Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly cloudy. Breezy. Haze in the morning. Showers likely in the morning, then scattered showers in the afternoon. Highs 83 to 88 near the shore to around 73 above 3000 feet. East winds 15 to 20 mph. Chance of rain 60 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 69 to 74 near the shore to around 61 above 3000 feet. East winds 15 to 20 mph. Chance of rain 20 percent.

Thursday: Breezy. Sunny with isolated showers. Highs 83 to 88 near the shore to around 73 above 3000 feet. East winds 15 to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Haze in the morning. Showers likely in the morning, then scattered showers in the afternoon. Highs 80 to 87. East winds 15 to 20 mph. Chance of rain 60 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71. East winds around 20 mph. Chance of rain 50 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 87. East winds 20 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Haze in the morning. Showers likely in the morning, then scattered showers in the afternoon. Highs 71 to 79 in the valleys to around 64 above 4000 feet. East winds 15 to 25 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then showers after midnight. Lows 63 to 69 in the valleys to around 58 above 4000 feet. East winds 15 to 25 mph. Chance of rain 90 percent.

Thursday: Partly sunny. Windy. Showers likely in the morning, then scattered showers in the afternoon. Highs 71 to 79 in the valleys to around 63 above 4000 feet. East winds 15 to 30 mph. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Haze in the morning. Partly sunny with scattered showers. Highs 74 to 85. East winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 63 to 73. East winds 15 to 20 mph. Chance of rain 70 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 85. East winds 15 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Breezy. Haze in the morning. Showers likely in the morning, then scattered showers in the afternoon. Highs 72 to 83. East winds 15 to 20 mph. Chance of rain 60 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 75. East winds 15 to 20 mph. Chance of rain 50 percent.

Thursday: Breezy. Partly sunny with showers likely in the morning, then mostly sunny with scattered showers in the afternoon. Highs 71 to 82. East winds 15 to 25 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

High pressure building north of the islands will bring increasingly strong trade winds the next couple of days, with a trend toward fewer showers. Little change is expected over the weekend.

Discussion

A somewhat unstable and humid ESE flow remains in place over the Kauai end of the island chain this morning, due to an expansive kona low centered about 1000 miles to the NW. Associated convergent low- level flow is triggering a few heavy showers and isolated thunderstorms over waters S of Kauai and Oahu. Elsewhere, relatively small fast-moving showers are noted over windward portions of all islands, although coverage has been diminishing overnight. High clouds associated with the kona low are streaming over the islands from the SW, and are obstructing a view of lower cloud coverage using traditional IR imagery. However, a well-illuminated nighttime visible image indicated very little in the way of showers immediately upstream of the islands. Air quality sensors indicate that an area of vog that moved over the islands from Maui to Kauai on Tuesday continues to linger.
A trend toward strong E trade winds and increasingly stable conditions will begin today as the kona low moves W, and deep-layer high pressure builds N of the islands. Over the past 24-hours, surface pressures have increased by 4-6 mb statewide, indicating that this process is well underway. A few heavy showers may linger near Kauai in the short-term, but otherwise expect typical trade wind conditions, with showers focused mainly across windward slopes. The UH VMAP model also suggests that the vog will be diminishing today, and a building inversion between 7000 to 8000 ft should keep future emissions from Mauna Loa largely trapped aloft and carried to the W of the Big Island. Additionally, high clouds will be diminishing today, and should be completely gone by Thursday.
Trade winds will continue to strengthen tonight and remain gusty for the next several days, potentially continuing through part of the weekend. A robust surface high developing far N of the state will drive the stronger trade winds, and a ridge aloft will bring an increasingly strong subsidence inversion. This will lead to acceleration of winds over and downwind of terrain that may require a Wind Advisory, likely including the saddle and summit areas of the Big Island. Expect rainfall to favor windward slopes, though some showers will be blown over to leeward areas from Maui to Kauai at times. An upper low passing S of the state this weekend could increase shower chances on the Big Island, but models have been trending drier, especially for Saturday.

Aviation

A high pressure ridge will build to the north of the islands as a deep low pressure system northwest of the state continues to drift slowly westward. Strong and gusty winds are forecast and winds will shift from a southeast to east direction today. Expect periods of showers with brief MVFR/IFR conditions over the next 24 hours mainly over windward and mountain areas.
AIRMET SIERRA in effect for mountain obscuration over east portions of the Big Island and Maui, and north through east sections of Oahu and Kauai due to low clouds and showers.
AIRMET Tango in effect for tempo moderate turbulence below 080 over and immediately SW through NW of island mountains due to strong winds.

Marine

High pressure centered far northeast of the islands, along with a strong low approximately 1,000 miles northwest of Kauai, will maintain a tight enough pressure gradient across and upstream of the local waters to support several days of fresh to locally strong east trade winds. Mid to late week winds channeling through the Pailolo and Alenuihaha Channels, as well as south of Big Island, will occasionally reach gale force. Thus, a Gale Watch is in effect for these marine zones from early Thursday morning through Friday night. As the low drifts further west away from the state, thunderstorms forming along the low's leading stationary boundary may graze and impact the waters west of Kauai and Niihau, or west of 160W, through the day. High pressure will build in the wake of the low and keep the northeast-to-southwest pressure gradient tight across the area. A Small Craft Advisory is now in effect for all waters to account for both strong winds and/or high seas.
A moderate, medium period northwest (310-320 degrees) swell is peaking early this morning and will begin to fall through the day. Due to this slow fall, the High Surf Advisory (HSA) has been extended through this afternoon for the north and west-facing shores of Niihau, Kauai, Oahu and Molokai. A very small, medium period reinforcing northwest bump arriving Thursday will keep swell from completely falling off, thus holding waist to head high surf through early Saturday along many north-facing shores. Strengthening trades will significantly increase east-facing shore chop. Rough east surf will stick around into the weekend and may near 10 foot HSA levels Thursday night and Friday.

Fire weather

Models are showing drying in the low levels on Thursday into Friday, which could significantly lower afternoon relative humidity across leeward areas, and trade winds will be strong and gusty during this time. Many leeward areas have yet to experience significant rainfall early this wet season, and critical fire weather conditions may occur.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for North and West facing shores of Niihau Kauai Oahu and Molokai.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters, Oahu Leeward Waters, Maui County Leeward Waters.
Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay, Big Island Southeast Waters, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters.
Gale Watch from Thursday morning through late Friday night for Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov