Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny. Scattered showers in the afternoon. Highs around 82 near the shore to around 70 above 3000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly clear. Lows 65 to 70 near the shore to around 58 above 3000 feet. Light winds.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs around 82 near the shore to around 71 above 3000 feet. West winds around 10 mph shifting to the north in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 79 to 84. Northeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly clear. Lows around 67. North winds around 10 mph.

Saturday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 79 to 85. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Sunny with isolated showers in the morning, then cloudy with showers in the afternoon. Highs 70 to 77 in the valleys to around 63 above 4000 feet. Light winds. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 65 in the valleys to around 55 above 4000 feet. Light winds. Chance of rain 50 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then showers in the afternoon. Highs 71 to 77 in the valleys to around 63 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

North Kaua’i

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 82. Northeast winds around 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with isolated showers. Lows 61 to 69. Light winds. Chance of rain 20 percent.

Saturday: Partly sunny. Isolated showers in the morning, then showers likely in the afternoon. Highs 73 to 82. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 81. Northeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 61 to 71. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 72 to 82. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Emerging sea breezes will bring interior clouds and showers this afternoon, especially to Kauai and Oahu. Moderate trades will gradually build from west to east across the state during the period spanning this evening to Sunday evening.

Discussion

Clouds trapped beneath the inversion have very slowly thinned and begun to dissipate this morning at least partly in response to modest dry advection from the northwest at and above 800mb. This increases confidence that daytime heating will get underway largely uninhibited and should have no issue touching off interior clouds and showers late this morning into the afternoon, particularly over Kauai and Oahu where greater low-level moisture quality resides. Until then, dry conditions will prevail for nearly all areas with the exception of a stray shower or two developing over immediate coastal locales. Ridging building toward the western end of the state is modeled to bring a stronger push of trade winds to Kauai this evening resulting in a transition from interior convection today to shallow showers along windward slopes overnight. Likewise, the slow return of trades from west to east leads to the probability for a land and sea breeze pattern increasing with eastward extent. As it stands, moderate trades will arrive over the western end of the state this evening into tonight and Oahu late tonight or on Saturday morning. Trades then gradually build eastward encompassing the remainder of the state no later than Sunday evening. It follows that the probability of renewed land and sea breeze development will increase with eastward extent tonight through Sunday while a typical moderate trade wind pattern prevails elsewhere. By Sunday evening, a moderate to perhaps locally breezy trade wind pattern is forecast to prevail at all locations. Potentially, the gradient remains light enough during this time to allow for some enhanced convergence and afternoon clouds over the most sheltered areas. The progressive mid-latitude pattern is modeled to bring another round of pressure falls to the Central Pacific next week causing trades to weaken once more.

Aviation

Light northeast to east winds will give way to a localized land and sea breeze regime as a front approaches from the north. Broad upper trough combined with the approaching boundary and light winds will support afternoon showers developing over interior and mauka sections where sea breezes form today. North- northeast winds will gradually begin to pick up over the western end of the state as the ridge noses eastward in the wake of the front moving in. This could translate to increasing shower coverage for north facing slopes, especially over Kauai and potentially Oahu later today through tonight. AIRMET Sierra for MVFR CIGS/VSBYs in and around showers will remain possible through the morning hours over windward Oahu.

Marine

High pressure cells are centered well NE and NW of the islands this morning, with a weakness in the ridge just N of the islands due to a distant front approaching from the N. Latest analysis also shows a low-level trough over the area, currently analyzed between Kauai and Oahu. Light NE winds exist over Kauai waters, with light to locally moderate E to SE winds elsewhere, although overnight ASCAT pass indicated E winds near 20 kt near the Big Island. Little overall change to this pattern is expected today as the front moves closer to the islands, and the trough remains nearly stationary.
The high to the distant NW will move slowly E the next couple of days, and the nearby trough will dissipate tonight. Moderate to locally strong NE trade winds are expected to spread from Kauai waters to the remaining waters from tonight through Sunday in response, with winds likely reaching Small Craft Advisory (SCA) speeds in the windier zones around Maui and the Big Island by Sunday. Some weakening of the trade flow is possible early next week as the high weakens NW of the islands. The high will also act to push the weak frontal boundary over the area, bringing increased showers, mainly over windward waters.
Several pulses of medium-period NNW (340 degrees) swell are expected to arrive through the weekend, with the swell gradually shifting to the NNE early next week. The strongest of the pulses (potentially up to 10 feet of swell) will lead to High Surf along most N facing shores this weekend, with SCA-level seas in many seas. The first pulse arriving now will support elevated surf today, with surf remaining well below High Surf Advisory (HSA) heights. The next pulse will be unseasonably large, building tonight and Saturday, likely peaking Saturday night and Sunday. The low responsible for this swell will persist far NE of the islands, supporting elevated medium-period NNE swell into the middle of next week.
Relatively small but persistent medium to long-period S (170-180 deg) and SSE (140-160 deg) swells will continue for at least the next couple of days, with some long-period energy from the SW also possible next week. This will keep surf near seasonal averages along all S facing shores for the foreseeable future. Surf along E facing shores will remain small as upstream trade wind flow remains interrupted, but there will likely be some wrap from the NNE swell next week to bring a modest increase in surf heights.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov