West Side

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible in the evening. Lows 65 to 71. Light winds. Chance of rain 50 percent.

Saturday: Mostly sunny with scattered showers and slight chance of thunderstorms early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs 76 to 81. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 65 to 72. Northeast winds around 10 mph. Chance of rain 50 percent.

South Side

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms in the evening, then partly cloudy with slight chance of thunderstorms and isolated showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 74. Light winds. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Slight chance of thunderstorms early in the morning. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 85. Light winds becoming north around 10 mph in the afternoon. Chance of rain 30 percent.

Saturday Night: Mostly clear. Isolated showers after midnight. Lows 64 to 74. Light winds. Chance of rain 20 percent.

North Shore

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then occasional showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible in the evening. Lows around 68 near the shore to around 49 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy. Slight chance of thunderstorms early in the morning. Occasional showers in the morning, then numerous showers in the afternoon. Highs 76 to 82 near the shore to around 65 near 5000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Saturday Night: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows around 68 near the shore to around 50 near 5000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Central Maui

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms in the evening, then partly cloudy with slight chance of thunderstorms and isolated showers after midnight. Locally heavy rainfall possible in the evening. Lows around 66. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Slight chance of thunderstorms early in the morning. Isolated showers in the morning, then scattered showers in the afternoon. Highs 79 to 86. Northeast winds up to 10 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy with isolated showers. Lows around 66. Northeast winds around 10 mph. Chance of rain 20 percent.

Upcountry

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms in the evening, then partly cloudy with slight chance of thunderstorms and isolated showers after midnight. Locally heavy rainfall possible in the evening. Lows around 44 at the visitor center to around 38 at the summit. Light winds. Chance of rain 70 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Slight chance of thunderstorms early in the morning. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 59 at the visitor center to around 61 at the summit. Light winds. Chance of rain 50 percent.

Saturday Night: Partly cloudy with scattered showers. Lows around 44 at the visitor center to around 41 at the summit. Light winds. Chance of rain 50 percent.

East Maui

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then occasional showers and slight chance of thunderstorms after midnight. Locally heavy rainfall possible in the evening. Lows around 68 near the shore to around 49 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 90 percent.

Saturday: Mostly cloudy. Slight chance of thunderstorms early in the morning. Occasional showers in the morning, then numerous showers in the afternoon. Highs 76 to 82 near the shore to around 65 near 5000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Saturday Night: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows around 68 near the shore to around 50 near 5000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Lanai City

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms in the evening, then partly cloudy with slight chance of thunderstorms and isolated showers after midnight. Locally heavy rainfall possible in the evening. Lows 61 to 66. Light winds. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming mostly cloudy. Slight chance of thunderstorms early in the morning. Isolated showers in the morning, then numerous showers in the afternoon. Highs 71 to 79. Light winds. Chance of rain 60 percent.

Saturday Night: Mostly clear. Lows around 64. Light winds.

Kaunakakai

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms in the evening, then partly cloudy with slight chance of thunderstorms and isolated showers after midnight. Locally heavy rainfall possible in the evening. Lows 55 to 71. Light winds. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Slight chance of thunderstorms early in the morning. Isolated showers in the morning, then scattered showers in the afternoon. Highs 68 to 85. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Partly cloudy with isolated showers. Lows 55 to 71. East winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

An active convective pattern with mostly light winds will continue through this evening, with showers and thunderstorms favoring island interiors, then transitioning to mostly windward areas overnight. Moderate trades are expected to return tomorrow and persist through the weekend, with lingering moisture and instability maintaining a rather showery pattern across the island chain. A new storm system will disrupt the trades once again and bring another chance for heavy rainfall and thunderstorms to the islands Tuesday through Thursday.

Discussion

A cold core upper level low remains centered near Maui County this afternoon and will gradually begin to push eastward tonight. The instability this upper level feature is providing to the state combined with ample lingering moisture (PWats over 1.5 inches as measured on this afternoon's upper air soundings) has lead to heavy showers and thunderstorms impacting the majority of the state throughout the day today, which caused flash flooding across portions of Kauai, Oahu and Maui County. High resolution models indicate that heavy rain and thunderstorms will persist through this evening. In addition, snow is expected across the high elevation summits of the Big Island and the Winter Weather Advisory has been extended through 6 AM Saturday for elevations above 11,000 feet.
At the surface, a strong high pressure system to far north and weakening surface trough retreating to west will bring light to moderate southeast winds through this evening. This lighter flow will allow land breezes to help to push some of the shower and thunderstorm activity offshore overnight. Showers caught up in the southeast flow will also periodically move into windward areas, particularly during the overnight hours, and occasionally pass over into leeward areas.
Over the weekend, moderate easterly trades will return as the surface trough pushes further away and dissipates, allowing the high pressure system to the north to take more control of the local winds. Aloft, we'll lose some of the instability as the upper low opens into a trough, weakens and pushes further eastward, but showers are expected to stick around as moisture lingers. As a result, expect a showery tradewind pattern through the weekend, with showers occasionally spilling over to leeward areas.
A new, potent storm system will disrupt the tradewind flow much of next week bringing light to moderate southeasterly winds back to the area late Monday into Tuesday and another round of potentially significant rainfall Tuesday through Thursday.

Aviation

Interior showers and thunderstorms are bringing widespread MVFR to Oahu through Maui and portions of the Big Island with pockets of IFR within more intense activity. SHRA/TSRA will gradually dissipate this evening with the loss of diurnal heating. The development of land breezes tonight will accelerate clearing, though convective debris will likely contribute to a mid-level/VFR cloud deck that will persist well into tonight. Moderate trades return early Saturday, but will not be strong enough to eliminate the inland shower threat. Instead, the resulting hybrid sea breeze pattern will focus moderate to locally heavy showers over western portions of the smaller islands, particularly Oahu and Maui.
AIRMET Sierra remains in effect for the islands of Oahu, Molokai, and Maui.

Marine

High pressure far to the northeast will gradually strengthen through the weekend. Light east to southeast winds across Hawaii will become light to moderate east to northeast winds by tomorrow night. Trade wind flow will predominate Sunday and Monday, but a deep low developing to the northwest of the state will disrupt that flow on Tuesday. Winds will yet again weaken and shift to be out of the south or southeast and remain so through most of the week.
Meanwhile, a passing upper level disturbance has triggered isolated to scattered thunderstorms across much of the state. These storms are capable of producing strong gusty winds, locally heavy downpours, and small hail. The potential for strong thunderstorms will persist through tonight and possibly beyond.
A lingering north-northwest swell that peaked last night will continue its gradual decline through Saturday. On Sunday, surf along north and west facing shores will dip below average, then remain so well into next week. Guidance does depict a gale forming on Monday near the Kurils, then tracking northeast to the western Aleutians by Wednesday. If this materializes, Hawaii could experience an uptick in the northwest swell next weekend.
Surf along east facing shores will remain below the April average through most of next week due to the lack of consistent trade wind flow.
A small long period background south swell will move through this weekend, but will have little impact on surf heights. A larger pulse of long-period south- southwest swell is expected for the coming week.

HFO Watches/Warnings/Advisories

Winter Weather Advisory until 6 AM HST Saturday for Big Island Summits.

Data Courtesy of NOAA.gov