West Side

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 63 to 69. Light winds becoming east up to 10 mph after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 79 to 84. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with scattered showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows 63 to 69. Northeast winds up to 10 mph. Chance of rain 50 percent.

South Side

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then scattered showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows around 64. Light winds. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 85. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows around 64. North winds 10 to 15 mph. Chance of rain 50 percent.

North Shore

Tonight: Frequent showers and slight chance of thunderstorms until early morning, then numerous showers and slight chance of thunderstorms late in the night. Locally heavy rainfall possible. Lows 61 to 67 near the shore to around 47 near 5000 feet. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Friday: Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 76 to 83 near the shore to around 60 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Numerous showers and slight chance of thunderstorms early in the evening, then occasional showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows 61 to 67 near the shore to around 48 near 5000 feet. East winds around 10 mph. Chance of rain 90 percent.

Central Maui

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then scattered showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows 62 to 67. Light winds. Chance of rain 70 percent.

Friday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 81 to 86. East winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows 62 to 67. Northeast winds around 10 mph. Chance of rain 50 percent.

Upcountry

Tonight: Mostly cloudy. Numerous rain showers and slight chance of thunderstorms in the evening, then scattered rain showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows around 40 at the visitor center to around 35 at the summit. Southeast winds up to 10 mph. Chance of rain 70 percent.

Friday: Mostly cloudy. Scattered rain showers and slight chance of thunderstorms in the morning, then numerous rain showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 50 at the visitor center to around 46 at the summit. Southeast winds up to 10 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Numerous showers and slight chance of thunderstorms early in the evening, then isolated showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows around 41 at the visitor center to around 37 at the summit. Light winds. Chance of rain 70 percent.

East Maui

Tonight: Frequent showers and slight chance of thunderstorms until early morning, then numerous showers and slight chance of thunderstorms late in the night. Locally heavy rainfall possible. Lows 61 to 67 near the shore to around 47 near 5000 feet. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Friday: Cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 76 to 83 near the shore to around 60 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Numerous showers and slight chance of thunderstorms early in the evening, then occasional showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows 61 to 67 near the shore to around 48 near 5000 feet. East winds around 10 mph. Chance of rain 90 percent.

Lanai City

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then scattered showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows around 64. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 71 to 78. Light winds. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows around 65. Light winds. Chance of rain 50 percent.

Kaunakakai

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then scattered showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible. Lows 60 to 69. Light winds. Chance of rain 70 percent.

Friday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 76 to 84. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Locally heavy rainfall possible early in the evening. Lows 62 to 71. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A convective pattern with mostly light winds will hold in place during the next couple days, with showers favoring areas near the coast at night and the island interiors during the afternoon and evening hours. Locally heavy rain and a slight chance of thunderstorms is forecast through Friday as an upper low moves over the state. Lingering moisture will likely keep the pattern rather showery, even in leeward areas at times through the weekend. A new storm system could bring another chance for heavy rainfall and thunderstorms to the islands Tuesday and Wednesday.

Discussion

An upper level low continues to build over the state this evening generating significant amount of instability. A surface trough located just west of Kauai is generating light to moderate east to southeast flow over the state with precipitable water values around 1.5 inches. Infrared satellite imagery and radar show mostly cloudy conditions in place with numerous showers and isolated thunderstorms mostly along windward Maui and Oahu with a few showers developing over leeward Big Island and Kauai. Main short term focus revolves around the potential for heavy rain and thunderstorms during the next couple days.
The surface troughing will hold in place into Friday, continuing light to moderate east southeast winds allowing for nighttime land and daytime sea breezes. As the upper low slowly moves eastward tonight into Friday, 500 mb temperatures of -12 to -13 C and precipitable water values around 1.5 to 1.6 inches will continue the threat of heavy showers and isolated thunderstorms across any of the islands. Land breezes may help suppress the heavy rain over the islands by late tonight into Friday morning, but the focus will shift back over the islands by midday Friday. Snow is expected across the high elevation summits of the Big Island and Winter Weather Advisory remains in effect through 6 PM Friday for elevations above 11,000 feet.
The upper low will open up to a trough and weaken through the weekend. Thunderstorms or heavy showers could be possible after Friday given the remnant moisture around the islands, but the atmosphere over Hawaii will begin to stabilize and will lower the chances for this. Precipitable water values continue to hold close to 1.5 inches through the weekend and the latest model trends have been for weak trade winds. As a result, the pattern looks a bit showery through the weekend, with both windward showers, and chances for showers each afternoon and evening in leeward areas as well. A new, potent storm system will bring southerly winds beginning Monday and another round of potentially significant rainfall Tuesday through Thursday.

Aviation

Unstable east-southeast winds will maintain widespread MVFR conditions across most east and southeast slopes with pockets of heavy showers and thunderstorms producing IFR conditions tonight. A surface trough west of Kauai will creep away from the islands on Friday, though will gentle to moderate winds persist out of the east to southeast. An upper-level low, currently centered near Oahu, will drift eastward, maintaining instability statewide tonight, and the greatest chances for heavy showers and thunderstorms shifting to the eastern half of the island chain Friday.
Airmet Sierra is in effect for mountain obscuration over east and south facing areas of Kauai, Oahu, and Maui due to reduced visibility and low ceilings in heavy showers and thunderstorms.
Moderate upper-level turbulence will be possible near and west of the upper low center. AIRMET Tango remains in effect for Kauai and Oahu through midnight and will shift eastward and diminish on Friday.

Marine

Light to moderate east-southeast winds will persist into Friday due to a broad surface trough located west of Kauai. Over the western end of the islands, the light winds will allow a land and sea breeze pattern to continue near the coasts. For the eastern end, light to moderate east to southeast breezes, with localized fresh pockets, will likely persist, particularly around the Big Island. Expect spotty heavy showers and thunderstorms to continue into Friday due to an upper disturbance in the area.
A return to moderate easterly trades is possible by the weekend as high pressure builds to the north. Heavy showers and thunderstorms will remain possible into Friday due to an upper disturbance in the area. Guidance continues to show the trades becoming disrupted and shifting out of the south early next week as deep low pressure sets up nearby to the west
Surf along exposed north and west facing shores is quickly rising this evening as a fresh north-northwest builds down the island chain. Observations at the offshore buoys to the northwest peaked above the predicted levels this afternoon, which will correspond to the surf peaking overnight and into Friday morning. Heights could briefly near warning levels during this peak (around midnight). A downward trend is then expected over the weekend, with the swell shifting out of north.
Surf along east facing shores will remain below the April average through at least Saturday, then steadily rise to around average by early next week.
Surf along south facing shores will remain small, with mainly overlapping background south swells moving through. A larger pulse of south-southwest swell may arrive Tuesday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Friday for Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Winter Weather Advisory until 6 PM HST Friday for Big Island Summits.

Data Courtesy of NOAA.gov