Photo Credit: Jason Weingardt

West Kaua’i

Tonight: Mostly clear. Lows around 63 near the shore to around 52 above 3000 feet. Light winds.

Wednesday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 71 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 65 near the shore to around 54 above 3000 feet. Light winds. Chance of rain 30 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 59 to 64. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 82. Light winds. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 61 to 66. Light winds. Chance of rain 30 percent.

Kaua’i Mountains

Tonight: Partly cloudy. Lows 52 to 57 in the valleys to around 46 above 4000 feet. Light winds becoming west up to 10 mph after midnight.

Wednesday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 70 to 78 in the valleys to around 65 above 4000 feet. West winds up to 10 mph shifting to the northeast around 10 mph in the afternoon. Chance of rain 30 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 54 to 59 in the valleys to around 48 above 4000 feet. Southwest winds around 10 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Partly cloudy. Lows 55 to 64. Light winds.

Wednesday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 82. Light winds. Chance of rain 30 percent.

Wednesday Night: Partly cloudy with scattered showers. Lows 57 to 66. Light winds. Chance of rain 30 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 53 to 65. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 75 to 82. Northeast winds around 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 55 to 67. Light winds. Chance of rain 30 percent.

Detailed Forecast

Synopsis

A weak ridge north of the islands will continue to produce light southeasterly background winds across the region through Thursday. Sea breezes will develop over each island building clouds and producing a few showers over island interior sections in the afternoon to early evening hours. The weather pattern trends wetter from Thursday onward as an unstable upper level trough moves into the region. An approaching cold front will produce southerly winds across the western half of the state this weekend, with the potential for heavy rain and thunderstorms near Kauai and Oahu. Moderate to breezy trade wind weather returns by early next week.

Discussion

A weakened surface ridge just north of the islands will keep light background southeasterly wind flow blowing across the Hawaii region through Thursday. The upper level ridge stacks back in the warm air to a position directly over the islands. Stable air under this ridge will keep temperature inversion heights in the 5,000 to 7,000 foot range and will continue to produce stable conditions across the island chain through Wednesday.
The large scale weather pattern changes starting on Thursday with increasing shower trends as the warm and stable upper level ridge is replaced by a cold unstable upper trough. Trade wind temperature inversion heights rise to around 10,000 feet allowing deeper cumulus cloud development and the possibility for even a few thunderstorms near Kauai on Thursday night. Light winds with sea breezes and scattered to numerous showers will likely continue through Friday.
A cold front begins to approach the islands from the northwest from late Friday through Saturday. Winds will veer towards southerly directions for the western islands of Kauai and Oahu during this time period with lighter southeasterly winds expected to continue over all islands in Maui and Hawaii Counties. Southerly winds ahead of the frontal trough will pull up unstable tropical moisture and enhance showers especially along southern slopes of Kauai and Oahu from Friday night through Saturday night. Numerous showers are forecast along the cold frontal band as it moves into Kauai around midnight Sunday morning, the front then stalls near the island of Kauai by Sunday morning with shower activity picking up over Oahu. This weather pattern favors periods of heavy rain and thunderstorm development over the western islands this weekend. However, it remains too early at this point to pin down island by island impacts. The eastern Hawaiian Islands will see moderate trade winds build back in on Sunday, with more isolated to scattered showers focused mainly over windward slopes. Extended range guidance early next week hints at a second cold front moving into to Hawaii region, possibly producing another round of wet weather for the islands.
There remains some disagreement on the timing and location of the approaching frontal band this weekend. Current forecast guidance is stalling out the frontal shower band just northwest of Kauai. However, we blended forecast solutions from both the current and previous American (GFS) model and the European (ECMWF) models for the Saturday to Sunday forecast to smooth out errors from any one model solution. Stay tuned for updates for this weekends wet weather as island by island forecast impacts will evolve over time.

Aviation

A weak surface ridge just north of the area is maintaining relatively light background east-southeast winds in the vicinity of the state. The atmosphere also remains dry and stable across the region. Therefore, low clouds and showers remain limited, especially near the smaller islands. The east-southeast flow will likely deliver scattered low clouds and a few showers into east through southeast sections of the Big Island this morning. This may produce brief periods of MVFR ceilings along portions of the windward Big Island, but VFR conditions are expected to prevail across most of the state today.
Expect local sea breeze circulations to become established over each of the islands this afternoon. This may produce some low clouds and a slight chance of showers mainly over leeward and interior sections during the afternoon. This will be followed by local nighttime land breezes this evening. These downslope winds will tend to clear out most of the residual cloud cover over the interior and leeward sections of the islands soon after sunset.
No AIRMETs are currently in effect, and none are anticipated through today.

Marine

Weak high pressure will hold in place northeast of the islands during the next several days, while a front gradually dissipates to the northwest. As a result, winds will change little across the marine area through Thursday, with light to moderate east- southeast winds holding in place near Maui and the Big Island, and light and variable winds prevailing elsewhere. Moderate to fresh southeast to south winds are forecast to develop ahead of an approaching front Friday and Saturday, with light to moderate trades potentially filling back in late Sunday into early next week as the front dissipates and a new area of high pressure builds north of the island chain. Winds and seas are forecast to remain below advisory thresholds through Friday, with advisory level winds potentially developing across portions of the marine area Friday night and Saturday.
The current large northwest swell has dropped just below advisory levels early this morning, and as a result the High Surf Advisory has been cancelled. Surf along north and west facing shores is not expected to drop much today however, with a slight decline then expected tonight. A couple new reinforcing northwest swells are expected Wednesday and Thursday, although surf heights should remain below advisory levels. A new large northwest swell could bring another round of advisory level surf to north and west facing shores on Friday, with a dip below advisory levels forecast for Saturday, followed by a potential extra large event Sunday through Monday with surf heights well above warning thresholds.
The current small south swell will continue to decline today, with only background south swell energy expected Wednesday through the weekend. A new small long-period south swell could give south shore surf a minor boost early next week. East shore surf will remain small and well below normal through the upcoming weekend due to the lack of trade winds over and upstream of the islands. Returning trades could give surf a boost along east facing shores early next week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov