Photo Credit: Brendan Stephen

West Kaua’i

Rest Of Today: Mostly sunny with isolated showers. Highs around 84 near the shore to around 72 above 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 70 near the shore to around 59 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs around 84 near the shore to around 72 above 3000 feet. North winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Today: Partly sunny with scattered showers. Highs around 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows 66 to 71. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs around 81. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Rest Of Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78 in the valleys to around 62 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 59 to 64 in the valleys to around 52 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78 in the valleys to around 62 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Rest Of Today: Partly sunny with scattered showers. Highs 74 to 84. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 70. East winds up to 15 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 84. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Rest Of Today: Partly sunny with scattered showers. Highs 74 to 83. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 72. Northeast winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 74 to 83. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Today through Friday, moderate to locally breezy trade winds will continue across the island chain. Showers will generally favor windward and mauka areas throughout this period in addition to sheltered interior and leeward sections of the islands each afternoon (especially on the Big Island). Trades are expected to weaken this weekend, but will return to moderate to locally breezy speeds by the middle of next week.

Discussion

Early this morning, a weakening upper-level low remains situated just northeast of the main Hawaiian Islands with upper troughing extending to the north and northwest. Southwesterly flow aloft across the island chain is streaming high level cirrus clouds over the eastern half of the state. Meanwhile, at the surface, high pressure is centered about 1,000 miles north-northeast of Oahu, which will steer moderate to locally breezy easterly trade winds across the island chain over the next couple of days.
Observed 12z soundings and Lihue and Hilo show little to no trade wind inversion and precipitable water values a bit higher than the normal range for this time of year. Nevertheless, latest satellite and radar imagery shows only isolated to scattered showers favoring windward and mauka locations early this morning. A relatively unremarkable amount shower activity is observed in the coastal waters upstream of the islands, though there are some cooler cloud tops noted on satellite associated with a band of moisture located further east within the offshore waters.
The overall weather pattern will remain similar through Friday. The weak upper low just northeast of the islands will provide just enough instability to block formation of a capping trade wind inversion, allowing showery low clouds to build taller and perhaps bring some moderate to locally heavy showers from time to time, particularly across windward and mountain areas. Additionally, convergence over the Big Island will increase clouds and showers over interior and leeward slopes there as well each afternoon. With that said, models continue to show a slight warming of 500mb temperatures each afternoon from today onward over the Big Island. Model thunderstorm probabilities also trend lower from today through the weekend. Therefore, continue to think that the thunderstorm potential for the rest of the week into the weekend will be rather low, so have excluded it from the forecast at this time.
A front passing north of the islands will erode the high pressure north of the state beginning this weekend, which will diminish surface trade wind flow across the state. With slightly weaker trades, sea breezes could develop Saturday and Sunday afternoons. With this morning's forecast updates, wind speeds for the weekend were trended down based on latest model guidance, but have held off for now on going quite as low for background wind speeds as the ECMWF would suggest. Latest thinking is that while trades will be weak enough for afternoon sea breeze-induced clouds and showers over island interiors and leeward locations (especially on Sunday), light to moderate trades will continue to provide windward and mauka areas with occasional showers throughout the weekend as well.
Relatively light to moderate trades may persist into the first part of next week, though trade winds should increase once again around the middle of the next week as troughing aloft and at the surface to our north begins to move eastward away from the islands.

Aviation

Moderate trades within a marginally unstable environment will continue through the period and will favor a hybrid sea breeze pattern in the afternoon. Periodic showers, locally heavy, will mainly affect windward and mauka zones during this time. The most sheltered leeward areas may also see a period of afternoon showers. VFR is forecast to prevail, however high moisture content in the lowest levels guarantees transient periods of MVFR, especially in the early morning and overnight. Expect IFR within any heavy showers.
Conditions will be monitored for the potential AIRMET Tango for moderate mid/upper turb as an 80 to 100kt subtropical jet remains in place over the islands.
No AIRMETs in effect at this time.

Marine

A 1029 mb surface high far N of the islands will shift E and weaken the next couple of days as a slow-moving and relatively weak low pressure system passes well N of the area. Moderate to locally fresh trade winds will continue into Friday, strongest in the afternoons as heating of the islands leads to localized acceleration of the flow. Light to locally moderate trade winds are expected over the weekend, and may trend stronger early next week. However, model guidance has been trending toward light winds lingering as the low may be slow to depart.
No significant swells are expected into next week. Small pulses of swell from the SSW are possible this weekend, and from the S early next week. There's also the outside chance of a small NW swell around the middle of next week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov