Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs around 85 near the shore to around 75 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly clear with isolated showers. Lows 66 to 71 near the shore to around 57 above 3000 feet. East winds 10 to 20 mph shifting to the northeast after midnight. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs around 84 near the shore to around 74 above 3000 feet. East winds 10 to 15 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs around 83. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly cloudy with scattered showers. Highs around 82. East winds around 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs around 78 in the valleys to around 67 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 60 in the valleys to around 52 above 4000 feet. East winds 15 to 25 mph. Chance of rain 50 percent.

Friday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 77 in the valleys to around 66 above 4000 feet. East winds 15 to 20 mph. Chance of rain 60 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 78 to 84. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 60 to 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 77 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 76 to 82. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 58 to 71. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 81. East winds 10 to 15 mph. Chance of rain 60 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will prevail through Friday. Low clouds and showers carried by the trades will remain focused across windward facing slopes. The trade winds may weaken slightly by Saturday, with an increase in shower activity possible this weekend. The trade winds are forecast to gradually strengthen again early next week.

Discussion

A 1027 mb surface high pressure system continues to meander near 32N 163W, or about 750 miles north-northwest of Lihue. The tight pressure gradient south of this feature is maintaining moderate to locally breezy trade winds across the state early this morning. Aloft, the axis of a westward moving upper-level trough is evident about 525 miles west-southwest of Lihue. The south-southwest flow along the eastern periphery of this feature continues to bring some thin cirrus clouds across the state. A mid-level ridge has also nosed in directly over most of the island chain, which has caused the atmosphere to become more stable overnight. The low- level trade wind inversion is between 5500 and 6500 feet based on the morning sounding profiles from Lihue and Hilo. Loops of satellite imagery show scattered to broken low clouds being transported by the low-level trade wind flow into the windward sides of most of the islands east of Kauai, while scattered low clouds are moving into Kauai. Radar reflectivity data indicate there are scattered light showers embedded within some of these low clouds, especially near Oahu, Maui, and the Big Island.
The forecast guidance indicates the relatively stable trade wind weather pattern will likely prevail through Friday, as the mid- level ridge continues to exert its influence over the state. The westward moving upper-level trough may also transport some thin cirrus clouds across the area. The surface high pressure system will remain far north of the region, which will keep moderate to locally breezy trade winds in place. The trade winds will continue to deliver low clouds and brief showers into the windward sections of the islands. The low-level trade wind flow may be strong enough to carry a few light showers over to leeward sections of some the smaller islands, especially during the late night / early morning hours, but expect mostly dry conditions to prevail. In addition, clouds and showers may develop along upslope sections of the leeward Big Island each afternoon.
By Saturday, a surface front pushing in from the northwest will likely begin to weaken the surface high pressure system to the north of the region. This is expected to cause the trade winds to weaken slightly this weekend. The forecast models suggest that an upper-level trough, which is associated with the surface front, may dig down toward the state from the north. Assuming this scenario unfolds as depicted by the guidance, the weakening frontal boundary may move down closer to the island chain by early next week. The decrease in atmospheric stability due to the nearby trough aloft combined with moisture ahead of the frontal boundary may cause an increase in low clouds and trade showers. At the same time, a new surface high building far northwest of the region is expected to cause the trade winds to gradually strengthen next week. A weak mid-level ridge may move over the state by Tuesday, which would tend to cause the atmospheric stability to increase, so no heavy rainfall is anticipated at this time.

Aviation

High pressure northeast of the state will keep moderate to breezy trade winds in place for the next few days. Passing showers will favor windward slopes and coasts. Total rainfall will be light.
A strong subtropical jet over the area will bring widespread high clouds and turbulence. AIRMET Tango remains in effect for moderate upper level turbulence over the entire state and will likely remain in place through today. AIRMET Tango is also in place for moderate low level turbulence over and downwind of island terrain due to breezy trade winds.

Marine

Fresh to strong easterly trade winds will continue through next week as the ridge remains anchored to the north. The ridge is forecast to shift southward Friday into the weekend and weaken slightly, but this will be brief. Guidance shows the ridge building north of the state behind a front Sunday through early next week, which will translate to strong easterly trades for most waters Sunday night through the first half of next week. If this materializes, the Small Craft Advisory will need to be expanded to most waters by Monday.
Surf along east facing shores will remain rough and choppy each day through next week. Heights may briefly ease Friday into the weekend due to the aforementioned weakening of the ridge/winds. An increasing trend is likely through the first half of next week as strong trades expand over most waters and far upstream across the eastern Pacific.
Small surf is anticipated for north and west facing shores through the weekend, with the exception of some trade wind energy wrapping into exposed northern shores. For the extended, there is a potential for a short/medium-period northerly swell arriving early next week and lingering through midweek.
Surf along south facing shores will remain small with mainly background energy rolling through occasionally.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov