Photo Credit: Jason Weingardt

West Kaua’i

Today: Sunny. Scattered showers in the morning. Highs 87 to 92 near the shore to around 78 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly clear. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph.

Sunday: Sunny. Isolated showers in the afternoon. Highs 86 to 93 near the shore to around 78 above 3000 feet. Northeast winds up to 10 mph shifting to the south in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 86 to 92. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 71 to 76. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 85 to 92. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 87 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 71 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 75 to 86 in the valleys to around 68 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 78 to 89. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows 66 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 89. East winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Today: Breezy. Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 76 to 89. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 79. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 89. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Expect moderate to locally breezy trade winds to continue through tonight with passing showers through the early morning hours as a weak low level trough passes through the western half of the state. Trade wind speeds will drop rapidly on Sunday and become light from Monday through Tuesday. These lighter large scale winds will allow local scale land and sea breeze coverage to expand. Converging sea breeze winds may produce slow moving scattered afternoon showers over island interior sections on Monday and Tuesday. A slow strengthening in the trade winds remains in the forecast from Wednesday through Friday.

Discussion

This mornings infra-red satellite imagery shows more stable clouds up stream of the islands as the low level trough moves westward away from the state. Shower trends will decrease later this morning as more stable conditions return. Trade wind temperature inversion heights remain in the 6,000 to 8,000 foot elevation level as shown in this mornings 12Z (2 AM HST) upper air balloon soundings at Lihue and Hilo. A short wave ridge moving into the region should decrease inversion heights today, decreasing shower trends later this morning.
A high pressure system far north of the Hawaii Region will slowly weaken today as deepening upper lows north of the state begin to erode the ridge north of the islands. Expect a sharp decrease in trade wind speeds starting on Sunday and lasting through Tuesday as surface troughs develop north of the island chain, surface reflections of these upper lows. As large scale trade winds diminish, local scale island and ocean heating differences will drive the expansion of overnight land and daytime sea breezes. Trade winds will slowly build back into the region from Wednesday through Friday. A lingering trough pattern just north of the Hawaiian Islands will slow the trade wind speed trends over the second half of next week.
The weather pattern changes starting on Sunday as we transition from trade winds to afternoon sea breezes. Instead of windward and mountain showers during the overnight to early morning hours, we will shift to converging sea breeze winds, island heating and troughing aloft combining forces to produce clouds and slow moving scattered showers over island interior sections each afternoon. As we transition back to trade winds from Wednesday through Friday, sea breeze areas will shrink in coverage to the more terrain sheltered western slopes and shower activity will shift to more isolated interior showers in the afternoon with scattered overnight to early morning showers over windward and mountain areas.

Aviation

Trade winds will be moderate to locally breezy today and then gradually weaken Sunday through Tuesday. Clouds and showers will continue to favor windward and mauka areas through the morning hours today, which may bring brief periods of MVFR conditions to these areas. Otherwise, VFR conditions will generally prevail.
AIRMET Tango for mountain lee turbulence remains in effect for the leeward portions of Molokai, Oahu and Kauai, but will likely need to be dropped later this morning or afternoon due to weaker winds.
With the weakening winds Sunday through Tuesday, cloud and shower coverage will likely begin to take on a more land/sea breeze regime with offshore winds overnight and clouds and showers forming across convergent boundaries over inland and mauka locations during the day.

Marine

A strong surface high pressure ridge positioned far north of the state and will help maintain fresh to locally strong trade winds through tonight. As a result, a Small Craft Advisory (SCA) remains in effect for the normally windier zones around Maui County and the Big Island. On Sunday, winds will veer to the southeast and weaken as a trough of low pressure passes north of the area. Light to gentle breezes will continue through mid next week.
The breezy trades will maintain rough, choppy surf along the east-facing shores today. A longer period NE swell (around 10 seconds), associated with former Tropical Cyclone Irwin, is also mixed in. However, peak east shore surf should remain below the 10 ft High Surf Advisory (HSA) threshold. East shore surf is expected to trend lower on Sunday and into early next week as the trades weaken.
South shore surf should remain small through Sunday. A moderate (3 to 4 foot) south to south-southwest swell is expected to slowly fill in Monday and peak from Tuesday through Wednesday near HSA levels, then slowly decline through rest of the week.
For the north and west facing shores, surf is expected to increase today as a swell generated by a storm-force low (former Tropical Cyclone Damrey) arrives. This swell is forecast to come in from the northwest (310 degrees), then gradually transition over to north-northwest (340 degrees) by early next week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov