Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Sunny with isolated showers. Highs around 90 near the shore to around 78 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 72 near the shore to around 63 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny with isolated showers. Highs 87 to 92 near the shore to around 78 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 85 to 92. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 74. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 85 to 92. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 75 to 86 in the valleys to around 68 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 75 to 85 in the valleys to around 67 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 90. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers. Lows 67 to 75. East winds 10 to 15 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with scattered showers. Highs 78 to 89. East winds 10 to 20 mph. Chance of rain 40 percent.

East Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 88. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 79. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 76 to 88. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Expect breezy trade winds to persist during the next couple of days. Low clouds and showers carried by the trades will continue to favor windward and mauka areas, especially during the nighttime and morning hours. Cloud buildups and spotty showers will also be possible along the upslope sections of the leeward Big Island each afternoon and evening. Patches of high clouds will move rapidly across island skies at times through Friday. The trade winds may weaken slightly from Sunday into early next week.

Discussion

A 1028 mb surface high pressure system is centered near 41N 140W, or almost 1700 miles northeast of Honolulu. There is also a 1033 mb surface high pressure system located near 44N 169W, or about 1700 miles north-northwest of Honolulu. The tight pressure gradient south of these features is maintaining locally breezy easterly trade winds across the main Hawaiian Islands early this morning. Elsewhere, the axis of an upper-level trough appears to be about 1100 miles west-northwest of Lihue. The flow around the eastern flank of this feature is transporting patches of cirrus clouds up over portions of the state from the southwest. The latest loops of satellite imagery and radar reflectivities show scattered to broken low clouds with embedded isolated light showers moving from east to west into the windward facing sections of many of the islands.
The forecast guidance indicates the locally breezy trade winds will continue to transport low clouds and brief showers into the windward sections of the islands this morning. The surface high, which is currently far northeast of the area, will shift eastward, and gradually weaken today as a front far north of the state tracks toward the east-southeast. At the same time, the second surface high described above will build far north of the state as it moves toward the southeast at 15-20 mph. This will cause the gradient to tighten over the region, which will likely produce breezy trade winds from later today and tonight through Friday.
The forecast models continue to show a weak upper-level low may move down from the northeast toward the area during the next few days. This may cause the trade wind inversion to erode slightly starting tonight or Friday, which may may produce some slight atmospheric instability over the state into this weekend. If there are pockets of moisture moving under this low, there may be a slight enhancement of low clouds and trade showers. These trade showers will generally favor windward and mauka areas, especially during the nighttime and morning hours. Cloud buildups and isolated showers will also be possible along the upslope sections of the leeward Big Island each afternoon and evening. In addition, some patches of high clouds may continue to stream above the state during the next couple of days, especially the western islands, as the upper-level trough propagates slowly westward away from the region.
Looking ahead, the latest model guidance continues to show a surface front pushing down from the north, which may weaken the surface ridge north of the state later this weekend. This scenario would cause the trade winds to weaken into the moderate range by Sunday. Therefore, the current forecast continues to maintain a fairly typical trade wind weather pattern from Sunday into early next week. The trades may become locally breezy again starting next Tuesday.

Aviation

Moderate to locally breezy trade winds will strengthen slightly heading into this afternoon and evening. Showers embedded in the trade wind flow will favor windward and mauka areas, but an occasional shower may spillover into leeward locations. Shower activity will be most active during the overnight to mid morning hours. VFR conditions will generally prevail, but brief MVFR ceilings and visibilities are likely in any passing showers.
No AIRMETs are in effect.

Marine

Fresh to strong easterly trade winds will persist through Saturday, and a Small Craft Advisory (SCA) remains posted for the typical windy areas around the Big Island and Maui County. This advisory may need to be expanded to other waters tonight through Saturday as high pressure builds to the north. Guidance does depict a weakness forming in the ridge far north-northeast of the area by the end of the weekend, which could result in the trades easing slightly Sunday through Monday.
Surf along south facing shores will remain around and just below the seasonal average through the weekend as southwest swells move through. Observations at the buoys reflect a long-period south- southwest swell moving through this morning. This swell will linger today, then ease Friday into the weekend. A similar southwest pulse is expected Sunday through early next week. For the extended, expect the small surf to persist with mainly a mix of background southeast trade wind swell and leftover medium- period southwest swell moving through next week.
Surf along north and west facing shores could come up slightly over the weekend as a medium-period north-northwest swell arrives. A tiny, medium-period north swell is possible Tuesday into Wednesday from a broad gale forecast to develop over the Gulf of Alaska this weekend. Strong- to near-gale force north-northeast winds on the backside of this broad system could send a second, small longer-period pulse out of the north-northeast early next week that would arrive 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