Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny. Isolated showers in the afternoon. Highs around 85 near the shore to around 75 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 71 near the shore to around 57 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 83 near the shore to around 73 above 3000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny. Isolated showers in the morning. Highs around 83. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 64 to 70. East winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81. East winds up to 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny. Scattered showers in the afternoon. Highs around 78 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Lows around 60 in the valleys to around 52 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs around 76 in the valleys to around 65 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with isolated showers. Highs 78 to 84. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 60 to 69. Southeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Partly sunny with scattered showers. Highs 76 to 82. Southeast winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with isolated showers. Highs 76 to 82. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 58 to 71. East winds up to 15 mph. Chance of rain 40 percent.

Sunday: Partly sunny with scattered showers. Highs 74 to 80. East winds up to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Strengthening trade winds will bring more settled weather and lower humidity today, with just a few mainly windward showers expected. Winds will shift southeast late Sunday and Monday, but a mostly dry weather regime will continue. A slow-moving front will bring the potential for increased showers late Tuesday, with increasingly unsettled weather possible Wednesday and Thursday as a moist southerly flow develops across the island chain. Trade winds could return for the end of the upcoming work week.

Discussion

Currently at the surface, a cold front is located around 800 miles west-northwest of Kauai, while a high pressure ridge axis is positioned around 300 miles north of Lihue. The pressure gradient has strengthened a bit overnight, with light to moderate trade winds now in place in unsheltered areas. Infrared satellite imagery shows broken cirrus moving overhead along with some low clouds drifting into windward areas mainly over the eastern end of the state. Radar imagery shows scattered showers moving into windward sections of the Big Island and Maui, with little if any shower activity elsewhere. Main short term focus revolves around trade wind trends and rain chances.
A building ridge north and northeast of the state will allow the trade winds to strengthen today, then persist at moderate to levels through Sunday. The trades will begin to ease late Sunday and Sunday night over the western islands as a cold front edges closer. The front is forecast to stall out just west of the state early next week, with light winds allowing for land and sea breezes over the western islands, while moderate southeasterly winds prevail over the eastern end of the state. The forecast becomes more uncertain during the middle to latter part of next week, with the 00Z model solutions suggesting a wave may develop along the stalled front west of the islands. If this pans out, we could see an increase in southerly winds across the island chain Wednesday and Thursday, with trade winds perhaps returning for the end of the upcoming work week.
As for the remaining weather details, a building low and mid level ridge should keep a fairly dry pattern in place during the next several days. Limited shower activity will favor windward slopes and coasts with the returning trades, although we could see an isolated shower each afternoon due to localized sea breezes in the more sheltered leeward areas. Additionally, a thunderstorm could pop each afternoon through the weekend over the Big Island slopes due to lingering instability aloft. A more typical land and sea breeze pattern will set up early next week. Rather dry conditions should continue Monday, with a few showers possible over the island interiors during the afternoon and near the coast at night. The airmass moistens up Tuesday, so we should see an increase in shower coverage across the islands. The forecast becomes more interesting and uncertain during the middle to latter part of next week. Both the GFS and ECWMF suggest we could get into a moist southerly flow with the potential for some heavy rainfall and possibly even thunderstorms.

Aviation

Two low pressure systems north and northwest of the state will continue to keep the high pressure ridge north of the islands in a weakened state with light to moderate east to southeast winds blowing across the Hawaii region into Sunday. Large scale wind speeds are light enough to allow sea breezes to develop each day over the terrain sheltered western slopes of each island. Brief showers are possible. Isolated thunderstorms may develop near the Big Island this afternoon.
No AIRMETs are currently in effect.

Marine

A ridge will fill in behind an exiting upper trough north of the state this morning. This will support primarily stable weekend conditions and maintain low chances for just isolated showers. The pressure gradient from surface high pressure located far northeast of the islands will produce moderate to locally strong east trade winds this weekend. A Small Craft Advisory (SCA) will be in effect for the windier zones surrounding Maui County and Big Island from this afternoon (12 PM HST) through Sunday afternoon to account for strengthened easterlies through these zones. An approaching low from the northwest the next few days will lift north of the offshore waters Monday. As the low lifts north, its associated surface trough will enter the west waters. This will veer gentle to moderate breezes more southeasterly and possibly transition breezes to light and variable around Kauai by the middle of next week. Northwest Pacific energy diving southeastward behind this trough will assist in moving the surface boundary closer to the waters Thursday and ultimately veering late week moderate winds more southerly.
Lingering small, medium period northwest swells will hold small surf along north and west-facing shores through the day. A slightly larger, longer period northwest swell will build in Sunday afternoon. This will provide a small boost to north and west shore surf from Sunday night into Monday. This swell will begin falling Tuesday with only small surf expected by Wednesday. A similar size, medium period northwest swell will result in a slight boost to north and west-facing shore surf late next week. Surf along east-facing shores will hold steady through tonight with a minor boost expected over the weekend as trades strengthen over and upstream of the islands. Several days of this moderate east fetch will result in little change to east chop through next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory from noon today to 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov