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 80 near the shore to around 63 near 5000 feet. Southwest winds 15 to 25 mph with gusts to 45 mph. Chance of rain near 100 percent.

Central Maui

Today: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 77 to 82. South winds 20 to 25 mph. Chance of rain near 100 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 70. South winds 20 to 25 mph. Chance of rain near 100 percent.

Sunday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 80. South winds 15 to 20 mph. Chance of rain near 100 percent.

Upcountry

Today: Strong winds. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 58 at the visitor center to around 65 at the summit. Southwest winds 35 to 55 mph with gusts to 80 mph. Chance of rain near 100 percent.

Tonight: Strong winds. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 49 at the visitor center to around 45 at the summit. Southwest winds 40 to 60 mph with gusts to 85 mph. Chance of rain near 100 percent.

Sunday: Strong winds. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 59 at the visitor center to around 66 at the summit. Southwest winds 30 to 50 mph. Gusts up to 90 mph decreasing to 80 mph in the afternoon. Chance of rain near 100 percent.

East Maui

Today: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 79 near the shore to around 63 near 5000 feet. Southwest winds 20 to 30 mph with gusts to 55 mph. Chance of rain near 100 percent.

Tonight: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 71 near the shore to around 54 near 5000 feet. Southwest winds 20 to 30 mph with gusts to 55 mph. Chance of rain near 100 percent.

Sunday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 80 near the shore to around 63 near 5000 feet. Southwest winds 15 to 25 mph with gusts to 45 mph. Chance of rain near 100 percent.

Lanai City

Today: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 69 to 76. South winds around 35 mph with gusts to 55 mph. Chance of rain near 100 percent.

Tonight: Very windy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 66. Southwest winds around 40 mph with gusts to 60 mph. Chance of rain 90 percent.

Sunday: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 69 to 75. Southwest winds 25 to 30 mph. Chance of rain near 100 percent.

Kaunakakai

Today: Windy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 66 to 82. South winds 30 to 35 mph with gusts to 55 mph. Chance of rain near 100 percent.

Tonight: Very windy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 58 to 73. Southwest winds 30 to 40 mph with gusts to 60 mph. Chance of rain 90 percent.

Sunday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 66 to 82. Southwest winds 20 to 25 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

A powerful kona storm will remain anchored northwest of the state producing periods of hazardous weather impacts across the Hawaiian Islands through the weekend. Expect a combination of threats ranging from significant flash flooding, damaging winds, strong to severe thunderstorms, and snow and ice over the highest Big Island summits. Strong southwesterly winds will hold today produce damaging wind gusts. The highest threats for damaging winds remain along north and east slopes of island mountains. Unsettled wet weather continues with decreasing southwesterly wind trends from Sunday into next week. This kona storm begins to lift northeastward from Sunday to Monday, heavy rain and strong winds will decrease as severe weather conditions start to ease across the Hawaii region. However, periods of unsettled wet weather in a light and variable low level wind pattern will continue across the state into next weekend.

Discussion

Looking into this mornings satellite water vapor imagery, we continue to see a strong kona storm locked into position northwest of the Hawaiian Islands. Several higher topped cloud bands continue to develop and train over the islands in Maui County and over the Big Island. This satellite picture matches well with latest local radar imagery, indicating the highest rainfall amounts are currently falling across the eastern half of the state at a rate of roughly 1 to 2 inches per hour.
The latest short term forecast guidance shows two negatively tilted upper troughs passing over the islands today. Upper level divergence ahead of each of these troughs will trigger pulses of heavier smaller scale (mesoscale) shower bands potentially training over the islands. These pulses of shower activity will affect each island differently, heavy rainfall will pulse down with decreasing showers after the upper trough passes, and then pulse back up as the next trough moves into the region. The biggest challenge today will be forecasting the intensity and track of these smaller scale heavy rain shower bands, which can significantly alter observed precipitation amounts over any location on an hour by hour basis. Overall we remain in a very unstable weather pattern and additional heavy rain bands will develop over the islands today.
The Flood Watch remains in effect to cover the threats from additional heavy shower bands with the ground already saturated from the large amount of rain that has recently fallen across the state. Strong southwesterly wind gusts will also continue today favoring north and east slopes of island terrain and a High Wind Warning remains in effect. A Winter Storm Warning for snow also continues for the Big Island summits above 12,000 feet elevation.
From Sunday to Monday, the kona storm begins to rapidly weaken and lift northeastward. Strong winds across the state will significantly decrease in the lower elevation areas, and heavy shower activity will diminish in coverage across the region. However, periods of unsettled wet weather in a light and variable low level wind pattern will continue through much of next week.
The extended forecast for next week has evolved over the past 24 hours. A high pressure system is no longer building in north of the region, rather an upper level troughing pattern will continue to dominate Hawaiian Island weather conditions through the end of the week. This means variable light winds each day with periods of showers and possible thunderstorms lasting into next weekend.

Aviation

Widespread showers, some heavy, along with isolated thunderstorms, will continue today. The majority of the showers are forecast to focus on the eastern islands. Expect widespread MVFR to IFR with local LIFR. Winds will remain strong and primarily out of the south to southwest. Widespread gusts up to and over 35 kt are forecast.
AIRMET Sierra remains in effect all islands due to mountain obscuration, and Oahu, Molokai, Maui, and Lanai for IFR. This is expected to remain in effect through tonight.
AIRMET Tango remains in effect for moderate upper-level turbulence between 130 and FL380. and for low-level turbulence due to strong surface winds. Both of these are expected to remain in effect through Saturday.
AIRMET Zulu remains in effect, as high clouds from these showers present icing concerns between FL120 and FL260. This is also expected to continue through Saturday.

Marine

Gale-force winds in the waters near Kauai will continue to decline and the Gale Warning was cancelled for waters around Kauai. Seas will remain elevated in this area so a Small Craft advisory has been issued around Kauai waters. The gales from Oahu to the Big Island will continue in association with the strong kona storm impacting the area. Gusty winds, steep and fast seas, and low visibility in heavy showers will continue across the entire marine waters through the weekend.
These gale force southerly winds will create large and rough surf along south facing shores through this afternoon and as such a High Surf Advisory is in effect for south facing shores until 6 PM. The winds by early next week will shift westerly and diminish as the storm gains increasing distance far to the north of the islands. As the winds diminish the gale warnings will be expired and due to high seas a Small Craft advisory will be expanded to include waters around the smaller islands. Seas will gradually fall as the system moves off to the north.
A small, short to medium period west to west-northwest swell will bring small to moderate surf to north and west facing shores through the weekend. A small, medium period north swell will peak Saturday before gradually declining. The current south swell will continue to decline today and through the weekend.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Kauai County.
Flood Watch through late tonight for Oahu.
Flood Watch through late Sunday night for Maui County and the Big Island.
High Wind Warning until 6 AM HST Sunday for all Hawaiian Islands.
High Wind Warning until 6 PM HST Sunday for Haleakala Summit, Big Island Summits.
Winter Storm Warning until 6 AM HST Monday for Big Island Summits above 12,000 feet elevation.
High Surf Advisory until 6 PM HST this evening for south facing shores of all Hawaiian Islands.
Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Leeward Waters.
Gale Warning until 6 AM HST Sunday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory from 6 AM to 6 PM HST Sunday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

Data Courtesy of NOAA.gov