Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 88 near the shore to around 77 above 3000 feet. East winds around 10 mph shifting to the south in the afternoon. Chance of rain 30 percent.

Tonight: Mostly clear. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds around 10 mph.

Wednesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 89 near the shore to around 78 above 3000 feet. Northeast winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Sunny. Highs around 89. East winds around 10 mph.

Tonight: Mostly clear. Isolated showers in the evening. Lows 72 to 77. North winds around 10 mph. Chance of rain 20 percent.

Wednesday: Sunny. Highs around 89. North winds 10 to 15 mph shifting to the east in the afternoon.

Kaua’i Mountains

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 77 to 85 in the valleys to around 69 above 4000 feet. East winds around 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 66 to 72 in the valleys to around 61 above 4000 feet. East winds around 10 mph shifting to the southwest after midnight. Chance of rain 20 percent.

Wednesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 77 to 87 in the valleys to around 69 above 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

North Kaua’i

Today: Sunny in the morning then becoming partly sunny. Isolated showers. Highs 79 to 88. Southeast winds around 10 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 66 to 74. Southeast winds around 10 mph shifting to the south after midnight. Chance of rain 20 percent.

Wednesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 79 to 89. Southeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 20 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 79 to 90. North winds around 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 66 to 79. Northeast winds around 10 mph shifting to the west after midnight. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 78 to 90. Northwest winds around 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Light trade winds will prevail the next several days, strengthening somewhat over the weekend. Mostly dry weather is expected through the period for most areas. The light winds may deliver an isolated overnight shower to windward areas, while afternoon sea breezes will bring clouds and a few showers to leeward areas. Increased moisture may move over the Big Island Wednesday and Thursday, potentially fueling increased shower coverage there. High clouds of varying thickness will periodically move over the islands the next couple of days.

Discussion

Morning satellite images show few to scattered relatively thin high clouds streaming northeastward over the islands from Oahu to the Big Island, somewhat obscuring low cloud coverage in infrared imagery. A pair of nighttime visible (VIIRS) images did “shed some light” on this, indicating that few to scattered low clouds prevailed, with scattered to broken low clouds over leeward Big Island. Radar shows just a few showers moving WNW over windward waters, although light rain loitered near the Kona airport for a good portion of the night. Land-based surface observations indicate offshore-flowing land breezes in most areas, except for light E winds at the most exposed windward locations.
The typical trade wind flow is diminished and veered toward the ESE due to a surface low and surface troughs passing between the islands and the trade-wind-supporting ridge to the N. Morning soundings showed PWAT slightly below average (~1.2″), with a subsidence inversion near 5000' at PHTO, and a lack of an inversion in the PHLI sounding. The lack of an inversion in the Kauai sounding is likely associated with a mid- to upper-level low and trough NW of Kauai, with the subtropical jet (STJ) on its SE side providing the high clouds. Elsewhere, an area of deep moisture is pooled about 400 to 700 miles S of the Big Island.
The low to the distant NW will move further W through tomorrow, but lingering troughing to the NE of the islands will continue to keep the ridge in a weakened state for several days. Winds will back to more typical easterly direction on Wednesday, and speeds may increase just a tad, but they will likely remain light enough for land and sea breezes to strongly modulate island weather through Friday.
While the trades may deliver an isolated shower or two, mainly during nights and mornings, clouds and limited showers will focus over leeward areas during afternoon hours as sea breezes develop in response to daytime heating. Limited moisture will result in just a few showers in most areas, but guidance indicates that the deep moisture S of the islands will move N and clip the Big Island Wednesday into Thursday. Dynamic lift provided by the STJ may lead to increased coverage of clouds and showers there, while also bringing the potential for an afternoon thunderstorm over the slopes on Wednesday and Thursday. Thereafter, mostly dry weather is expected statewide through the weekend as a strong mid-level ridge builds over the area from the E. Meanwhile, the low aloft to the NW will continue to bring periodic bouts of high clouds this week, especially over the SE end of the island chain, although there is some uncertainty as to how thick they become.

Aviation

Light east-southeast low-level background flow will continue through the 24 h forecast period, allowing localized overnight/early morning land breezes and daytime sea breezes to develop. Clouds and light showers will favor windward coasts through the morning hours, then interior and leeward locations during the afternoon/early evening hours where sea breezes form. VFR conditions will prevail, with only brief periods of MVFR CIGs/VSBYs in showers.
AIRMET TANGO for moderate turbulence between FL300 and FL450 will likely continue today.

Marine

Two surface troughs just north of the Hawaiian Islands will continue to weaken the high pressure ridge farther north of the state through much of this week. Gentle to moderate trade winds will allow local scale land and sea breezes to develop along near shore coastal waters each day, especially over leeward areas. Trade winds are expected to strengthen later this weekend.
A long period south swell will gradually build over the next 12 hours with south shore surf heights approaching High Surf Advisory thresholds today through Wednesday. Buoys are reporting this building south swell around 1 foot over GFS wave model guidance. South swell heights are forecast to reach the 3 to 4 foot and 17 to 18 second period range today through Wednesday morning with the swell period starting to decline by Wednesday afternoon. This south swell energy will continue to decline from through Friday.
No other significant swells are expected this week. A tiny northwest swell will fade today, and with trade winds trending lower, east shore surf will be below seasonal average heights through much of the week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov