Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to around 72 above 3000 feet. East winds up to 25 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Isolated showers. Lows around 66 near the shore to around 55 above 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs around 84 near the shore to around 72 above 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 81. East winds 15 to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 67. East winds 15 to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs around 81. East winds 15 to 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with scattered showers. Highs 71 to 78 in the valleys to around 62 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 55 to 60 in the valleys to around 48 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 71 to 78 in the valleys to around 62 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs 74 to 84. East winds up to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 58 to 66. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 74 to 84. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 83. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 55 to 68. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 74 to 83. East winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will continue to strengthen through Friday as the high pressure ridge builds in north of the Hawaiian Islands. Easterly winds in the breezy to locally windy range are expected to last through the weekend. Passing showers are forecast through Sunday mainly over the windward and mountain areas, favoring the overnight to early morning hours. Leeward areas will see drier weather conditions. Trade wind speeds will decrease from Monday through Wednesday as a weakening cold front approaches the islands from the north. Shower trends will decrease as the frontal band stalls out north of the state and the ridge moves closer to the islands.

Discussion

This morning's satellite picture shows more stable stratocumulus just east of Hawaii drifting towards the islands on the trade winds. Trade wind speeds will strengthen through Friday as the subtropical ridge builds in north of the island chain. Local radar imagery this morning continues to show passing showers over eastern slopes of each island. Upper air balloon soundings from 2 AM HST this morning at Hilo and Lihue show trade wind temperature inversion heights around 7,000 to 9,000 feet. At this level clouds will be deep enough for scattered to numerous trade wind showers in the early morning hours over windward and mountain areas.
A strong high pressure system will remain in place north of the state through the weekend. Easterly trade winds will continue to blow across the region in the breezy to locally windy range into Sunday. Some wind favored areas over Maui and Hawaii Counties are approaching Wind Advisory thresholds today and may exceed these advisory thresholds from Friday to Saturday. Stability wise, temperature inversion heights will lower a bit today ranging from 6,000 to 8,000 feet. At this height passing showers over windward and mountain areas will remain in the forecast with lower shower activity over the typically drier leeward sections of each island.
Monday through Wednesday, the high pressure ridge moves closer to the islands and weakens as a weakening cold front approaches from the north. Long range guidance shows the forward motion of the frontal cloud band stalling out just north of the state by Wednesday with little impact on the precipitation side of the forecast. Expect decreasing trade wind speeds into the moderate range with more stable conditions as the ridge axis moves closer to the state. Shower activity will decrease into brief showers over windward areas, favoring the overnight to early morning hours.

Aviation

Easterly trade winds have increased overnight, and are expected to remain locally strong into Friday. The strongest winds will be over the eastern end of the state. VFR conditions are expected to prevail, with some brief MVFR conditions possible in passing clouds and showers over windward and mauka areas.
AIRMET Tango continues for mechanical turbulence to the lee of the mountains of Maui and the Big Island. Anticipate this being in effect through tonight. It may be expanded to additional islands later today.

Marine

High pressure north of the state will keep strong to near Gale force trade winds blowing through Saturday. A Small Craft Advisory (SCA) is now in effect for all coastal waters through 6 PM Friday. This SCA may need to be extended for all or portions of the marine area into the weekend. The trades could relax a bit Sunday and Monday as a decaying front shifts southward toward the islands.
The current medium period northwest swell will continue to gradually decline through Friday, with minimal surf then expected through the middle of next week.
The current long-period south swell is expected to gradually lower during the next few days, however a small reinforcement arriving tonight and Friday will help to keep south shore surf elevated into early next week. A High Surf Advisory (HSA) remains in effect for south facing shores through 6 pm this evening, and the HSA will likely be allowed to expire with the afternoon forecast package. Surf should drop below the summertime average along south facing shores Tuesday and Wednesday.
East shore surf should hold fairly steady at or slightly above seasonal levels through Saturday. A slight lowering of the trade wind speeds over and upstream of the islands will allow for a small decline in east shore surf Sunday and Monday. A slight boost will then be possible Tuesday and Wednesday as the trades ramp back up.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for all south facing shores.
Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters.

Data Courtesy of NOAA.gov