Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny with isolated showers. Highs 82 to 87. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 70 to 77. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 82 to 87. East winds 10 to 20 mph. Chance of rain 50 percent.

South Side

Today: Mostly sunny. Highs around 87. Northwest winds up to 15 mph.

Tonight: Partly cloudy until early morning, then mostly cloudy early in the morning. Lows around 71. North winds up to 15 mph. Chance of precipitation 20 percent.

Monday: Mostly cloudy. Isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 87. North winds up to 15 mph. Chance of rain 40 percent.

North Shore

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 69 to 75 near the shore to around 55 near 5000 feet. Southeast winds up to 15 mph increasing to 10 to 20 mph after midnight. Chance of rain 90 percent.

Monday: Breezy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 79 to 84 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Central Maui

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 86. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows 69 to 74. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly cloudy. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Upcountry

Today: Breezy. Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs around 61 at the visitor center to around 57 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows around 49 at the visitor center to around 45 at the summit. Southeast winds up to 20 mph becoming 10 to 15 mph after midnight. Chance of rain 50 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs around 62 at the visitor center to around 58 at the summit. East winds up to 15 mph. Chance of rain 50 percent.

East Maui

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 69 to 75 near the shore to around 55 near 5000 feet. Southeast winds up to 15 mph increasing to 10 to 20 mph after midnight. Chance of rain 90 percent.

Monday: Breezy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 79 to 84 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Lanai City

Today: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 72 to 81. Light winds becoming east up to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Lows around 68. Northeast winds up to 15 mph becoming around 10 mph after midnight.

Monday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 72 to 81. Northeast winds 10 to 15 mph becoming up to 20 mph in the afternoon. Chance of rain 30 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 75 to 86. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows 62 to 73. East winds 10 to 15 mph. Chance of rain 20 percent.

Monday: Breezy. Mostly cloudy with isolated showers. Highs 75 to 86. East winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Gentle to moderate trade winds will continue through the rest of the weekend, with clouds and passing showers affecting mainly windward and mauka areas. A slug of tropical moisture will bring the potential for locally heavy rain and a few thunderstorms early next week, particularly over Maui and the Big Island. A front then appears to stall over or just north of the islands around the middle of the week while a new high builds to its north. This is expected to bring a period of wet trades and breezy to locally windy conditions to the islands for the latter half of the week.

Discussion

Currently at the surface, a 1028 mb high is centered around 1900 miles northeast of Honolulu, while a trough of low pressure is located around 600 miles southeast of Hilo. Meanwhile, a weakening front is nearly stationary in the vicinity of Midway Atoll, or around 1200 miles west-northwest of Kauai. The local pressure gradient has relaxed over the past 24 hours, with gentle to moderate trades prevailing across the island chain early this morning, with localized land breezes in the more sheltered areas. Infrared satellite imagery shows both high and low clouds moving through the region, with partly cloudy conditions present in most leeward areas and a bit more cloud cover in some windward locales. Radar imagery shows scattered showers moving into windward slopes and coasts, with mainly dry conditions in leeward areas aside for some showers over the leeward slopes and coast of the Big Island. Main short term focus remains on the potential for some locally heavy rain and isolated thunderstorms Monday through Tuesday.
Gentle to moderate trades will hold in place today as high pressure remains to the distant northeast of the islands and the weakening front to the northwest dissipates. The trades should strengthen a bit tonight and Monday as a trough of low pressure slides by to the south of the state, then ease off Monday night and Tuesday as a strong front approaches from the northwest. A new high building in north of the front Tuesday night is expected to lead to a resurgence in the trades, with breezy to locally windy conditions developing by late Wednesday and holding into next weekend.
As for the remaining weather details, fairly typical trade wind weather will prevail through the rest of the weekend, with bands of low clouds and showers affecting windward areas, particularly overnight and during the early morning hours. A few of the showers will reach leeward areas, and the weakened trades could allow a few showers to develop over leeward terrain with the assistance of localized afternoon sea breezes.
A trough passing by south of the state will send a slug of deeper moisture into the eastern end of the state late tonight through Tuesday, which will likely spread to the western islands but to a lesser extent. Meanwhile, upper troughing west of the state will send some shortwave energy across the area, increasing instability and leading to the potential for some locally heavy rainfall and even a slight chance for thunderstorms. At the moment the eastern islands appear to have the highest potential for both locally heavy rain and thunderstorms during this time, with a good amount of ensemble support. A Flood Watch has been issued for the Big Island and Maui beginning late tonight and continuing through Tuesday.
Beyond Tuesday details become less clear. The GFS and the vast majority of its ensemble members continue to show the front approaching and hanging up over or just north of the islands around the the middle of the week. The CMC and ECMWF, along with most of the ensemble members of each model show a more progressive front moving into the islands. The ECMWF even suggests a potential frontal passage pushing clear through the entire island chain. For now will stick with continuity and keep the forecast leaning in favor of the GFS until details become more clear. This results in an extended period of wet trades prevailing into next weekend.

Aviation

Moderate trades to continue through the rest of the weekend. Low cigs and SHRA should impact mainly windward and mauka areas. MVFR conds can be expected in heavier SHRA but otherwise VFR should prevail.
There are currently no AIRMETs in effect.

Marine

Easterly trades have dropped into the moderate to fresh range today as the front approaching from the northwest has weakened the pressure gradient across the state. The Small Craft Advisory (SCA) has been cancelled today for the windier waters and channels over Maui County and the Big Island. A surface trough passing by south of the islands could bring unsettled weather especially around the Big Island waters Monday into Tuesday with the threat of heavy rain and thunderstorms. Also, the trough could bring a brief period of strong winds that could prompt an SCA over the windy waters and channels around Maui County and the Big Island as the trough tightens the gradient tonight into Monday. The aforementioned front may eventually stall over or just north of the islands around midweek bringing strong northeast winds behind it.
North and west facing shores have continued to decline slightly overnight. Recent observations at offshore NDBC Buoy (51101) have begun to pick up the forerunners of the reinforcing swell early this morning. This moderate long period northwest (325 degrees) swell is expected to fill in around mid-morning with surf likely peaking this afternoon into the evening. For a brief period this morning, the surf may drop just below High Surf Advisory (HSA) criteria but will quickly fill back in during the day and as a result the HSA has been extended for north and west facing shores through tonight. The reinforcing swell should steadily decline over the next few days. A series of moderate northwest to north- northwest swells are possible during the second half of the week into next weekend.
Surf along east-facing shores will remain small and choppy with some wrap possible from the northwest swells at select exposures. An upward trend is possible later in the week as the trades strengthen. Surf along south-facing shores will remain small with mainly background energy.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Flood Watch from late tonight through Tuesday afternoon for Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.

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Data Courtesy of NOAA.gov