Photo Credit: Braden Jarvis

West Kaua’i

Today: Sunny. Isolated showers early in the morning. Highs around 87 near the shore to around 75 above 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows 66 to 71 near the shore to around 57 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 87 near the shore to around 75 above 3000 feet. Northeast winds up to 10 mph in the morning becoming light. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny with isolated showers. Highs 83 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 64 to 69. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs 83 to 88. East winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs 74 to 81 in the valleys to around 65 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Lows 57 to 63 in the valleys to around 54 above 4000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Sunday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 74 to 81 in the valleys to around 65 above 4000 feet. Northeast winds around 10 mph. Chance of rain 40 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 77 to 85. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 61 to 69. Southeast winds up to 10 mph. Chance of rain 30 percent.

Sunday: Mostly sunny with isolated showers. Highs 78 to 86. Northeast winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs 76 to 85. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 30 percent.

Tonight: Partly cloudy with scattered showers. Lows 59 to 71. North winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 30 percent.

Sunday: Mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs 76 to 85. East winds around 10 mph. Chance of rain 30 percent.

Detailed Forecast

Synopsis

Expect more stable conditions with drying trends today and tomorrow as unsettled weather conditions are diminishing this morning. Drier light to moderate trade winds will continue on Sunday. Trade winds will weaken into a variable sea breeze pattern on Monday and Tuesday as a low pressure system sets up far north of the state. A weakening cold front will then drift south through the islands, producing another round of slow moving showers across the state from Wednesday through Friday.

Discussion

Satellite and local radar imagery this morning already shows drying trends as an unsettled cloud band that brought overnight showers to most of the islands has drifted south of the state. Clouds and scattered shower activity lingers over the islands of Maui and the Big Island. This unsettled weather will diminish a later this morning.
Drier and more stable conditions are moving into the region on moderate northeasterly trade winds today. These moderate trades will be short lived as the subtropical ridge north of the islands weakens from Sunday through Tuesday, due to an approaching low pressure system far to the north. Expect light and variable winds on Monday and Tuesday with local scale sea breezes forming in the late morning hours, building clouds over mountains and island interior sections during the day. A high pressure ridge in the upper levels will keep fairly stable weather conditions in place with a low trade wind inversion heights capping vertical cloud development and therefore limiting shower activity.
By Wednesday the longer range guidance suggests a pattern change back to the wetter side, lasting through Friday. A low pressure system far north of the state will drop south, and cut itself off from the mid-latitude polar jet stream. A weakening cold front assoicated with this low will dive southward into the islands, driven by breezy northerly low level winds behind the front. Wet weather is expected as the clouds and showers along the frontal band pass through each island on Wednesday and Thursday. The current consensus of model runs shows the forward motion of this front stalling out near Maui by Thursday morning with the frontal band weakening into a trough. This low level trough will then drift westward as the parent low to the north also moves west. Another round of wet weather will spread back to the western islands of Oahu and Kauai from Thursday to Friday as clouds along this trough pass through both islands.
These cut off lows are very challenging for long range model solutions to predict in the five to seven day forecast window. This means there are some rather large differences between the predicted weather conditions late next week. These errors are not unusual and are minimized by using a model blend approach. However, this also means we may see large changes in our island by island weather impacts for this time period. Stay tuned for changes to our extended range forecast over the next few days as the weather prediction time line grows shorter and our confidence improves.

Aviation

High pressure building in from the northwest will usher in cooler, drier air. Light to locally moderate trade winds are expected across the smaller islands by tomorrow afternoon and windward Big Island by Sunday afternoon. The air mass across the state is becoming increasingly stable, but lingering moisture persists over the eastern end of the state. AIRMET Sierra for mountain obscuration remains in effect for windward portions of Maui and may need to be expanded to include windward Big Island Hilo northward. Conditions are expected to improve shortly after sunrise.
Later today, light sea breezes along the south and west facing coasts of the Big Island will drive weak cumulus buildups over the island's interior. Brief MVFR conditions possible in moderate showers along leeward slopes in the late afternoon and early evening hours.

Marine

Gentle to moderate north to northeast breezes today behind a weakening boundary that is hanging up and becoming more diffuse south of the Hawaiian Islands. Gentle to moderate trades will veer more easterly early next week as high pressure far northwest of the state moves east toward the region. This will result in weakened light to gentle easterlies through Tuesday. A cold front may reach the Kauai windward waters on Wednesday. Fresh to strong northeasterlies will occur in this front's wake and persist into Wednesday evening.
The north swell that peaked yesterday afternoon has traveled down the island chain. Early morning observations of between 7 to 8 feet medium period swell at Hilo's nearshore buoy indicate that a High Surf Advisory (HSA) is also warranted for the north-facing shores of Big Island through at least the early part of the day. The HSA will remain in effect for the north-facing shores of the smaller islands, except Lanai, through 6 PM HST today. Additionally, a Small Craft Advisory for elevated seas exposed to this north swell is in effect for the windward waters of Kauai, Oahu, and Maui County and Big Island through 6 PM HST today. The next similar size north northwest swell is scheduled to arrive around Kauai mid to late Sunday morning. This swell may potentially produce another round of near advisory level surf along north- facing shores as it peaks Monday. A larger north swell is modeled to reach our waters during the middle of next week. A small, medium period south swell will continue to provide a minor boost to south-facing shore surf through the day, before returning to background levels from Sunday through early next week. Except for eastern shores exposed to the north swell, east-facing shore chop will remain small the next several days as a result of anemic trades over and upstream of the islands.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for all exposed north facing shores.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters.

Data Courtesy of NOAA.gov