Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 84 near the shore to around 74 above 3000 feet. East winds up to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 71 near the shore to around 57 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 85 near the shore to around 75 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs around 82. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs around 83. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy with scattered showers. Highs around 77 in the valleys to around 66 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 60 in the valleys to around 52 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs around 78 in the valleys to around 67 above 4000 feet. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 77 to 83. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 78 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy with scattered showers. Highs 75 to 81. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 58 to 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 76 to 82. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate trade winds will persist into Sunday, followed by an extended period of moderate to breezy trade winds early next week. A weak upper-level trough will move across the islands during the next couple of days. High clouds will continue to stream up over most of the state during the next day or two as this feature arrives. In addition, there will likely be a slight uptick in windward and mauka showers starting late tonight or Sunday, and continuing into early next week.

Discussion

A surface ridge appears to be less than 500 miles north of Honolulu. Elsewhere, a cold front, which is about 325 miles northwest of this ridge, is moving rapidly toward the south- southeast at about 20 mph. As a result, the ridge has been weakening since last evening. This is causing the pressure gradient to relax across the main Hawaiian Islands early this morning. Therefore, the trade winds have weakened to light to moderate speeds overnight.
The axis of a weak upper-level trough, which appears to be about 370 miles west-southwest of Lihue, is moving eastward at 15 to 20 mph. The south to southwest flow aloft along the eastern periphery of this feature continues to transport broken to overcast high clouds up over the state. Otherwise, stable atmospheric conditions persist with a low-level trade wind inversion around 6 thousand feet, while the precipitable water values range from 1.2 to 1.3″. Radar reflectivity data show some of the upper-level moisture related to the high clouds, but little significant precipitation from these clouds is actually reaching the ground. There are also light trade showers evident over some windward sections of the island chain, especially portions of the eastern Big Island.
The forecast models continue to show the surface ridge north of the islands will weaken and be displaced southward as the cold front moves down toward it during the next 12 or so hours. This will result in additional relaxation of the pressure gradient across the area, so expect even weaker trade winds by this evening. The weaker low-level trade wind flow will continue to deliver low clouds and light trade showers into some windward and mauka sections. The weak upper-level trough west-southwest of Kauai is expected to eventually be just south of smaller islands. The flow aloft along the eastern periphery of this feature will continue to carry variable amounts of high clouds across most of the state. As this trough aloft continues to move closer to the Big Island Sunday, it may cause some weak instability to develop, especially over the eastern end of the island chain. There may be some increase in the coverage of low clouds and showers. In addition, the current forecast indicates there is a slight chance of thunderstorms Sunday afternoon for the upslope sections of the leeward Big Island.
Heading into next week, a broad surface high pressure system is expected to build in far north of the state, This will push the frontal boundary down to a point 200 to 300 miles north of the islands, where it will likely stall and weaken. At the same time, the pressure gradient will tighten across the area, which will cause the trade winds to become locally breezy starting Sunday night or early Monday. The upper-level trough is also expected to linger in the vicinity of the eastern end of the island chain. This will likely keep trade showers moving over most windward and mauka sections. The gusty trades may also allow a few brief showers to reach leeward sections of some of the smaller islands, especially during the late night and early morning hours. In addition, expect clouds and showers to develop over the upslope sections of the leeward Big Island each afternoon. Looking ahead, the forecast models appear to show a weak surface trough developing to the east of the state by Thursday. Assuming this feature does form, it may drift slowly westward toward the state from Friday into next weekend. This scenario may result in a slight increase in low-level moisture, along with the potential for some weakening of the trade winds late next week.

Aviation

High pressure north of the islands will maintain light to moderate trade winds over the region for most of the weekend. High clouds are streaming over the islands from the southwest in the upper level wind flow associated with an upper level low to the southwest of the islands. These high clouds are beginning to thin as the upper level low is weakening, and this trend is expected to continue today. AIRMET Zulu has mention of light icing due to these high clouds, but expect this to be dropped later this morning as the high clouds continue to thin.
AIRMET Tango is in effect for moderate upper turb over the entire area as a result of the upper level winds associated with the upper level low mentioned above. Unlike the high clouds, the upper level winds haven't started to show a downward trend, so expect the AIRMET to remain in place into Saturday.
AIRMET Tango had been in effect for low level turbulence, however as the VAD wind profile continued to show lighter winds over the state, it was dropped around midnight. Not expecting to see a need for another AIRMET Tango through much of Sunday.
VFR conditions are expected to prevail across the state, with some MVFR conditions possible in showers which will be focused over the windward and mountains areas in the trade wind flow.

Marine

A high pressure ridge axis just north of the state will be moving south southeast and into the area this weekend as a cold front approaches from the north. The front passing north of the state will assist in holding moderate winds in place through Sunday afternoon. High pressure building in behind the front early next week will re-tighten the upstream pressure gradient and this will result in a return of fresh to locally strong trades. Strong high pressure building north of the area behind the front will reintroduce Small Craft Advisory (SCA) conditions across the notoriously windier zones surrounding Maui County and Big Island late Sunday. Strengthening trades to SCA magnitudes are forecast to expand westward across the majority of the remaining marine zones by Monday night.
East-facing shore surf will subtly subside this weekend in response to the aforementioned vicinity ridge axis and resultant lighter east trades. Surf along eastern exposures will again become more rough and choppy through most of next week as fresh to locally strong trades make a comeback. Several days of a fresh to locally strong trade fetch over and upstream of the islands may push elevated surf along eastern facing shores to just under the High Surf Advisory thresholds by Wednesday. No north swell equates to a near flat weekend along many north and west-facing shores. The only exception will be along more eastern facing exposures that will receive some trade wind swell wrap. A moderate size, medium period north (350 degrees) swell will arrive Monday, and peak surf along north-facing shores Tuesday. South surf will remain small for the foreseeable future as very small, short period background southeast to southwest swells roll in.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov