Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny. Breezy. Scattered showers in the afternoon. Highs around 83 near the shore to around 73 above 3000 feet. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 71 near the shore to around 57 above 3000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 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. East winds 10 to 15 mph. Chance of rain 40 percent.

South Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs around 81. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 70. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 81. East winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then occasional showers in the afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 60 in the valleys to around 52 above 4000 feet. East winds 10 to 25 mph. Chance of rain 60 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. East winds 15 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 75 to 82. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 75 to 82. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 80. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 58 to 71. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 74 to 80. East winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate trade winds will persist this morning, followed by an extended period of moderate to breezy trade winds from later today and tonight through mid-week. A weak disturbance aloft moving across the area will likely keep the windward sides of some of the islands rather wet through this evening. In addition, brief heavy downpours and a thunderstorm or two may develop over upslope sections of the Big Island this afternoon. Expect a rather typical trade wind weather pattern from Monday into mid-week, followed by a drying trend toward the end of the new work week.

Discussion

A 1032 mb surface high is near 38N 173W, or more than 1300 miles northwest of Lihue. This high, which is propagating toward the southeast at about 10 mph, is pushing a weakening frontal boundary down from the north toward the region. The cold front is currently located slightly more than 500 miles north of Honolulu, and it is moving toward the south-southeast at about 10 mph. Therefore, the pressure gradient remains relaxed across the main Hawaiian Islands, so that light to moderate trade winds prevail across most of the state early this morning.
A weak mid-level low, which appears to be near, or just south of the smaller islands, is drifting slowly eastward. The close proximity of the low aloft has caused some weak instability to develop over the central and western portions of the island chain overnight. Radar reflectivities indicate scattered trade showers are moving into the windward sides of most islands, especially from Maui to Oahu.
The forecast guidance continues to indicate the light to moderate trade winds will persist through this morning due to the frontal boundary pushing down closer to the region. The weak mid-level low will move slowly east across the area through this morning, but it may open up into a mid-level trough near the Big Island later today or tonight. The flow aloft around this feature may carry some thin high clouds across parts of the state through this evening. By this afternoon, the broad surface high pressure system that is currently far northwest of the area will continue to move down closer to the region. At the same time, the front will likely begin to weaken into a remnant boundary between 200 and 300 miles north of the state. This is forecast to allow the pressure gradient to tighten across the area, so expect moderate to locally breezy trade winds to become reestablished across most of the island chain from later today and tonight through early Monday. The close proximity of the weak mid-level low / trough to the Big Island may destabilize the atmosphere there later today. This combined with ample daytime heating may allow scattered showers with brief heavy downpours to develop over the upslope sections of the Big Island. In addition, a thunderstorm or two is possible on parts of the Big Island this afternoon. Elsewhere, expect relatively wet trade wind weather conditions to persist along many windward sections of the islands through tonight.
From Monday through the middle of next week, the broad surface high pressure system will move to a position far north of the region. This will likely maintain the breezy trade wind weather pattern at least through mid-week. The mid-level trough may linger near, or just east of the Big Island from Monday into mid- week, but the trade wind inversion is expected to gradually strengthen. Therefore, low clouds and trade showers will move over windward and mauka sections of the state. The gusty trades may also allow a few brief showers to reach leeward sections of some of the smaller islands, especially during the late night and early morning hours. In addition, expect clouds and showers to develop over the upslope sections of the leeward Big Island each afternoon, followed by gradual clearing late at night.
There are still some uncertainties in the weather pattern toward the end of the new work week. It does appear the ridging aloft will cause increasing stability over the area later in the week, so there may be a drying trend heading into Thursday and Friday. In addition, the latest forecast model trends continue to indicate the possibility of a weak surface trough forming to the east of the Big Island Friday. Another cold front may also push down to the north of the area, which may cause the subtropical ridge to weaken again heading into next weekend. If so, there may be a slight weakening of the trade winds later this week.

Aviation

A high pressure ridge building in far north of the state will boost light to moderate trade winds this morning into the moderate to locally breezy range later this afternoon. A weak upper level trough and embedded low near the islands will keep brief periods of showers and MVFR conditions in the forecast mainly along windward mountain slopes, favoring the overnight to early morning hours. Most leeward areas will remain in VFR conditions with the exception of the leeward Big Island, where converging sea breezes may produce periods of MVFR conditions, showers and possible thunderstorms this afternoon.
AIRMET Tango will return this afternoon as strengthening trade winds will produce periods of low level turbulence over and southwest through northwest of mountain ranges. The upper level turbulence will likely fade this morning as the upper level trough weakens.
Light icing will also remain in the forecast near Kauai through the afternoon hours.

Marine

Both ASCAT passes overnight missed the islands. Based on model guidance, have issued a Small Craft Advisory (SCA) for the typical windier waters near Maui County and the Big Island starting at noon today. Initially the SCA is out through Monday night, but in all likelihood will be extended into the middle of the week and expanded to include additional areas.
Building high pressure north of the islands is helping to drive the strengthening trade winds that will be with us into the middle of the week. The trade winds are expected to peak Tuesday into Wednesday with winds approaching gale-force in the windier waters near Maui County and the Big Island. Trade winds should gradually weaken during the second half of the new week.
Surf will remain rather small along all shores today. A moderate, medium period north (350 degree) swell should begin to fill in Monday afternoon, peaking Tuesday at moderate heights, and then steadily drop through Wednesday. A smaller long-period northwest (320 degree) swell is possible Friday through next weekend. Surf along east facing shores should see a steady increase of rough and choppy surf Monday through the middle of the week as trade winds strengthen. Surf could approach High Surf Advisory thresholds during the middle of the week. South surf will remain small for the foreseeable future with mainly background swells and trade wind wrap. Some small long period south swells will be possible towards the later half of the week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov