Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny in the morning, then partly sunny with isolated 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 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 64 to 69 near the shore to around 55 above 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 83 near the shore to around 73 above 3000 feet. Light winds. Chance of rain 40 percent.

South Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 81. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 62 to 68. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 81. Light winds. Chance of rain 30 percent.

Kaua’i Mountains

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 76 in the valleys to around 65 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 58 in the valleys to around 50 above 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny. Scattered showers in the afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 40 percent.

North Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 76 to 82. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 58 to 67. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny. Scattered showers in the afternoon. Highs 76 to 82. Light winds. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny with isolated showers. Highs 74 to 80. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 56 to 69. Light winds. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 80. Light winds. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A rather dry pattern will continue across the state today through Monday night, while the trade winds gradually ease and shift southeasterly. A front will stall out west of Kauai Tuesday through Thursday, bringing an increase in south to southeast winds to the state. The southerly flow will bring an increase in moisture and the potential for some heavier showers and even a few thunderstorms, particularly over the western islands. Trade winds and a more typical windward and mauka shower pattern appears to return for the end of the work week and into next weekend.

Discussion

Currently at the surface, a cold front is located around 400 miles northwest of Kauai, while a ridge of high pressure is positioned around 400 miles north-northeast of Honolulu. The resulting pressure gradient is producing moderate trade winds in unsheltered areas early this morning. Infrared satellite imagery shows mostly clear to partly cloudy conditions, with a bit more cloud coverage in some windward locales. Radar imagery shows very little shower activity, with only a few very light showers or sprinkles affecting windward slopes and coasts. Main short term focus continues to revolve around trade wind trends and rain chances.
The trades will ease over the western islands this afternoon as the cold front edges closer to the state, allowing some localized sea breezes to develop in the more sheltered areas. Meanwhile moderate trades will continue over the eastern islands. Not much change to the wind forecast is expected tonight and Monday, with land and sea breezes common over the western islands and moderate trades prevailing over the eastern end of the state. The front will move a bit closer to the islands Tuesday, then stall out west of Kauai Wednesday and Thursday. This will bring moderate south to southeast winds to the island chain. Trade winds then appear to return for the end of the work week into next weekend as ridging builds in north of the state.
As for the remaining weather details, rather dry weather will continue today through Monday night, with limited shower activity favoring windward areas at night and in the morning, and localized sea breezes assisting with the development of a few interior and leeward showers each afternoon. Additionally, lingering mid-level instability may allow a thunderstorm to pop each afternoon over the Big Island slopes.
There remains some uncertainty in the mid week forecast as model guidance has shown poor run to run continuity. Overall however, guidance continues to depict an increase in deep moisture as the low level boundary layer flow tips south and southeast, which should bring an increase in shower activity particularly to the western islands Tuesday through Thursday. A more unstable airmass is also expected over the islands during this time, which could produce some heavier showers and even a few thunderstorms. A more typical trade wind pattern then appears to return Friday into next weekend.

Aviation

A weak high pressure ridge north of the Hawaiian Islands will keep light to moderate east to southeast winds blowing across the region into Monday. Large scale winds will be light enough for sea breezes during the day along the western sides of each island. Clouds will build over each island in the afternoon hours with isolated to scattered showers. Overnight land breezes will clear out most of the cloud cover a few hours after sunset. Isolated thunderstorms remain in the forecast for this afternoon near the Big Island.
No AIRMETs in effect and none are expected until later this afternoon where additional mountain obscuration AIRMETs are possible.

Marine

Surface high pressure far northeast of the state, located off the U.S. Pacific NW coast, is producing a tight enough pressure gradient back toward the islands to maintain moderate to locally strong regional trade winds. A Small Craft Advisory (SCA) is in effect for the windier zones surrounding Maui County and Big Island through this afternoon to account for locally strong trades channeling around the eastern islands. An approaching low and associated front from the northwest will lift north of the offshore waters the next couple of days. As this low lifts north, its trailing front will enter the western offshore waters. This front will not only increase thunderstorm activity over the west offshore waters but will also veer moderate winds more southeasterly, likely transitioning breezes to light and variable around Kauai by Monday. The low may become stationary northwest of the islands and stall the front in the vicinity of the western nearshore waters late Monday. This more static pattern will maintain moderate east to southeast winds across the eastern half of the state while holding light and variable breezes over the western waters through the remainder of the week.
A small, medium period northwest swell (310 degree) is expected to arrive this afternoon and should be arriving at the far northwest buoys before sunrise. This swell will provide a boost in surf along north and west-facing shores through Monday. This swell will slowly decline late Monday and be gone by Wednesday. A series of smaller northwest to north swells are expected to pass through during the second half of next week. Surf along east-facing shores will experience a minor boost today as trades strengthen over and upstream of the islands. Although trades will slightly weaken over the state early next week, a persistent moderate trade fetch upstream of the area should result in a continued east shore, short period wind wave chop through next week. Other than very small early to mid week bumps along southwest and southeast exposures from low period energy moving in from the Southern Hemisphere and within the trade belt, respectively, surf along many south-facing shores will remain small through the week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov