Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny with scattered showers. Highs around 81 near the shore to around 71 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 68 near the shore to around 57 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to around 71 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 80. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

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

Monday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 80. Northeast winds around 15 mph. Chance of rain 60 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Showers in the morning, then numerous showers in the afternoon. Highs 69 to 75 in the valleys to around 64 above 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 61 in the valleys to around 53 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 75 in the valleys to around 64 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 60 percent.

North Kaua’i

Today: Mostly cloudy with numerous showers. Highs 71 to 80. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 71 to 80. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Breezy. Mostly cloudy with numerous showers. Highs 71 to 81. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 71 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The trade winds will shift slightly this week, blowing from a more east-northeast direction and decreasing in strength slightly through Tuesday. Trade wind directions will shift from the east by Wednesday as an approaching cold front north of the state will flatten the ridge far north of the islands. Weather conditions in this pattern will feel like typical trade winds for most for the next seven days. Cloud bands moving through the trade winds will bring periods of passing showers to windward and mountain areas, mainly in the overnight to early morning hours.

Discussion

In the satellite imagery this morning we see a similar pattern with unstable cloud bands moving into the islands in the trade wind flow. A low pressure system remains in place northeast of the state, a high pressure system lingers far north of the islands, and a cold front far to the northwest is slowly approaching the region. A deeper band of clouds and showers remains focused over Kauai and the Kauai Channel this morning. This band will slowly drift eastward spreading enhanced showers to Oahu and Maui County later tonight. Local doppler radar also shows numerous showers forming as these unstable cloud bands move into the windward slopes of each island, expect these passing showers to continue through the early morning hours and then diminish in coverage by mid-morning. A few of these stronger showers may reach the typically drier leeward areas.
The weather pattern this week continues to show trade winds with slightly different wind speeds and directions. The high pressure ridge north of the state will drift south and flatten out due to an approaching cold front far northwest of the region. This shift in the ridge location will cause wind speeds to decrease over the islands and wind directions to shift from a more east-northeasterly direction through Tuesday. Trade wind speeds are less certain for next weekend as forecast guidance continues to differ on placement and intensity of the high pressure system north of the region.
Weather conditions in this pattern will feel like typical trades with passing showers mainly affecting windward and mountain areas of each island. Drier leeward sections may see brief isolated showers. One wrinkle in the forecast is associated with a long band of unstable clouds currently near Kauai that will slowly drift eastward across Oahu and Maui County, this band of clouds will enhance shower activity across the islands of Oahu, Molokai and Maui later tonight through early Monday morning. On Wednesday the approaching cold front will stall north of the state and then dissipate, producing no impact on island rainfall. The highest chances for showers in this pattern will occur over windward and mountain areas of each island during the typical overnight to early morning hours.

Aviation

Winds continue to be a touch stronger over the northern islands early this morning, but expecting winds overall to be a little lower than yesterday. Kauai and Oahu remain under AIRMET Tango for moderate low level turbulence to the lee of the mountains. As long as winds continue to decline some today, this AIRMET will likely be cancelled later today.
Clouds and showers continue to ride in on the trade winds. The radar over the last few hours has shown an uptick in shower activity. Satellite shows an uptick in clouds over the central islands. Conditions appear to be improving some on Kauai, so AIRMET Sierra that has been in place for mountain obscuration will likely be dropped soon. However with increasing areas of Oahu and Maui County experiencing MVFR conditions, expect an AIRMET Sierra to likely be posted for those areas shortly. Anticipate improvement in these areas after sunrise.

Marine

Surface high pressure far north of the state and a trough to our northeast will maintain fresh to locally strong northeast trade winds today. High-res guidance shows locally strong wind speeds in the typically windy waters around Maui County and the Big Island today, so those zones have been added to the Small Craft Advisory (SCA) through this afternoon. The incoming northwest swell will likely keep seas around 10 feet over the waters around Kauai and Oahu today, so the SCA has been extended for those zones through this afternoon. The high will gradually weaken over the next few days, but a ridge will remain north of the state during the first half of next week, maintaining moderate to locally fresh trades.
A new long-period northwest swell will continue to build this morning and peak around mid-day. Buoy readings from buoy 51101 showed peak deep water swell heights of around 9 feet or so and 16 seconds around midnight. Since this is a little higher than previously expected, have decided to issue a High Surf Advisory (HSA) for north and west facing shores of Niihau and Kauai, as well as north facing shores of Oahu, Molokai, and Maui through this afternoon. This swell will decline through Monday. The next northwest swell is scheduled to arrive Tuesday with similar size, so HSA conditions are possible again along many north and west- facing exposures late Tuesday into Wednesday. This swell will be reinforced by a more northerly swell late Wednesday into Thursday.
The trade winds over and upstream of the islands are generating choppy, rough seas along east-facing shores. A small south- southwest swell will continue to provide small surf today, before declining. Another small south swell is possible during the second half of this week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for north and west facing shores of Niihau and Kauai, and north facing shores of Oahu Molokai and Maui.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov