Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny. Isolated showers in the morning. Highs 87 to 92 near the shore to around 78 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 72 near the shore to around 62 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Saturday: Sunny. Highs 86 to 92 near the shore to around 78 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 84 to 91. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 71 to 76. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 85 to 91. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 85 in the valleys to around 67 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 66 to 71 in the valleys to around 60 above 4000 feet. East winds 15 to 25 mph. Chance of rain 70 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 75 to 85 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 90. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 67 to 75. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 77 to 89. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 88. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 79. Northeast winds around 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 76 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure far to the north of the islands will keep breezy trades blowing for the next couple of days. As the high moves away to the west this weekend, the trades will weaken a bit, but remain locally breezy. A subtropical ridge building far north of the islands early next week will reinforce the trades. A trough aloft to the northeast of the islands will keep trade wind showers more active than usual for the next couple of days, but still favoring windward and mauka locations, during the nights and mornings. Drier air, with fewer showers and more sunshine, is expected to arrive about Sunday.

Discussion

A 1032 mb surface high is about 1400 mi N of Honolulu early this morning. The pressure gradient between this high and a moderately active ITCZ well to our south is maintaining breezy background trades. Both 12z soundings showed the trade wind inversion over the islands remains elevated, just over 9000 ft. The elevated inversion appears to be due to a weak trough in the mid-levels to the E and NE of the islands. As a result, scattered showers over the water are a little taller and more active than usual early this morning, focusing on windward and mauka locales. However, a couple of the showers have been tall enough to briefly make it over to lee sections before dissipating.
Over the next few days, the surface high far to the N will push west, and weaken, leaving a weaker subtropical ridge behind that will push S. By Mon morning the ridge should be about 500 mi N of Honolulu. Then, a new, stronger subtropical ridge will become established farther N by the middle of next week. Our trades will respond by dropping a notch early next week, but likely remaining on the low end of breezy levels, before rebounding toward the middle of next week at breezy to perhaps locally windy speeds.
The weak mid-level trough is expected to continue to keep the subsidence inversion elevated through the next couple of days. Patches of moisture riding in on the trades will bring scattered showers to the islands at times (mostly favoring, but not limited to, nights and mornings), with highest PoPs over windward and mauka locations. A shower or two will spread leeward at times. The models are showing significantly drier air advecting over the state, and possibly weak mid-level ridging over the islands, starting about Sunday, which should allow for a lower subsidence inversion and diminished coverage and intensity of trade wind showers. It's possible somewhat deeper moisture with enhanced trade wind showers return toward the middle of next week, as another mid-level trough develops, closer to the islands.

Aviation

Moderate to locally breezy trade winds will persist through the next 24 hours. Pockets of moisture in the trade wind flow will help to maintain showers across portions of the Hawaiian Islands through the next 24 hours. Showers will favor the windward and mauka areas, especially overnight into the morning hours, and then more isolated activity can be expected during the day. VFR conditions will generally prevail, but brief MVFR ceilings and visibilities are likely in passing showers.
AIRMET Tango for moderate low level turbulence to the lee of higher terrain remains in effect. Conditions are likely to persist through the next 24 hours.

Marine

Little change to the marine and surf forecasts this morning. High pressure to the north continues to bring fresh to locally strong trade winds to the region today and into tomorrow. As a result, a Small Craft Advisory (SCA) remains in effect for the typical windier waters near Maui County and the Big Island through Saturday afternoon. Winds are expected to during the end of the weekend, with moderate to fresh trade winds expected Sunday and Monday.
The current small long-period south-southwest swell is expected to ease today and into the weekend, with another similar southwest pulse arriving Sunday. Small surf will persist as a mix of background southeast trade wind swell and leftover medium-period southwest swell move through next week.
Surf along north and west facing shores may increase slightly over the weekend as a medium-period north-northwest swell arrives. A tiny, medium-period north swell is possible Tuesday into Wednesday, followed by a second, small longer-period pulse arriving Thursday. Otherwise, trade wind wrap into some northern exposures will be the only source for surf.
Rough surf along east facing shores will remain essentially unchanged through Saturday, followed by a slight decline Sunday and Monday.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov