Photo Credit: Tyler Rooke

West Side

Today: Cloudy and breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 75 to 82. South winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Tonight: Cloudy and breezy. Numerous showers in the evening, then showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows 62 to 68. South winds 10 to 20 mph. Chance of rain 90 percent.

Monday: Breezy. Cloudy with showers and slight chance of thunderstorms. Highs 70 to 77. Southwest winds 10 to 20 mph. Chance of rain 90 percent.

South Side

Today: Cloudy and breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 83. Southwest winds 10 to 20 mph. Chance of rain 30 percent.

Tonight: Cloudy and breezy. Scattered showers in the evening, then numerous showers and isolated thunderstorms after midnight. Lows around 64. Southwest winds 10 to 20 mph. Chance of rain 70 percent.

Monday: Breezy. Cloudy with showers and slight chance of thunderstorms. Highs around 78. South winds 20 to 25 mph shifting to the southwest 10 to 25 mph in the afternoon. Chance of rain 90 percent.

North Shore

Today: Cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 75 to 81 near the shore to around 57 near 5000 feet. South winds up to 15 mph. Chance of rain 30 percent.

Tonight: Cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 62 to 67 near the shore to around 48 near 5000 feet. South winds up to 15 mph. Chance of rain 60 percent.

Monday: Breezy. Cloudy with showers and slight chance of thunderstorms. Highs 70 to 76 near the shore to around 54 near 5000 feet. Southwest winds up to 25 mph. Chance of rain 90 percent.

Central Maui

Today: Cloudy and breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 79 to 84. Southwest winds up to 15 mph increasing to 15 to 20 mph in the afternoon. Chance of rain 30 percent.

Tonight: Cloudy and breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 64. Southwest winds 15 to 20 mph. Chance of rain 70 percent.

Monday: Breezy. Cloudy with showers and slight chance of thunderstorms. Highs 74 to 79. Southwest winds 20 to 25 mph decreasing to 10 to 25 mph in the afternoon. Chance of rain 90 percent.

Upcountry

Today: Cloudy and windy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 52 to 70. Southwest winds up to 25 mph with gusts to 45 mph increasing to up to 35 mph with gusts to 65 mph in the afternoon. Chance of rain 30 percent.

Tonight: Cloudy and windy. Scattered showers in the evening, then numerous showers after midnight. Lows 40 to 51. Southwest winds up to 35 mph with gusts to 65 mph. Chance of rain 60 percent.

Monday: Very windy. Cloudy with showers and slight chance of thunderstorms. Highs 51 to 65. Southwest winds 10 to 45 mph with gusts to 80 mph. Chance of rain 90 percent.

East Maui

Today: Cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 75 to 81 near the shore to around 57 near 5000 feet. South winds up to 15 mph. Chance of rain 30 percent.

Tonight: Cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 62 to 67 near the shore to around 48 near 5000 feet. South winds up to 15 mph. Chance of rain 60 percent.

Monday: Breezy. Cloudy with showers and slight chance of thunderstorms. Highs 70 to 76 near the shore to around 54 near 5000 feet. Southwest winds up to 25 mph. Chance of rain 90 percent.

Lanai City

Today: Cloudy and breezy. Scattered showers in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 70 to 77. South winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Cloudy and breezy. Numerous showers in the evening, then showers and isolated thunderstorms after midnight. Locally heavy rainfall possible after midnight. Lows around 62. Southwest winds 10 to 20 mph. Chance of rain 90 percent.

Monday: Breezy. Cloudy with showers and slight chance of thunderstorms. Highs 68 to 75. Southwest winds 10 to 20 mph. Chance of rain 90 percent.

Kaunakakai

Today: Cloudy and breezy. Scattered showers in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 76 to 83. South winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 64 to 72. South winds 10 to 20 mph. Chance of rain near 100 percent.

Monday: Breezy. Showers and slight chance of thunderstorms. Highs 67 to 77. Southwest winds 10 to 20 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

The potential for heavy rainfall and thunderstorms associated with a front will continue through Monday, initially over the western end of the state through tonight, then over the eastern end on Monday. Conditions will gradually improve from west to east through the first half of the week as high pressure builds to the north in the wake of the front. Breezy southerly winds ahead of the front will hold today, then ease into the light to moderate range as they shift to the north, then to a more typical trade wind direction around midweek. Expect a more typical trade wind pattern to return with showers favoring windward and mauka locations through the second half of the week.

Discussion

The short-term guidance remains in good agreement and depicts the active weather pattern persisting through Monday due to an upper low to the northwest and its attendant surface front forecasted to slowly advance down the island chain. A shortwave pulse rotating through the base of the upper-level trough to the northwest has triggered the next round of heavy showers and storms that is spreading northward over Niihau and Kauai. Provided the saturated soils and elevated streams from the recent heavy rainfall over the past few days, it won't take much for them to respond this morning. Expect this threat to reach Oahu later this morning, then to Maui County later today through Monday. As a result, the Flood Watch has been expanded and now includes all of the smaller islands.
In addition to the expected heavy rainfall, a few thunderstorms could become strong provided the instability and shear profiles, particularly over Kauai and Oahu today. Also, breezy southerly winds could translate to strong downsloping winds over windward areas through this time, especially in the heavy showers/storms moving through.
A drying trend is anticipated from west to east, beginning over Kauai late tonight, then over Oahu through the day Monday as the front advances eastward to Maui County and the Big Island. Conditions should steadily improve over the eastern end of the state Tuesday through Wednesday as the upper level trough exits or shifts northeastward and away from the state. The low-level flow will return to a more typical trade wind direction Wednesday through the second half of the week as surface high pressure builds north of the state.

Aviation

The tail end of a Central Pacific cold front will strengthen as it passes over the western Hawaiian Islands today. An organized band of intense showers associated with with the leading edge of this front can be seen on late night radar slowly approaching western Oahu. These showers, which are accompanied by isolated embedded thunderstorms, are pressing quickly eastward even as they expand to the south.
Surface winds will veer from southeast to west-southwest with the frontal passage. Ahead of the front, light showers will favor south and southeast facing slopes and coasts. Behind the front, moderate showers and embedded thunderstorms will favor west and southwest facing slopes and coasts.
We anticipate issuing AIRMET Sierra for mountain obscuration for Kauai and Oahu later this morning. It will likely need to be expanded to included Molokai and Maui sometime this afternoon.
AIRMET Tango remains for moderate upper level turbulence as been canceled, but conditions are likely to redevelop later today as a new upper level trough approaches from the northwest.
AIRMET Zulu remains in effect for moderate rime icing in cloud, in precipitation, between FL230 and FL280 due to upper level layered clouds. This AIRMET will likely be needed through today and into tonight.

Marine

South to southeast winds will strengthen ahead of an approaching front today. A Small Craft Advisory remains posted for coastal waters west of and including the Kaiwi Channel due to winds. The front will slowly push southeast late today through Monday, before stalling out and slowly dissipating near the Big Island Tuesday and Wednesday. Light to moderate west to northwest winds will fill in behind the front. Winds will become rather light by Monday night and continue through Wednesday, with moderate trades potentially returning for the latter part of the week.
North shore surf will remain small today. Surf will trend up tonight and Monday as a medium-period northwest swell arrives. Surf could reach low end advisory levels along north facing shores Monday night and Tuesday as a second, more north-northwest pulse arrives. This swell will then decline Wednesday through late in the week. Surf along east facing shores will continue to slowly decline today and Monday, with only small very small surf expected through the remainder of the upcoming work week. Small, medium to long period south swell will keep some small surf rolling into south facing shores through late in the week.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for Niihau, Kauai,
Flood Watch through Monday afternoon for Oahu and Maui County.
Wind Advisory from noon today to 6 PM HST Monday for Haleakala Summit.
Winter Weather Advisory until 6 AM HST Monday for Big Island Summits.
High Wind Warning from noon today to 6 PM HST Monday for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel.

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Data Courtesy of NOAA.gov