Hilo

Tonight: Mostly cloudy. Isolated showers early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Lows 62 to 69 near the shore to 50 to 56 at 4000 feet. South winds up to 10 mph. Chance of rain 30 percent.

Monday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Haze through the day. Highs around 82 near the shore to 66 to 72 at 4000 feet. South winds up to 20 mph. Chance of rain 30 percent.

Monday Night: Partly cloudy with scattered showers. Haze. Lows 62 to 70 near the shore to 50 to 57 at 4000 feet. South winds up to 15 mph. Chance of rain 30 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 70 near the shore to 45 to 52 near 5000 feet. 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 around 86 near the shore to around 68 near 5000 feet. West winds up to 10 mph. Chance of rain 30 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 71 near the shore to 45 to 52 near 5000 feet. Light winds. Gusts up to 25 mph in the evening. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy with isolated showers early in the evening, then mostly cloudy in the late evening and overnight. Haze through the night. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. Light winds becoming southwest up to 10 mph after midnight. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Haze through the day. Highs around 78 near the shore to 69 to 76 near 3000 feet. Northwest winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Haze. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. Light winds.

Kohala

Tonight: Mostly cloudy with isolated showers early in the evening, then mostly cloudy in the late evening and overnight. Haze through the night. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. Light winds becoming southwest up to 10 mph after midnight. Chance of rain 20 percent.

Monday: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Haze through the day. Highs around 78 near the shore to 69 to 76 near 3000 feet. Northwest winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Haze. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. Light winds.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 71 near the shore to around 49 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs around 84 near the shore to around 69 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 30 percent.

Monday Night: Breezy. Partly cloudy with isolated showers. Haze. Lows around 72 near the shore to around 50 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Isolated showers early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Lows 62 to 69 near the shore to 50 to 56 at 4000 feet. South winds up to 10 mph. Chance of rain 30 percent.

Monday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Haze through the day. Highs around 82 near the shore to 66 to 72 at 4000 feet. South winds up to 20 mph. Chance of rain 30 percent.

Monday Night: Partly cloudy with scattered showers. Haze. Lows 62 to 70 near the shore to 50 to 57 at 4000 feet. South winds up to 15 mph. Chance of rain 30 percent.

Waikoloa

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 71 near the shore to 49 to 54 above 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny in the morning then becoming mostly cloudy. Isolated showers. Haze. Highs 81 to 88 near the shore to 64 to 71 above 4000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy with isolated showers. Haze. Lows 69 to 74 near the shore to 49 to 54 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Rain chances will steadily increase through the week as southerly winds associated with a cold front and upper disturbance draw moisture northward into the islands. This front may reach the islands around Thursday, potentially leading to more widespread rainfall into next weekend.

Discussion

A nearly stationary, deep low pressure system is centered around 1200 miles northwest of Kauai. A jet stream along the eastern flank of this system will bring cirrus clouds over much of the state, particularly the western half into Monday. At the surface, a weak high is located about 2000 miles to the east, with a long ridge axis that passes just north of Hawaii. Gentle southeast winds will be the result of the ridge to the east tonight with land breezes decreasing low clouds over the island interiors tonight. Vog will carry up from the Big Island to the smaller islands over the next several days.
The low pressure system and associated cold front will begin to move closer to the islands Monday and Tuesday. Southerly winds will strengthen and bring increased moisture initially over the western end of the state as early as tonight and over the next few days. Clouds and showers will focus over leeward and south facing slopes (southeast for Big Island).
Winds will taper off and veer southwesterly as the front nears the western end of the state allowing land and sea breezes to take over again. The front may reach Kauai around Thursday and begin to stall and weaken into Friday with trade winds filling in over the frontal boundary, potentially leading to more widespread rainfall into next weekend.

Aviation

Light southeast flow will continue and allow for sea/land breeze development through tonight. Some isol SHRA and MVFR conds along interior leeward portions today. VFR conds expected to prevail through the period.
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 was worth mentioning for general awareness.
No AIRMETs in effect.

Marine

A surface ridge lingering over the region will keep winds light and variable over the western end of the state and light to moderate east- southeasterly over the eastern end of the state through tonight. Deep low pressure and an associated cold front currently northwest of the state will move east towards the islands, strengthening winds and shifting them to a more southerly/southeasterly direction Monday through Tuesday. Localized terrain enhancement around the Big Island and western Kauai waters are expected to produce south to southeasterly winds up to 25 kt. Therefore a small craft advisory has been put into effect for that time period. The winds are expected to gradually ease Wednesday and Thursday as the front weakens and its associated low pressure moves north. Models indicate that the front will wash out over the western end of the state towards the end of the week, with with moderate to fresh northeast trades filling in behind it.
A series of small overlapping north-northeast swells will keep surf in place along exposed north and east facing shores through mid week. A small west-northwest swell will bring some small surf to exposed north and west facing shores Tuesday through Thursday. A more significant north-northwest swell appears to arrive late in the week, potentially bringing warning level surf next weekend.
Surf along south facing shores will gradually decrease tonight through the week and could become choppy with increasing southerly winds on Monday and Tuesday.

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.

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Data Courtesy of NOAA.gov