West Side

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 65 to 71. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Monday: Mostly cloudy with scattered showers. Highs 76 to 82. East winds up to 15 mph. Chance of rain 50 percent.

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

South Side

Tonight: Partly cloudy with isolated showers. Lows 63 to 74. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly cloudy with isolated showers. Highs around 83. North winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Lows 63 to 74. North winds around 10 mph.

North Shore

Tonight: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows around 67 near the shore to around 50 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Frequent showers early in the morning, then scattered showers in the late morning and afternoon. Highs 76 to 81 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Monday Night: Mostly cloudy with scattered showers. Lows around 67 near the shore to around 50 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Central Maui

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 63 to 68. East winds up to 15 mph. Chance of rain 40 percent.

Monday: Mostly cloudy. Breezy. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs 79 to 84. Northeast winds up to 20 mph. Chance of rain 40 percent.

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

Upcountry

Tonight: Mostly cloudy with scattered showers. Lows around 45 at the visitor center to around 41 at the summit. Southeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Mostly cloudy with scattered showers. Highs 55 to 65. East winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows around 45 at the visitor center to around 42 at the summit. Southeast winds up to 15 mph. Chance of rain 50 percent.

East Maui

Tonight: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows around 67 near the shore to around 50 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 90 percent.

Monday: Mostly cloudy. Breezy. Frequent showers early in the morning, then scattered showers in the late morning and afternoon. Highs 76 to 81 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Monday Night: Mostly cloudy with scattered showers. Lows around 67 near the shore to around 50 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Lanai City

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 63. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny early in the morning then becoming mostly cloudy. Highs 71 to 79. Light winds.

Monday Night: Partly cloudy with scattered showers in the evening, then mostly cloudy with isolated showers after midnight. Lows around 63. Light winds. Chance of rain 30 percent.

Kaunakakai

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 55 to 71. East winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Monday: Mostly cloudy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 68 to 84. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 55 to 71. East winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The potential for locally heavy showers and a few thunderstorms will persist into Monday as an upper-level disturbance produces unstable conditions. Light to moderate east-southeast winds will focus rainfall across windward and mauka locations, while daytime sea breezes trigger spotty showers over interior and leeward areas. A return to moderate to breezy easterly trade winds is expected late Tuesday and Wednesday, with showers primarily favoring windward areas through the rest of the week.

Discussion

Short-term model guidance remains in good agreement, indicating that the moist and unstable pattern will persist through Monday as a deep area of low pressure lingers west of the state. Pulses of energy pivoting around this upper low will lead to periods of heavy showers and thunderstorms. While most of this activity will remain to the north where the deep moisture axis is, convergent southeast flow interacting with our island terrain will keep the potential high for localized heavy showers and storms developing and anchoring periodically. This scenario has quickly evolved over the windward side of Oahu this evening, where a 2 to 4 inches have fallen within the past few hours. Model reflectivities have initialized well with this activity and depict it continuing off and on through the overnight hours for Oahu, with additional activity develop and lifting northward toward Kauai and Oahu. Elsewhere, mostly quiet conditions are likely overnight, with mainly light to moderate windward showers expected over Maui County and the Big Island.
The moist and unstable east-southeast flow will persist on Monday, but chances for widespread heavy rainfall will slowly diminish. The upper-level trough stretching over the region will begin to slowly weaken, allowing the mid levels to warm slightly, and the zone of low-level convergence will lift farther north. Expect continued windward rainfall with spotty afternoon showers leeward, but with less potential for heavy rainfall.
By midweek, a return to moderate to breezy trade winds is expected as high pressure builds to the north and the surface low west of the state moves farther away. Meanwhile, the upper low will weaken into an open trough as it drifts eastward over the region from Tuesday through Thursday. This pattern will shift showers back to the typical windward and mauka locations statewide, especially as pockets of low-level moisture move through. More stable conditions are anticipated later in the week as upper heights rise and the weakening upper trough exits east of the state.
The long-term guidance is now in slightly better agreement for next weekend, and shows the trades easing with a cold front approaching the region.

Aviation

Light to moderate ESE winds with localized land/sea breezes should continue tonight through tomorrow as a surface low and trough linger to the west of the Hawaiian Islands. There is some marginal instability due to broad upper level troughing. Expect SHRA and a few isol -TSRA to affect mainly windward and mauka areas, with localized sea breezes leading to a few SHRA over leeward locations as well. IFR/MVFR conds can be expected SHRA. Elsewhere VFR conds should prevail.
AIRMET Sierra is in effect for mtn obsc for all of Kauai and windward portions of the rest of the islands.

Marine

An area of low pressure just northwest of the state is generating light to moderate east-southeast winds over the western half of the state and moderate to locally fresh east southeast winds over the eastern half. Isolated thunderstorms are possible through Monday, mainly for the western waters, due to the proximity of the low. As the low weakens and drifts westward Monday and Tuesday, a couple of strong high pressure systems will pass north of the state. Winds will gradually back to a more typical easterly direction and increase to moderate to locally fresh speeds statewide by Tuesday night, before becoming locally strong during the second half of the week when Small Craft Advisories are likely for the winds and rough seas.
A small, medium-period north-northwest swell (340-350 degree) is expected to arrive and peak Monday then slowly fade into Wednesday, providing a boost in surf for north and some exposed west facing shores. In the long range, a series of small, long- period northwest (310-330 degree) swells look to keep surf from going flat for north and west facing shores Tuesday through much of next week.
Expect choppy surf along east facing shores through early next week. East shore surf may pick up a notch or two by midweek as wind speeds increase locally and upstream. A small boost in south shore surf may start as early as Monday night as series of small, long-period south swells move through the state through the upcoming week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov