Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny with isolated showers. Highs 82 to 90. East winds up to 15 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 68 to 75. East winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny with isolated showers. Highs 80 to 89. East winds 10 to 20 mph. Chance of rain 20 percent.

South Side

Today: Partly sunny in the morning then becoming sunny. Breezy. Highs around 90. North winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Lows around 70. North winds 10 to 20 mph.

Tuesday: Sunny and breezy. Highs around 89. Northeast winds 10 to 20 mph.

North Shore

Today: Mostly cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 81 to 88 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with showers. Lows 67 to 72 near the shore to around 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Tuesday: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 80 to 86 near the shore to around 66 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Central Maui

Today: Breezy. Partly sunny with scattered showers in the morning, then sunny in the afternoon. Highs around 90. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 68 to 73. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Breezy. Isolated showers in the morning. Highs around 88. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 62 at the visitor center to around 57 at the summit. East winds around 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 47 at the visitor center to around 43 at the summit. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 60 at the visitor center to around 55 at the summit. Light winds becoming east 10 to 15 mph in the afternoon. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 81 to 88 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with showers. Lows 67 to 72 near the shore to around 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Tuesday: Mostly cloudy. Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 80 to 86 near the shore to around 66 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Lanai City

Today: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 75 to 84. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows around 68. East winds 10 to 20 mph.

Tuesday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 74 to 83. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Kaunakakai

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 90. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 61 to 74. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Breezy. Isolated showers in the morning. Highs 75 to 89. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Trade winds will remain gentle to moderate this week, delivering a few showers to windward areas. Winds will be light enough to allow afternoon sea breezes to bring some clouds and showers to leeward areas as well. Shower coverage and intensity may increase from Wednesday into Friday as moisture increases and the atmosphere becomes unstable. Light to moderate east to southeast winds are expected next weekend.

Discussion

Mid-level troughing NW of Kauai and a mid-level ridge extending over the Big Island from the E will prevail for the next couple of days, keeping modest instability over the W end of the islands chain. The trough will move SE over the islands as the ridge weakens from Wednesday through Friday, potentially leading to increased shower coverage and intensity. Trade winds will be gentle to moderate as weak low pressure systems far to the N will lie between the islands and relatively weak high pressure cells. While daily land/sea breezes can be expected over most leeward areas in this wind regime, there remains some uncertainty as to the amount of cloud and shower coverage the afternoon sea breeze circulation will generate the next couple of days.
Satellite shows few to scattered showery clouds moving W around 15 mph near the islands, while broken mid- and high-level clouds moving over Maui and the Big Island from the SW are gradually diminishing. Radar loop shows scattered showers, with a few heavy rain cores highlighting the modest atmospheric instability, also seen in the 12Z PHLI sounding. With the instabililty and very light winds over land this morning, leeward PoPs have been nudged upward for this afternoon. With surface pressure rises of 3-4 mb over the past 24 hours, the forecast expects the coverage and intensity of showers to be less than that of the last 2-3 days.
An increase in low-level moisture is forecast to arrive on the trade wind flow tonight and Tuesday, primarily affecting windward portions of Maui and Big Island with some increase in shower coverage. Latest guidance indicates this moisture will remain primarily limited to the lowest 10-12 thousand feet as the mid-level ridge builds. This modest moisture increase is currently seen between 150W and 153W, lending some credence to the model guidance. This moisture will also likely supply the other islands see a few windward showers.
From Wednesday into Friday, the mid-level trough NW of Kauai will move slowly SE over the islands, while low-level moisture gradually pools in the area as a low-level trough develops nearby. This combination of moisture and instability will increase chances for some locally heavy downpours, and potentially thunderstorms. Afternoon leeward sea breezes could be the strongest forcing for heavy shower development as trade winds weaken again, but some windward downpours appear possible as well. Light to moderate E-SE winds are projected for next weekend, with some decrease in shower coverage and intensity.

Aviation

An upper level trough just west of Hawaii will keep the air mass over the state moderately unstable. Weak trade wind flow in the lower levels will allow local sea breezes to predominate by day and land breezes at night.
As of 2 AM Monday, satellite and radar imagery indicated isolated to scattered light showers dotted across the smaller islands and windward Big Island. By late afternoon, showers will have increased in intensity and become focused over island interiors. VFR conditions will nevertheless prevail through at least early evening except for isolated MVFR CIG or VIS in showers.
The next significant band of trade wind showers is not expected to arrive until late this evening. Mountain obscuration could be an issue for windward Big Island late tonight or Tuesday morning.

Marine

The north to south pressure gradient down upon the islands will remain slack as surface high pressure does not establish itself to the north of the state until next weekend. This will result in several days of gentle to moderate trade winds with localized coastal daily sea breezes and weak overnight land breezes taking over.
A small, medium to long period south southwest swell will continue to build in through the day. This swell, in tandem with the arrival of a low, medium period southeast swell, has a High Surf Advisory in effect through 6 AM HST Tuesday. A small, medium period easterly swell from former Tropical Cyclone Kay will also move around the chain through Tuesday. The combination of these three swells will keep surf elevated along many southeast and east-facing shorelines into the middle of the week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for south facing shores of all islands.

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Data Courtesy of NOAA.gov