West Kaua’i

Today: Mostly sunny with isolated showers. Highs 86 to 93 near the shore to around 79 above 3000 feet. North winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 73 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 86 to 92 near the shore to around 79 above 3000 feet. East winds up to 15 mph.

South Kaua’i

Today: Mostly sunny with isolated showers. Highs 84 to 92. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 83 to 91. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers. Highs 77 to 86 in the valleys to around 69 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 65 to 71 in the valleys to around 59 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 76 to 86 in the valleys to around 68 above 4000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 79 to 89. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 65 to 74. East winds up to 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 79 to 89. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 77 to 89. Northeast winds up to 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 78. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 76 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

High pressure ridging north of the Hawaiian Islands and a weak low propagating westward south of the islands will maintain stable weather conditions under moderate to locally breezy trades throughout the day. A shift in weather begins Tuesday, as a brief uptick in shower activity is expected as a batch of deeper moisture meanders into the vicinity of the state. For the latter end of the week through the weekend, expect periods of showers with increased cloud coverage associated with another batch of deep moisture.

Discussion

Broad area of high pressure and associated ridging remains quasi-stationary just north of the Hawaiian Islands as a weak low pressure system continues to propagate westward south of the state, producing a tight pressure gradient responsible for increased wind speeds. Stable conditions will maintain a relatively dry summer weather pattern with moderate to locally breezy trades through the day today, decreasing slightly through early Wednesday.
As the week progresses thereafter, trades increase slightly, as well as bring an uptick in shower activity and increasing cloud coverage as a batch of deeper moisture moves into the vicinity of the islands, primarily impacting windward and mauka areas, however, leeward areas may see some of the stronger trade wind showers. That said, these showers will dissipated as quickly as they arrive and overall moisture content will be limited.
Latest deterministic model guidance suggests unsettled weather conditions continue Thursday, persisting through much of the weekend. Guidance depicts a frontal system extending well north from the Gulf of Alaska and extending southward south of 40N. This front will perpetuate trades with deeper moisture ahead of the aforementioned high pressuring pinching off the tail end, pivoting this moisture toward the vicinity of the islands. The excess deeper moisture will coincide with the latter end of this week's progged temperature inversion levels, situated around the 7,000 foot elevation level, supportive of isolated to scattered showers throughout the day, and scattered to numerous showers overnight through the weekend. While the increase trade wind showers will higher coverage predominately across windward and mauka areas, it cannot be ruled out that leeward areas may see brief spillover.

Aviation

Moderate to locally breezy trade winds will continue through the forecast period. Limited clouds and showers will favor windward and mauka areas, with a slight uptick during the overnight hours. Conditions remain predominately VFR, with brief MVFR possible under passing showers.
No AIRMETS are in effect and none are anticipated through the forecast period.

Marine

Moderate to locally strong trades expected through this afternoon. As such a Small Craft Advisory (SCA) remains in effect for the windier channels and waters around Maui and the Big Island through 6PM tonight. A high to the north will weaken slightly on Tuesday allowing trades to ease. Winds should restrengthen by mid- week bringing back a SCA.
The recent small, medium period north swell will slowly decline today. Another medium period north swell is expected to arrive Thursday and may cause a slight bump in surf along north- facing shores.
A small, medium- to long-period south swell will keep surf along south-facing shores near the September averages gradually declining tonight through mid-week. A couple of very small reinforcements are expected throughout the week, though surf will remain small. A slightly larger, long-period swell is forecast to arrive in the islands Friday night, boosting south shore surf next weekend.
East facing shores will see typical trade wind generated energy throughout the forecast period.

Fire weather

Low humidity levels persist with sustained winds just under critical fire weather thresholds for a few hours this afternoon. Expect decreasing fire weather concerns beginning tomorrow onward through the forecast period as minimum humidity levels increase.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.