Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny. Isolated showers in the afternoon. Highs around 84 near the shore to around 72 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening, then scattered showers after midnight. Lows around 70 near the shore to around 59 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny with scattered showers. Highs around 83 near the shore to around 71 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Sunny with isolated showers. Highs around 81. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 66 to 71. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly sunny with scattered showers. Highs around 80. East winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers. Highs 71 to 78 in the valleys to around 62 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with showers after midnight. Lows 59 to 64 in the valleys to around 52 above 4000 feet. East winds up to 10 mph. Chance of rain 80 percent.

Monday: Partly sunny with numerous showers. Highs 70 to 77 in the valleys to around 61 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 74 to 84. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 62 to 70. Southeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Numerous showers. Highs 73 to 83. Southeast winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 74 to 83. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Lows 59 to 72. Northeast winds up to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 73 to 82. East winds up to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will prevail today. A band of deeper moisture will shift into the eastern islands this morning, then into the western end of the state tonight, bringing an increase in showers as it moves through. The trades will ease Monday through the middle of next week, allowing land and sea breezes to be common over the western islands with moderate east- southeast winds prevailing over the eastern end of the state. A closed low aloft could bring some unsettled weather with locally heavy rain and thunderstorms to portions of the state Tuesday and Wednesday. Breezy trade winds and more typical windward and mauka focused showers appear to return Thursday into next weekend.

Discussion

Currently at the surface, a 1032 mb high is centered around 1300 miles north-northeast of Honolulu, and a cold front is located roughly 1100 miles west-northwest of Kauai. The gradient remains rather tight, with moderate trade winds prevailing in unsheltered areas early this morning. Infrared satellite imagery shows mostly clear to partly cloudy conditions across most of the state, with a bit more cloud cover coming into windward sections of the Big Island. Radar imagery shows scattered showers moving into windward Big Island, isolated showers affecting windward sections of the smaller islands, and dry conditions in leeward locales. Main short term focus revolves around rain chances and trade wind trends during the next couple days.
High pressure northeast of the islands will keep moderate to locally breezy trade winds in place today. The trades will begin to ease tonight and Monday over the western islands as a cold front approaches from the northwest, while moderate to locally breezy trade persist over the eastern end of the state. The front will then weaken into a trough west of the islands Monday night through Wednesday, while the high to the northeast weakens. Winds will become light and variable over the western islands during this time, with land and sea breezes dominant. Over the eastern end of the state moderate east-southeast winds will prevail. The trough west of the state will dampen out Wednesday night and Thursday as high pressure builds north of the islands, bringing a return of moderate to locally breezy trade winds. The high will then strengthen slightly and settle southward Thursday night through next weekend, with breezy to locally windy trades expected.
As for the remaining weather details, a band of deeper moisture will move into windward sections of the eastern islands today, bringing an increase in showers here. Meanwhile, rather dry trade wind weather will prevail over the eastern end of the state. The airmass will remain somewhat unstable over the Big Island, so a thunderstorm or two will be possible this afternoon. The deeper moisture will then shift westward tonight and Monday, bringing an increase in showers to the western islands, while drier air works into the eastern end of the state bringing a reduction in shower coverage. A thunderstorm could pop once again Monday afternoon on the Big Island as the airmass will remain somewhat unstable.
The forecast becomes more interesting Monday night through the middle of the week, as a deep upper level trough closes off a southward moving mid/upper level low west of the state. Model guidance shows the potential for some deep moisture to be advected northward on the southeasterly boundary layer flow into the islands during this time, but differs on how close the closed low will be to the state. There is the potential for some heavy rainfall and thunderstorms, particularly over the western end of the island chain, but details remain uncertain at this time.
Although there remains some model differences during the late week into next weekend time frame, the general trend appears to favor a return to more typical trade wind weather across the island chain.

Aviation

This morning, expect isolated shower activity to mainly affect areas along the windward coasts and slopes with partly cloudy and dry conditions elsewhere. By this afternoon, however, isolated thunderstorms will become possible over the Big Island. Periods of MVFR ceilings and visibility may accompany these storms.
High pressure far northeast of the state will allow for moderate easterly flow to persist across the island chain during the forecast period.
No AIRMETs are currently in effect.

Marine

Trade winds will remain in the moderate to locally strong range today across the region. A Small Craft Advisory (SCA) was extended for the typically windy waters around Maui and the Big Island through 6 PM Monday. Wind speeds may weaken below SCA levels from Monday night through Wednesday as another cold front approaches the islands from the northwest. Moderate to locally strong trade winds return from Thursday into next weekend.
Small surf along the north and west facing shores will hold today from a small north-northwest (320-330 degree) swell. A moderate sized long period northwest (320 degree) swell will arrive Monday, peak Tuesday, then gradually lower Wednesday through Friday. This next swell will produce a large increase to north and west shore surf heights from late Monday through Wednesday, approaching High Surf Advisory (HSA) levels as the swell energy peaks on Tuesday.
Small surf along the south facing shores remains in the forecast today. A new long period south-southwest (200-210 degree) swell will build from Monday night to Tuesday, peaking Wednesday and Thursday near HSA levels. This swell energy will then gradually lower from Friday into next weekend.
Small surf along east facing shores will trend up slightly into Monday as the trades strengthen over and upstream of the islands. East shore surf will build close to seasonal average levels by the end of the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov