Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers. Highs 86 to 91 near the shore to around 76 above 3000 feet. East winds up to 10 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 72 near the shore to around 62 above 3000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs around 89 near the shore to around 78 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 82 to 90. East winds around 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 74. Northeast winds around 10 mph in the evening becoming light. Chance of rain 40 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 90. Light winds becoming east around 10 mph in the afternoon. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 75 to 84 in the valleys to around 66 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 71 in the valleys to around 59 above 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 76 to 86 in the valleys to around 67 above 4000 feet. Light winds becoming southeast up to 10 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 77 to 89. East winds up to 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 73. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 40 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 78 to 89. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 87. East winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 76. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 88. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Gentle to localized sea breezes will be the dominant wind pattern today. There will be an increase in overall shower coverage the next couple of days, especially across windward Big Island and Maui zones as an upper level low northeast of the state pulls a moist southern air mass across the islands. Drier conditions and strengthening trades are forecast this weekend.

Discussion

Hawaii remains under weak upper level ridging. A mid to upper level low about 450 miles northeast of Hilo will travel to the northwest through the day and pull its associated trough toward the state. This trough will tap into a more moisture rich southern air mass and drag this moisture across the state the next few days. The result will be cloudier skies, lighter winds, higher humidities and more frequent showers from this morning through Saturday.
The proximity of the upper level low and trough, with the accompanying plume of higher moisture, will likely enhance overnight precipitation with the highest rainfall impacting Big Island and Maui's windward communities. As mid level troughing advances northwest across the island chain through Friday, more statewide thicker clouds and an enhanced shower pattern can be expected the next couple of days. Large scale upper troughing and surface cold front moving east to the north of the islands will push the surface high (currently around 1,500 miles northeast of the area) further away from the region. This will slacken the upstream pressure gradient and ultimately weaken trades to gentle to low end moderate magnitudes Thursday through Friday. Localized daytime sea breezes and nocturnal mountain drainage winds will be more dominant within this lighter synoptic-scale wind regime. These smaller scale breezes will introduce daytime interior mauka and better sheltered area cloud buildup, along with more areal shower coverage, the next couple of afternoons. A large near-1040 mb North Pacific surface high will build in behind this weekend's frontal passage. This will reestablish and tighten the regional pressure gradient and restrengthen trades to more solid moderate to locally fresh speeds this weekend (Sunday). Drier air filtering in the wake of the trough's northern passage will lower weekend rain chances. A 'wash-rinse-repeat' pattern comes to fruition going into the middle of next week. Periods of higher moisture embedded within anchored regional trade flow through the middle of next week will fortify this idea of a more healthy dose of periodic windward and higher terrain-rooted shower activity. In the extended, a large gale low moving onshore across the mainland Pacific Northwest states may provide enough energy behind its accompanying cold front to push the boundary into our northern offshore waters next Thursday. Other than increasing north-facing shore rain chances, easterlies may veer southeast as the front washes out in the vicinity of the state Friday.

Aviation

Light to moderate trades are expected today, with the winds likely being light enough for sea breezes to develop in the more sheltered leeward areas. Low clouds and showers will favor windward slopes and coasts during the next 24 hours, with an area of enhanced moisture bringing a bit more showery weather and a better chance for some reduced CIGS/VSBYS to windward sections of the Big Island and possibly east Maui today.
AIRMET Sierra may be needed for mountain obscuration across windward sections of the Big Island later this morning.

Marine

Fresh to strong easterly trades will gradually ease through Friday as a weakness forms in the ridge to the north. While light and variable winds may develop over the Oahu and Kauai waters later tonight into Friday, fresh to strong trades will persist over the eastern end of the state. As a result, the Small Craft Advisory has been extended over the windier waters and channels around Maui County and the Big Island through the day. Fresh to locally strong easterly trades will return over the weekend, then weaken again early next week as broad gales form far northwest and northeast of the state.
Surf along north-facing shores will steadily fade through the second half of the week as a north-northwest swell moves out. A small, medium-period pulse is possible over the weekend and into early next week, which should be enough to prevent the surf from going flat. An upward trend is possible late next week due to the aforementioned gale forming northeast of the state from Monday through midweek.
Surf along south-facing shores will remain small, with mainly a mix of short to medium period south southeast and south southwest swells moving through. The next small, long period southwest swell is expected over the weekend, with a similar pulse arriving early next week.
Surf along east-facing shores will remain small and choppy each day through the weekend, then trend down as the trades ease locally and upstream early next week.
Peak monthly tides could lead to minor coastal flooding in the typical low-lying vulnerable areas around or just before daybreak each day through the weekend, beginning on Friday morning.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov