Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny. Highs around 80 near the shore to around 69 above 3000 feet. North winds up to 10 mph.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Lows around 65 near the shore to around 55 above 3000 feet. Northeast winds up to 10 mph.

Wednesday: Partly sunny. Highs around 82 near the shore to around 69 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Today: Mostly cloudy. Isolated showers in the morning. Highs around 78. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows around 65. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning. Highs 77 to 82. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 68 to 73 in the valleys to around 61 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 56 to 61 in the valleys to around 51 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 69 to 75 in the valleys to around 62 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy with isolated showers. Highs 71 to 79. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows 58 to 67. East winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers. Highs 73 to 81. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

East Kaua’i

Today: Mostly cloudy with isolated showers. Highs 69 to 79. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows 57 to 68. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly cloudy with isolated showers. Highs 71 to 80. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A high pressure system will slowly build north of the islands over the next few days producing moderate to locally breezy trade winds through Thursday. A weakening cold front caught between the building high and the Hawaiian Islands will delay breezy trade winds until Friday. These stronger trade winds will last through Sunday. Decreasing wind speeds to more moderate levels will return early next week as the high center drifts eastward away from the island chain. Brief passing shower activity will favor windward and mountain areas with increasing shower trends from Thursday onward.

Discussion

The infra-red satellite imagery this morning shows a weakening cold front roughly 400 miles northwest of Kauai. This front will pass north of the island chain later this week and briefly block stronger trade winds from a building high pressure system that will also pass by north of the islands over the next few days. High cirrus clouds associated with a subtropical jet stream are filling in over the state today and will continue to produce extensive high cloud cover across all islands through Wednesday. Fairly stable pillow shaped stratocumulus clouds are moving into the island on the east-northeasterly trade winds this morning. These stable clouds are riding in under a stable subsidence temperature inversion height of around 5,000 feet elevation, keeping showers to a minimum through Wednesday.
By Wednesday night into Friday, weather conditions begin to shift a bit as forecast guidance shows an upper level trough moving in from the northwest and deepening over the islands. Colder air and upper level divergence associated with this trough pattern will decrease stability a bit, raising the temperature inversion heights, producing deeper more unstable clouds, and increasing shower trends. These showers will tend to favor the overnight to early morning hours with the highest shower coverage expected over the typical windward and mountain areas. Trade winds also increase in strength to breezy levels from Friday through Sunday.
The weather forecast for this weekend is complicated by a small upper level low drifting into the Hawaii region. This system may enhance shower activity over some islands as model guidance tends to be less certain on these smaller scale features this far out in time. For now we are forecasting a normal trade wind shower pattern with scattered to numerous showers at night favoring windward areas. These showers could intensify for some islands this weekend if this low tracks closer to the state than our recent forecast model and model blends suggest. Stay tuned.
.AVIATION… Moderate easterly trades will persist, with clouds and light showers favoring windward and mauka areas overnight through the morning hours. VFR conditions will persist, with only a slight chance of MVFR CIGs/VSBYs for brief periods in showers.

Marine

Trades have generally eased back to more moderate to locally fresh magnitudes as a result of high pressure settling in north of the coastal waters. There will be a slight pick up in trades through the notoriously windier eastern island channels and bays around Maui County and south of Big Island this afternoon. This has prompted a Small Craft Advisory for these waters through Wednesday afternoon. The next high developing farther north of the region Wednesday will build south Thursday and Friday. This will tighten the regional pressure gradient across the local waters and strengthen trades back to fresh to locally strong levels going into the weekend.
The early week northwest (310-320 degree) swell is continuing to fall through the day. It will be followed by a slightly larger size northwest (310-330 degree) swell building in later tonight. This swell's forerunners are now passing around the far northwest offshore buoys during the pre-dawn morning hours. This times the swell to fill in through the afternoon hours and peak along Kauai-to-Maui's better exposed north and west-facing coasts from late tonight through Wednesday. This high end moderate size, long period swell will likely produce High Surf Advisory (HSA) level north and west-facing shore surf tonight and Wednesday. North and west shore surf will fall below HSA heights Thursday. The next moderate size, medium to long period northwest (310 degree) swell is expected to arrive this weekend. The weak pulse of early season south southwest (200 degree) swell will fade out through the day. This inconsistent swell will keep south-facing shore surf slightly elevated through tonight with a gradual decline in surf as the swell fades Wednesday. East shore surf will remain small through Wednesday. There will be a slight pick up in east chop late this week in response to strengthened trades.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov