Hilo

Tonight: Cloudy with numerous showers. Lows 64 to 70 near the shore to 52 to 58 at 4000 feet. East winds up to 10 mph shifting to the northwest after midnight. Gusts up to 30 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 67 at 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 70 near the shore to 50 to 57 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Kona

Tonight: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows around 73 near the shore to 48 to 54 near 5000 feet. Light winds. Chance of rain 50 percent.

Monday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 84 to 89 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows around 72 near the shore to 47 to 52 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows 63 to 72 near the shore to 54 to 62 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs around 80 near the shore to 70 to 79 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Breezy. Partly cloudy with isolated showers. Lows 63 to 71 near the shore to 54 to 62 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows 63 to 72 near the shore to 54 to 62 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs around 80 near the shore to 70 to 79 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Breezy. Partly cloudy with isolated showers. Lows 63 to 71 near the shore to 54 to 62 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

South Big Island

Tonight: Cloudy and breezy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows around 73 near the shore to around 51 near 5000 feet. East winds up to 25 mph shifting to the northeast 10 to 25 mph after midnight. Chance of rain 40 percent.

Monday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs around 87 near the shore to around 66 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Partly cloudy. Breezy. Isolated showers in the evening. Haze through the night. Lows around 73 near the shore to around 51 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Cloudy with numerous showers. Lows 64 to 70 near the shore to 52 to 58 at 4000 feet. East winds up to 10 mph shifting to the northwest after midnight. Gusts up to 30 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 84 near the shore to around 67 at 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 70 near the shore to 50 to 57 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Haze through the night. Lows around 73 near the shore to 51 to 56 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 83 to 89 near the shore to 64 to 72 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Haze. Lows 70 to 76 near the shore to 50 to 55 above 4000 feet. Northeast winds up to 10 mph.

Detailed Forecast

Synopsis

Moderate to locally breezy east-southeast trades will persist through tomorrow as a broad surface trough develops to the west of the state. A disturbance aloft may enhance showers a bit during this time, with showers favoring east and southeast facing slopes and coasts at night, and leeward areas each afternoon. Moderate to locally breezy east-northeast trades will return tomorrow night, focusing showers over windward and mauka areas. This pattern will hold in place through the remainder of the work week, with the trades potentially easing next weekend.

Discussion

This afternoon, the shift to an east-souteast steering flow can be seen on radar and satellite imagery as low level clouds and showers riding in on the trades take on a southeasterly component and move somewhat parallel along the island chain. This veered trade wind flow is the result of a broad surface trough developing to the northwest of the state and interacting with the strong surface ridge centered about 2000 miles north-northeast of Honolulu. In the upper levels, dense cirrus clouds continue to filter across the area from the west-southwest, thanks to an upper level jet streak arching across the region.
This moderate to locally breezy east-southeasterly low level flow pattern is expected to continue through tomorrow. Clouds and showers will favor windward and mauka areas during the overnight to early morning hours and leeward and interior areas during the afternoon hours as sea breezes develop. This flow can also cause low level convergent boundaries that form downstream of each island to provide additional showers to their neighboring downstream islands as they line up along the island chain, as has been the case this afternoon…particularly across Oahu. Shower activity may be slightly enhanced across the western end of the state through tomorrow as both an upper level trough/low dives south to the west of Kauai and brings instability aloft and low level moisture is filtered across the area.
A return to breezy and more stable trade wind conditions is expected by tomorrow night as upper level heights rise, drier air filters in from the east, and the surface trough weakens and moves away from the state. This will result in a more typical easterly trade wind pattern through at least Thursday, with showers favoring windward and mauka areas and generally dry conditions prevailing elsewhere. For the latter end of the week and into the weekend, the trades may ease slightly as a weak upper-level trough moves overhead and another broad surface trough develops west of the state. However, the instability associated with the trough aloft and the available moisture look rather unimpressive, so not expecting much more than perhaps a slight enhancement of trade wind showers for the end of the forecast period at this time.
Vog will continue to filter across the island chain in the east- southeast flow, then transition westward of the smaller islands by midweek as the easterly trades return.

Aviation

Moderate to locally breezy east-southeasterly winds are expected to persist through Monday. Troughing to the west of the islands has significantly increased high clouds today, particularly for the western half of the state (though these high clouds are continuing to spread eastward this afternoon). This has also supported occasional passing showers as moisture embedded within the east-southeast flow moves over the islands at times. While VFR conditions are present at most locations, occasional MVFR ceilings and visibilities have been observed in these passing showers. This pattern will continue into Monday, but background flow will become more easterly again by late Monday.
AIRMET Sierra currently remains in effect for mountain obscuration over Kauai and Oahu this afternoon. This AIRMET will likely continue into the evening and overnight hours.
Additionally, AIRMET Tango remains in effect for moderate low- level turbulence downwind of island terrain. This AIRMET will likely be needed into Monday.

Marine

Fresh east southeast winds forecast through tonight as an upper low and associated surface trough develop west of Hawaii on Monday. A Small Craft Advisory (SCA) is posted for winds over the typical windy waters plus windward Maui waters through Monday. The trough will move westward and the surface ridge to the north will rebuild, causing trade winds to shift back to a more easterly direction. The SCA will likely be reconfigured to the typically windy waters by Monday and should remain in place through at least midweek.
The late season northwest swell will decline tonight and Sunday, with north shore surf dropping to near June average for the first half of the work week. Tiny surf is expected by Thursday.
Surf along south-facing shores will continue to see a mix of small background swell for the next few days, followed by a small inconsistent southwest swell late Tuesday and Wednesday. A long- period south-southwest swell will build on Friday and peak next weekend, leading to surf well above June average.
Surf along east-facing shores will gradually build to near or above seasonal average Monday through Wednesday due to a return of fresh to strong trades over and upstream of the islands.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters.

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Data Courtesy of NOAA.gov