Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. 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. Lows around 68 near the shore to around 57 above 3000 feet. Northeast winds up to 15 mph.

Sunday: Mostly sunny. Isolated showers in the afternoon. Highs around 83 near the shore to around 71 above 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs around 83. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly clear with isolated showers. Lows 64 to 69. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 82. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 79 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Partly cloudy with scattered showers. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Sunday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 70 to 78 in the valleys to around 65 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 76 to 83. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 60 to 69. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs 75 to 82. Southeast winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly cloudy in the morning then becoming mostly sunny. Scattered showers. Highs 76 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 58 to 70. Northeast winds around 10 mph. Chance of rain 20 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 75 to 82. East winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Locally breezy trade winds will persist today before trending down Sunday as a front begins to approach from the northwest. A kona low will develop far northwest of the islands on Monday, move southward toward the islands Monday night into Tuesday morning, then shift west away from the state thereafter. This large low will shift winds around to the south Monday, bringing deeper moisture up over the islands and periods of muggy, rainy weather to portions of the state during the first half of next week. Breezy to windy trades and more typical weather should make a return for the end of the upcoming work week.

Discussion

Currently at the surface, a ridge of high pressure is positioned around 600 miles north of Honolulu, while a nearly stationary front is located around 650 miles west-northwest of Kauai. The resulting gradient is producing light to moderate trade winds across the island chain early this morning, with land breezes present in some of the more sheltered leeward locales. Infrared satellite imagery loop shows a decrease in cloud coverage during the past couple hours, although mostly cloudy conditions prevail in most areas. Radar imagery shows numerous showers affecting windward slopes and coasts, with some of these showers reaching leeward areas as well. Main short term focus revolves around rain chances and trade wind trends.
The band of low clouds and showers will keep some showery weather in place over windward areas early this morning, with a shower or two reaching leeward locales as well. As the band of clouds and showers exits late this morning, drier conditions will overspread the state, and the trade winds will strengthen to moderate to locally breezy levels. A dry trade wind pattern with limited showers is expected to prevail through the remainder of the weekend, with moderate to locally breezy trade winds holding in place through the early Sunday, before easing off Sunday afternoon as a front approaches from the northwest. The winds will shift around to the southeast and south Sunday night, with fairly dry weather conditions continuing and showers limited primarily to windward areas of the eastern islands.
Model solutions continue to show some significant differences during the early to middle part of next week, but they both agree that a deep layered kona low will develop around 400-500 miles northwest of Kauai Monday, before retrograding westward Tuesday and Wednesday. An approaching front will shift winds around to the south on Monday at moderate speeds, allowing some deep tropical moisture to lift northward into Kauai and Oahu, while drier conditions persist over Maui County and the Big Island. The big question is how much eastward progress the front will make before it stalls out and shifts back west as a trough. For now there remains quite a bit of uncertainty, with the GFS being the wetter model and the most aggressive with the eastward progression of the front, while the ECMWF is drier and keeps the front further to the west. For now will show a continued southerly flow at moderate speeds through Tuesday, with trade winds returning and becoming breezy on Wednesday. The highest rain chances appear to focus over the western islands at the moment, but given the model differences, details remain shaky at the moment. There remains the potential for some heavy rain and even thunderstorms in association with this frontal band, but will hold off on adding this to the forecast until details become more clear.
Guidance suggests that a strong high will build northeast of the islands during the middle to latter part of next week, bringing a return of more typical weather with breezy to windy trades.

Aviation

Moderate easterly trades will persist through the remainder this morning and into the afternoon. A slightly drier airmass will advect into the region today and limit scattered shower activity to mainly windward locations. Brief MVFR ceilings and visibility may occur with this activity, though not expecting anything widespread. Isolated showers expected elsewhere.
AIRMET SIERRA remains in effect above 2500 feet for north thru east portions of Kauai, Oahu, and Maui due to mountain obscuration resulting from reduced visibility and ceilings in clouds and showers.

Marine

Surface high pressure northeast of the state will maintain a moderate easterly trade flow across the Hawaiian nearshore waters this weekend. Sunday night through Monday's winds will veer to the southeast and strengthen as a strong cold front approaches the islands from the northwest Sunday into early next week. A gale force low is expected to develop along this front early Monday morning. This deepening low will wobble west away from the local waters and veer moderate winds more south Monday into Tuesday. Fresh to strong Small Craft Advisory to localized Gale Warning level easterlies may occur late in the week as the low moves off to the northwest and high pressure builds in from the northeast.
All three of the north shore buoys (Hanalei, Waimea Bay and Hilo) are observing a steady decline of this most recent large, long period west northwest swell. 6 foot or under medium period swell signals that surf has fallen below High Surf Advisory (HSA) criteria along the north and west-facing shores. Therefore, the HSA has been allowed to expire this morning. A moderate size, medium period northeast swell (30-40 degree) is expected to fill in through the day. This swell may peak this evening's surf to near or slightly below HSA heights along some north and east- facing shores before slowly subsiding into early next week. Gale to near storm force winds along the backside of a vicinity gale low northwest of the area early next week may generate and send a large, medium period northwest swell into our coastal waters. This could easily lift north and west-facing shore surf back to HSA heights on Tuesday.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov