Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to around 70 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 66 to 71 near the shore to around 57 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Sunday: Mostly sunny in the morning then becoming partly sunny. 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.

South Kaua’i

Today: Partly sunny. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 79. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 66 to 71. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Sunday: Partly sunny. 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.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then showers in the afternoon. Highs 68 to 74 in the valleys to around 63 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 showers. Lows around 61 in the valleys to around 53 above 4000 feet. Northeast winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 90 percent.

Sunday: 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.

North Kaua’i

Today: Partly sunny. Breezy. Scattered showers in the morning, then showers in the afternoon. Highs 70 to 79. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy. Breezy. Showers in the evening, then numerous showers after midnight. Lows 61 to 69. East winds 10 to 20 mph. Chance of rain 80 percent.

Sunday: Partly sunny with numerous showers. Highs 71 to 80. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then showers in the afternoon. Highs 70 to 80. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy. Breezy. Showers in the evening, then numerous showers after midnight. Lows 59 to 71. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

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

Detailed Forecast

Synopsis

Moderate to breezy trades will continue through the weekend, before dropping to moderate levels Monday and Tuesday, then easing into the light to moderate range by the middle of next week. Some showery weather will affect windward sections of the smaller islands this weekend, with showers reaching leeward locales more regularly as well. Bands of clouds and showers will continue to move through at times during the upcoming work week, with the showers favoring windward slopes and coasts.

Discussion

Currently at the surface, a broad trough of low pressure is located several hundred miles east and northeast of the state, while a 1028 mb high is centered around 1150 miles north of Honolulu. The resulting gradient is producing breezy northeast trade winds in unsheltered areas early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions, with radar imagery showing scattered showers moving into windward areas and some of these decaying showers reaching leeward sections of the smaller islands. Main short term focus revolves around the strength of the trades and rain chances during the next couple days.
The trough of low pressure east of the state will remain nearly stationary and dampen out during the next few days. Meanwhile, the high and associated ridge north of the state, will weaken and shift southward and closer to the island chain. Moderate to breezy northeast trade winds will generally prevail through early next week, with only minor fluctuations in strength. A decaying front shifting southward toward the state will weaken the ridging north of the islands late Tuesday through Friday, easing the trade winds and shifting them around to a more easterly direction.
The winds have dropped below advisory thresholds over Maui County and the Big Island, so the Wind Advisory has been cancelled for these areas.
As for the remaining weather details, remnant moisture associated with a dissipated low caught up in the northeast trade flow will be enhanced by a shortwave trough moving southeast through the state today through Sunday morning. This is expected to bring some showery weather particularly to windward sections of the smaller islands, with showers reaching leeward areas as well. Shower coverage should decrease Sunday afternoon as mid and upper level ridging builds over the islands. Yet another approaching shortwave trough is then expected to enhance a band of showers moving slowly southward through the islands Sunday night through Tuesday, but there remains timing and progression differences between the models. A drier trade wind pattern could develop during the middle to latter part of next week, particularly over the western end of the state, but details this far out remain uncertain at this time.

Aviation

The tight pressure gradient between a surface high pressure system far north of the islands and surface trough east-northeast of the Big Island will continue to produce locally strong northeasterly winds today. An upper-level short-wave trough is also moving across the state, which is making the atmosphere somewhat less stable. As a result, there appears to be some enhancement of the low clouds and showers, which are being transported down from the northeast. Expect brief periods of MVFR CIG/VIS due to these low clouds and showers over many north through east facing slopes and coasts today. In addition, a few brief showers may also make it over to the leeward sections of some of the smaller islands. Otherwise, VFR conditions are expected to prevail over most of the state today.
AIRMET Tango will likely remain in effect for TEMPO moderate low- level turbulence over and downwind of the higher terrain on all islands into Sunday. In addition, an upper-level jet stream extending east-northeast from near the eastern end of the island chain may be producing turbulence aloft. AIRMET Tango for moderate upper-level turbulence remains in effect near Maui and the Big Island. The expectation is that the potential for turbulence aloft will gradually diminish, and shift east of the state later today. Finally, we do not anticipate the need for AIRMET Sierra for mountain obscuration today, since most of the lower ceilings are expected to be near, or above 3 thousand feet.

Marine

Surface high pressure north of the state will be the main driver to continued fresh northeast trade winds through the day. The strongest winds will be where the pressure gradient is the tightest and this will be over more central and western waters. The Small Craft Advisory (SCA) will remain in effect for all nearshore waters surrounding the Hawaiian Islands through the day. These winds have lifted nearshore seas to around 8 feet. As a moderate size north northeast swell fills in through the morning and plateaus this afternoon, more western seas should near the SCA threshold of 10 feet tonight into early Sunday morning. Although winds will drop below SCA thresholds tonight, the SCA has been extended tonight over the local coastal waters from the Oahu windward waters westward to account for higher seas as an early week northwest swell begins to fill in. Surface high pressure northwest of the state will nudge its way in under a low far north of the region. As it does, it will slightly weaken this northerly pressure gradient and maintain moderate trades through the middle of next week.
A moderate size, short period north northeast swell (20-30 degrees) has been filling in this morning but has been a little underwhelming with relation to recent model runs. This swell will continue to steadily rise and peak out today. A longer period, slightly larger size northwest swell (320-330 degrees) will begin to fill in underneath this north northeast swell today and peak later tonight into Sunday. This swell may push surf up to near High Surf Advisory (HSA) thresholds on faces along the smaller island north-facing shores Sunday. The next potentially larger northwest swell is scheduled to arrive Tuesday. This swell will likely lift surf to HSA levels along many north and west-facing exposures late Tuesday into Wednesday. These recently fresh trade winds upstream of the islands are generating choppy, rough seas along east-facing shores. A small south southwest bump in swell will begin arriving along south shores this morning and will produce a minor uptick in south-facing shore surf this weekend. Another small south swell is possible during the second half of next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.
Small Craft Advisory until 6 PM HST this evening for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov