West Side

Today: Breezy. Showers and isolated thunderstorms. Highs 71 to 82. South winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows 65 to 73. South winds 10 to 20 mph. Chance of rain 90 percent.

Saturday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 71 to 81. South winds up to 20 mph. Chance of rain near 100 percent.

South Side

Today: Breezy. Mostly cloudy with showers and isolated thunderstorms. Highs 73 to 83. Southwest winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows around 69. South winds 10 to 20 mph. Chance of rain 80 percent.

Saturday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 72 to 82. South winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain near 100 percent.

North Shore

Today: Partly sunny with showers likely and isolated thunderstorms. Highs around 81 near the shore to around 67 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows around 71 near the shore to around 56 near 5000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 70 percent.

Saturday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 78 to 83 near the shore to around 66 near 5000 feet. West winds up to 15 mph. Chance of rain near 100 percent.

Central Maui

Today: Breezy. Partly sunny with showers likely and isolated thunderstorms. Highs around 82. Southwest winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with showers likely and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows around 69. South winds up to 20 mph. Chance of rain 70 percent.

Saturday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 81. South winds up to 15 mph. Chance of rain near 100 percent.

Upcountry

Today: Breezy. Showers and isolated thunderstorms. Highs 51 to 69. Southwest winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows around 47 at the visitor center to around 43 at the summit. Southwest winds 10 to 20 mph. Chance of rain 90 percent.

Saturday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 50 to 68. Southwest winds 10 to 20 mph. Chance of rain near 100 percent.

East Maui

Today: Partly sunny with showers likely and isolated thunderstorms. Highs around 81 near the shore to around 67 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows around 71 near the shore to around 56 near 5000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 70 percent.

Saturday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 78 to 83 near the shore to around 66 near 5000 feet. West winds up to 15 mph. Chance of rain near 100 percent.

Lanai City

Today: Windy. Showers and isolated thunderstorms. Highs 67 to 76. South winds 15 to 30 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows 60 to 66. South winds 15 to 25 mph. Chance of rain 90 percent.

Saturday: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 66 to 75. Southwest winds 10 to 25 mph. Chance of rain near 100 percent.

Kaunakakai

Today: Breezy. Showers and isolated thunderstorms. Highs 66 to 83. Southeast winds 10 to 20 mph shifting to the south up to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible in the late evening and overnight. Lows 56 to 71. South winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain near 100 percent.

Saturday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 64 to 81. South winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

In the big picture, two surface low pressure systems will move slowly northeastward through the northern Hawaii region into the weekend, producing additional periods of moderate to heavy rain, thunderstorms, and elevated threats for flash flooding. A combination of low level forcing and passing upper level troughs will drive these smaller scale heavy rain band and thunderstorm formations. Additional weather threats include strengthening south to southwest kona winds on Saturday that will produce down sloping wind gusts in the 30 to 45 MPH range along steep north and east slopes of island mountain ranges lasting through Saturday night. Improving weather trends will develop from west to east on Monday as we transition to a wet trade wind weather pattern lasting through the end of next week.

Discussion

A large slow moving band of heavy showers and thunderstorms has produced 5 to 10 inches of rainfall over the past 6 hours across the northern half of Oahu, widespread catastrophic flooding is occurring. Travel in and out of Haleiwa has been cut off due to high flood waters in the area.
The satellite and radar imagery this morning shows a slow moving band of heavy showers and thunderstorms over northern Oahu that brought widespread flooding to the northern half of the island continues to drift eastward. A few showers are back building over the island with additional rainfall rates in the 1 to 2 inches per hour range. This mesoscale convective system are passing north of the islands in Maui County this morning. However, we will need to closely monitor the track of this slow moving system for possible flooding threats to both islands as it continues to drift east through the Hawaii region.
Upper level troughing and a subtropical jet stream north of the islands continues to provide divergence aloft to help trigger heavier showers and a few thunderstorms over the next 24 hours. Threats for heavy showers and flooding will increase across the state into Saturday with the kona low drifting closer to Kauai. A combination of low level forcing and passing upper level troughs will drive these smaller scale heavy rain band and thunderstorm formation. Some of these thunderstorms may become severe as wind shear and strong instability may lead to rotating strong thunderstorms producing damaging wind gusts and heavy rain threats. The latest weather model guidance remains fairly consistent with this kona low, increasing our confidence of an extended period of moderate to heavy rain falling across the state along with periods of thunderstorms lasting into Sunday. A Flood Watch remains in effect for all Hawaiian Islands through Sunday afternoon.
Additional threats include strengthening south to southwest kona winds on Saturday that will produce down sloping wind gusts in the 30 to 45 MPH range along steep north and east slopes of island mountain ranges lasting through Saturday night. These strong wind gusts will likely uproot trees, as roots give way under saturated ground conditions, tree branches will break and fall, potentially producing another round of power outages for some local island communities.
Periods of icing and snowfall on the Big Island summits are possible above 12,000 feet elevation level along with strong gusty winds during the Saturday night through Sunday time period.
Improving weather trends will develop from west to east on Monday as we transition to a cool, wet and breezy trade wind weather pattern lasting through the end of next week.

Aviation

Conditions have deteriorated across the state as bands of rain with embedded heavy showers and storms develop and move through. These rainbands are producing periods of IFR to LIFR CIGS/VSBYS, which will persist in the weekend as an upper trough approaches from the west.
Low-level winds will continue to veer to the south-southwest and strengthen, especially at exposed terminals. These winds may result in localized mechanical turbulence leeward of terrain.
AIRMET Sierra for mountain obscuration is now in effect across all islands and will likely continue into the weekend. AIRMET Zulu for light icing in the 130-FL260 layer will continue to be a concern within deeper cloud layers associated with the upper disturbance.

Marine

Light to moderate southerly winds will strengthen tonight as surface low pressure roughly 300 nm west of Kauai and an associated front stretching north of the state deepen. Moderate to locally strong south to southwest winds will prevail Friday and Saturday, and periods of heavy showers and thunderstorms are expected. The low will lift to the north of the state on Sunday, likely allowing moderate northerly winds and lower chances for rainfall to develop around Kauai. On Monday, high pressure building north of the state will push a surface trough eastward over the islands. Fresh to strong northeast winds may require a Small Craft Advisory (SCA) over most waters, though variable winds could linger around the Big Island through the day. Fresh to potentially strong trade winds will persist on Tuesday.
Buoys are showing the north swell is a bit larger than expected at around 5 feet 11 seconds, and this swell is only expected to increase through the day and into Saturday, which will keep moderate swell going through the weekend along north facing shores. A small, overlapping west-northwest swell is expected to arrive late Saturday and hold into Monday as well. Aside from areas exposed to wrapping north swell, surf along east facing shores will remain well below average through the weekend. Early next week, the development of northeasterly trade winds could bring a potentially larger pulse of medium period north-northeast swell. This will allow rough surf to return to east facing shores, which may approach High Surf Advisory level.
A moderate south swell will slowly diminish today, followed by a small reinforcing south-southwest swell this weekend into Monday. Smaller surf is expected along south facing shores through the remainder of the week.

HFO Watches/Warnings/Advisories

Flood Watch through Sunday afternoon for all Hawaiian Islands.

Data Courtesy of NOAA.gov