Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 67 near the shore to around 56 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 78. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 68. East winds 10 to 15 mph. Chance of rain 60 percent.

Friday: Partly sunny with scattered showers. Highs around 78. East winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows 56 to 61 in the valleys to around 50 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 71 to 78. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Lows 59 to 68. Southeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 71 to 78. Southeast winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows 57 to 69. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 71 to 78. East winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy east to east-southeast trades will prevail during the next couple days. Rainfall chances will remain highest over windward and mauka locations, particularly during the overnight and early morning hours, with afternoon showers possible over leeward areas each day. Increasing moisture and a return of breezy easterly trades will support greater windward shower coverage over the weekend through the middle of next week.

Discussion

Currently at the surface, a 1034 mb high is centered around 1250 miles north of Honolulu, while a 1002 mb low is positioned around 1050 miles west-northwest of Kauai. Moderate easterly trade winds prevail in unsheltered sections of the island chain early this morning. Infrared satellite imagery shows mostly cloudy conditions across much of the state. Radar imagery shows scattered to numerous showers moving into windward slopes and coasts, with quite a few decaying showers spilling into leeward communities. Main short term focus revolves around trade wind trends and rain chances during the next few days.
High pressure will strengthen as it remains nearly anchored well north of the islands today through Friday, while a low west- northwest of the state shifts northeastward to a location between 800 and 1000 miles northwest of Kauai. A slight strengthening of the trade winds is expected during this time, although they will generally hold at moderate to locally breezy levels. Due to the east-southeast boundary layer flow, some localized leeward sea breezes will be possible in the more sheltered leeward areas each afternoon as well. The low will weaken and eventually dampen into a trough over the weekend, while the strong high to the distant north settles southward and closer to the island chain. This will ramp the trades up to breezy levels statewide and shift the direction around to a more typical east-northeasterly direction. The strong high will hold north of the state early next week, before being reinforced by a new strong high to the distant north around the middle of next week. Breezy trades are expected to continue early next week, with windy conditions possible at times.
As for the remaining weather details, little change in the overall weather pattern is expected through Friday. Showers will favor windward slopes and coasts. Decaying showers will reach leeward communities at times, and a few leeward showers also developing each afternoon with the assistance of localized sea breezes.
There remains some uncertainty on how far east a front will make it late in the week, with the GFS remaining less progressive and further west than the ECMWF. This difference is impacting timing details on a shallow moisture boundary associated with an old front moving through the state Friday night and Saturday. Given the timing uncertainty, we will continue to advertise a typical trade wind weather pattern, with the expectation that a 6-12 hour period could be rather wet when this boundary moves through. Beyond that, fairly typical trade wind weather can be expected Saturday night through the middle of next week, with showers favoring windward and mauka areas and a few showers spilling leeward from time to time.

Aviation

Moderate trades will continue, with clouds and light showers favoring windward and mauka locations. MVFR CIGs/VSBYs will persist this morning for some windward areas, mainly in showers. Some of these showers are managing to spread into leeward sections of the smaller islands.
AIRMET Sierra is now in effect for mountain obscuration over north through southeast facing slopes of Kauai, and will likely continue through the morning hours today. Other windward locations may need to be included later this morning.

Marine

Fresh easterly trades develop tonight into Friday as high pressure builds over the islands in tandem with deepening low pressure northwest of the area. The Small Craft Advisory remains posted for the typical windier waters and will likely require expansion as winds continue strengthening into the weekend. Fresh trades continue well into next week.
The current moderate, long period NW swell peaked yesterday evening into last night and will now steadily subside through the remainder of the week. Another moderate, long period NW (330) swell is modeled to arrive early this weekend bringing similar surf to exposed shorelines. Surf may approach the advisory threshold during its peak late Saturday into Saturday night.
East-facing shores remain dominated by short period wind wave through the near term. However, deep low pressure descending from the Gulf of Alaska down the West Coast of the mainland US will generate a moderate, medium period NNE (060) swell that will fill in late this weekend and peak early next week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov