West Side

Tonight: Mostly cloudy. Isolated showers in the evening. Haze through the night. Lows 68 to 75. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Breezy. Mostly cloudy with isolated showers. Haze. Highs 80 to 85. East winds 10 to 20 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 68 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

South Side

Tonight: Mostly cloudy. Haze. Lows 67 to 76. Northwest winds up to 15 mph.

Monday: Mostly cloudy. Breezy and haze. Highs around 88. North winds up to 10 mph increasing to up to 20 mph in the afternoon.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Lows 67 to 76. North winds 10 to 20 mph.

North Shore

Tonight: Breezy. Mostly cloudy with scattered showers. Haze. Lows around 71 near the shore to around 52 near 5000 feet. East winds up to 20 mph shifting to the southeast 10 to 20 mph after midnight. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 78 to 83 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 70 percent.

Monday Night: Mostly cloudy with scattered showers. Lows around 71 near the shore to around 51 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Central Maui

Tonight: Mostly cloudy. Haze. Lows 67 to 72. East winds 10 to 15 mph.

Monday: Mostly cloudy. Breezy and haze. Highs 82 to 89. East winds 10 to 25 mph.

Monday Night: Mostly cloudy in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 71. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Upcountry

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Haze through the night. Lows around 48 at the visitor center to around 51 at the summit. East winds up to 15 mph increasing to 10 to 20 mph after midnight. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Haze through the day. Highs around 62 at the visitor center to around 70 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

Monday Night: Breezy. Mostly cloudy with scattered showers. Lows around 46 at the visitor center to around 48 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

East Maui

Tonight: Breezy. Mostly cloudy with scattered showers. Haze. Lows around 71 near the shore to around 52 near 5000 feet. East winds up to 20 mph shifting to the southeast 10 to 20 mph after midnight. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 78 to 83 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 70 percent.

Monday Night: Mostly cloudy with scattered showers. Lows around 71 near the shore to around 51 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Lanai City

Tonight: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows around 66. Light winds. Chance of rain 30 percent.

Monday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 72 to 81. East winds up to 10 mph. Chance of rain 40 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows around 65. Northeast winds 10 to 15 mph shifting to the east after midnight.

Kaunakakai

Tonight: Mostly cloudy. Isolated showers in the evening. Haze through the night. Lows 59 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

Monday: Mostly cloudy. Breezy. Haze through the day. Isolated showers in the afternoon. Highs 70 to 88. East winds 10 to 20 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy in the evening, then partly cloudy with isolated showers after midnight. Lows 58 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

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.

Data Courtesy of NOAA.gov