West Side

Tonight: Mostly cloudy with isolated showers early in the evening, then partly cloudy in the late evening and overnight. Haze through the night. Lows 65 to 72. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 78 to 83. Southwest winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Haze. Lows 66 to 73. South winds up to 10 mph in the evening becoming light.

South Side

Tonight: Mostly cloudy with isolated showers early in the evening, then partly cloudy in the late evening and overnight. Haze through the night. Lows 63 to 74. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs around 85. Southwest winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Haze. Lows 64 to 75. South winds up to 10 mph in the evening becoming light.

North Shore

Tonight: Mostly cloudy with isolated showers early in the evening, then mostly cloudy with scattered showers in the late evening and overnight. Haze through the night. Lows around 68 near the shore to around 51 near 5000 feet. Southeast winds up to 10 mph. Chance of rain 30 percent.

Monday: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 78 to 83 near the shore to around 67 near 5000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Monday Night: Mostly cloudy with scattered showers. Haze. Lows around 69 near the shore to around 51 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Central Maui

Tonight: Mostly cloudy with isolated showers early in the evening, then partly cloudy in the late evening and overnight. Haze through the night. Lows around 66. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 81 to 86. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Haze. Lows around 66. South winds up to 10 mph in the evening becoming light.

Upcountry

Tonight: Mostly cloudy. Isolated showers early in the evening. Haze through the night. Lows 42 to 54. Light winds. Chance of rain 20 percent.

Monday: Partly sunny. Haze through the day. Isolated showers in the afternoon. Highs around 63 at the visitor center to around 68 at the summit. South winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Haze. Lows 42 to 54. South winds up to 10 mph.

East Maui

Tonight: Mostly cloudy with isolated showers early in the evening, then mostly cloudy with scattered showers in the late evening and overnight. Haze through the night. Lows around 68 near the shore to around 51 near 5000 feet. Southeast winds up to 10 mph. Chance of rain 30 percent.

Monday: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 78 to 83 near the shore to around 67 near 5000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Monday Night: Mostly cloudy with scattered showers. Haze. Lows around 69 near the shore to around 51 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Lanai City

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 63. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs 72 to 80. Light winds. Chance of rain 30 percent.

Monday Night: Mostly cloudy with isolated showers. Haze. Lows around 64. South winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Kaunakakai

Tonight: Mostly cloudy with isolated showers early in the evening, then partly cloudy in the late evening and overnight. Haze through the night. Lows 55 to 71. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 70 to 86. South winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy with isolated showers. Haze. Lows 56 to 72. South winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Rain chances will steadily increase through the week as moderate southerly winds associated with an approaching cold front and upper-level disturbance draw deeper moisture northward into the islands. The front may reach the state around Thursday, potentially leading to more widespread rainfall by the weekend.

Discussion

Forecast guidance remains in good agreement through the first half of the week, depicting a deep low pressure system west of the islands gradually shifting east. This will cause low-level winds to veer out of the south and strengthen to moderate speeds beginning Monday. As this pattern evolves, mid- to upper-level heights will lower, and increased moisture will begin streaming northward into the region, initially affecting the western end of the state. As a result, expect mostly cloudy skies at times, with a steady uptick in rain chances through midweek. Humid conditions will persist, and vog is likely to linger due to the continued south to southeast flow.
Confidence is increasing for the latter half of the week as models and ensemble solutions show better alignment. A deep moisture axis and frontal boundary are expected to reach the western islands Wednesday night into Thursday before gradually stalling and weakening. This moisture, combined with broad upper-level troughing and instability, will support a wetter pattern that may become more widespread heading into the weekend. While much of the rainfall will return to typical windward areas as breezy trades reestablish as the surface ridge noses eastward well north of the state, some showers will likely carry over to leeward areas of the smaller islands due to lingering instability and a higher inversion heights.

Aviation

Light southeast to south flow will continue and allow for land breeze development tonight. Isolated light showers may drift over the islands, but not expecting anything widespread. By Monday morning, southerly winds will begin to strengthen to moderate levels, in response to a frontal system approaching the island chain from the northwest. Scattered showers may develop over mainly interior regions during the afternoon with VFR conditions prevailing elsewhere.
All locations can expect to see some VOG with the degassing of Kilauea. It is not impacting vsbys enough to be put into any of the TAFs but is worth mentioning for general awareness.
No AIRMETs in effect.

Marine

A storm system to the distant northwest, will strengthen winds and shift them around to the southeast and south late tonight through Tuesday. Localized terrain enhancement around the Big Island and Kauai will likely result in advisory level winds, and a Small Craft Advisory (SCA) remains in effect for these areas beginning Noon Monday and continuing through 6 PM Tuesday. The SCA may eventually need to be extended through Tuesday night. The winds will gradually ease Wednesday and Thursday as a front approaches from the northwest, with moderate to fresh northeast trades filling in behind the front for the end of the week.
A series of small overlapping north-northeast swells will keep some surf in place along exposed north and east facing shores through midweek. A small west-northwest swell will bring some small surf to exposed north and west facing Tuesday through Thursday. A more significant north-northwest swell appears to arrive late in the week, potentially bringing warning level surf to north and west facing shores next weekend.
Surf along south facing shores will gradually lower tonight, then hold near seasonal levels through late in the week. Surf could become a bit choppy as southerly winds Monday through Wednesday.

HFO Watches/Warnings/Advisories

Small Craft Advisory from noon Monday to 6 PM HST Tuesday for Kauai Northwest Waters, Kauai Leeward Waters, Big Island Windward Waters, Big Island Leeward Waters.

Data Courtesy of NOAA.gov