Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 83 near the shore to around 70 above 3000 feet. Northeast winds 10 to 15 mph shifting to the northwest in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 67 near the shore to around 57 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 84 near the shore to around 71 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny with isolated showers. Highs 78 to 84. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 67. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 78 to 84. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 70 to 77 in the valleys to around 62 above 4000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 60 to 65 in the valleys to around 55 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Monday: Breezy. Mostly cloudy with numerous showers. Highs 71 to 77 in the valleys to around 63 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 73 to 83. Southeast winds 10 to 15 mph shifting to the east in the afternoon. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 69. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 83. East winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 70 to 82. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 70. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy with numerous showers. Highs 70 to 82. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate trade winds will continue through today, before gradually strengthening through the first half of the week. Trades will likely become strong by the middle of the week, then remain strong into next weekend. Passing clouds and showers will favor windward areas, with shower coverage increasing Monday, and potentially persisting through much of the week.

Discussion

A 1031 mb surface high far NE of the islands will support a moderate trade wind flow through today. Radar shows scattered showers moving along windward areas with a few showers spilling over to leeward areas of the small islands. Clouds and showers are expected to become more sporadic this afternoon as the atmosphere dries out slightly. Winds will ease slightly today as a front approaches from the northwest then stalls. Seabreezes could develop this afternoon, resulting in an increase in clouds and possible isolated showers along shelter leeward and interior locations.
The approaching front will stall and weaken to a trough several hundred miles NW of the islands Monday and Tuesday, but trade winds will gradually strengthen as the high to the NW tightens the local gradient. The island atmosphere will remain relatively stable, but a showery cloud band seen on satellite (a frontal remnant extending through 23N154W to 21N150W) will arrive Monday. This boundary will bring increased showers, especially windward, through at least Tuesday night.
By late Tuesday into Wednesday, a longwave trough aloft will develop W of the islands, with several impulses aloft diving into the trough. This is expected to lead to the development of a mid- level cutoff low to the NW, thereby initiating surface cyclogenesis along the stalled trough. The low is expected to develop about 500 miles NW of Kauai on Wednesday, then move W through Friday as the high passes N and NE of the islands.
Strong E to ESE winds will develop over the islands Wednesday, easing ever so slightly Thursday and Friday. The longwave trough and cutoff low may develop close enough to the islands to the destabilize the atmosphere and combine with the lingering moisture to bring some locally heavy showers, mainly to Kauai around Wednesday. Otherwise, it appears that a wet trade wind weather pattern will prevail as the mid-levels remain cool through the week.

Aviation

A high pressure system currently far northeast of the state will continue to slowly weaken and drift eastward away from the island chain as a cold front approaches the Hawaii region from the northwest. Trade winds will decrease slightly by this afternoon. Expect periods of showers mainly over windward and mountain areas as two cloud bands move over the islands through Monday. These additional clouds and showers will produce brief periods of MVFR conditions over windward airfields favoring the overnight to early morning hours. Mostly VFR conditions will prevail.
AIRMET Sierra for mountain obscuration remains in effect for north through east slopes of Kauai, Oahu, Molokai, Maui and the Big Island. This AIRMET will likely last through the early morning hours.

Marine

A cold front that is currently far northwest of the main Hawaiian Islands will push eastward over the next several days, displacing surface high pressure to the northeast. The short term trend will be toward weakening winds today. Trade winds will be just below the Small Craft Advisory (SCA) criteria today but may trend back up tonight for the typical windy waters around Maui County and the Big Island.
During the first half of the week, a surface trough is expected to develop between the coastal waters and the anomalously strong high pressure building in north of the islands. Typically with the high pressure we would anticipate strong to gale force winds, the surface trough will likely prevent trade winds from reaching their full potential across the coastal waters initially. Winds will build to fresh to strong speeds over Kauai and Oahu waters, and strong to locally near gale force over Maui County and the Big Island on Tuesday. By mid to late week, strong trades will become more widespread as a surface low forms northwest of the islands.
A small, medium period northwest swell is slowly filling in today for north and west facing shores keeping small surf. A series of small medium period reinforcements from the northwest will keep surf from going flat over north and west facing shores through the first half of the week. An upward trend is possible beginning Tuesday as a moderate sized, short- to medium- period north swell arrives from the low that is forecast to develop north-northwest of the islands.
Surf along east facing shores will ease a bit on today as trade winds ease. With the onset of strong trade winds on Tuesday, rough choppy surf is expected as a SCA is likely for seas 10 feet or greater Tuesday through the end of the week. Surf along south facing shores will remain small for the next several days. By the weekend, a small medium- to long- period south- southeast swell cannot be ruled out.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov