West Kaua’i

Tonight: Mostly clear. Lows 71 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light.

Thursday: Mostly sunny with isolated showers. Highs 86 to 91 near the shore to around 78 above 3000 feet. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

Thursday Night: Mostly clear. Lows 71 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 83 to 91. East winds around 10 mph. Chance of rain 30 percent.

Thursday Night: Partly cloudy with isolated showers. Lows around 74. Northeast winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Partly cloudy with isolated showers. Lows 65 to 71 in the valleys to around 60 above 4000 feet. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 85 in the valleys to around 68 above 4000 feet. East winds around 10 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy with isolated showers. Lows 65 to 70 in the valleys to around 59 above 4000 feet. East winds around 10 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 66 to 75. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 79 to 88. East winds around 10 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy with isolated showers. Lows 66 to 74. East winds around 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy with scattered showers. Lows 65 to 78. East winds around 10 mph. Chance of rain 30 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 88. East winds around 10 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy with isolated showers. Lows 66 to 78. East winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Low pressure north of the islands will remain embedded in a broad, nearly stationary area of high pressure for the next several days, resulting in a hybrid sea breeze and moderate trade wind pattern. Hot and dry conditions will prevail with little to no rainfall expected.

Discussion

No significant changes to the forecast this afternoon. A surface low and its associated trough remain embedded within a broad, quasi- stationary high pressure ridge north of the islands. As a result, trade winds will continue to back off into the light to locally moderate speed range through the weekend. The atmosphere will remain very stable into next week thanks to broad high pressure and dry conditions in the mid levels. This is evident in the 00Z soundings from Hilo and Lihue this afternoon, with strong temperature inversions around 6500-7500 feet. Hot and dry weather will be the name of the game at the surface as well, with minimal rainfall expected for most locations.
Trade wind speeds reduce even more this weekend into early next week, resulting in a more widespread sea/land breeze pattern. This would enhance leeward and interior region cloud buildups in the afternoons. However, little to no precipitation is expected from any showers that do develop as a drier airmass moves in. Furthermore, temperatures are forecast to be quite high through the forecast period, upwards of 90 degrees in some areas, which could pose some elevated fire weather concerns (see latest fire weather section).
The latest deterministic model guidance from the GFS and ECMWF is in good agreement that the aforementioned low and associated trough will eventually lift northward next week. This will open the door for high pressure to rebuild to the north and may result in trades strengthening a bit around the middle of next week.

Aviation

A moderate, stable, and rather dry trade wind flow will ease slightly on Thursday, leading to an increase in afternoon sea breezes near leeward terrain. Periods of MVFR conditions will briefly affect windward slopes, and aside from isolated pockets of afternoon MVFR ceilings on leeward terrain, VFR will dominate over most leeward sections.

Marine

A ridge of high pressure north of the state will gradually shift southward throughout the week and stall just north of the state this weekend. This will cause the current moderate to locally fresh trade winds to weaken to gentle to moderate speeds over the weekend.
A small, long period south swell continues to slowly fill in this afternoon. Another reinforcing pulse should fill in Thursday and peak Friday near the summer average before declining over the weekend. Surf should return to background levels early next week along south facing shores.
A front located far northwest of the state had a fetch of strong winds directed at the islands during the daytime ASCAT pass today. This fetch should generate some small short-period waves out of the north-northwest this weekend into early next week. A stronger storm-force low developing near Kamchatka over the next few days should generate some longer period energy out of the northwest around September 2nd. This swell could generate surf near the September average during its peak. For the month of September the average surf heights along north facing shores is 4 to 6 feet (Goddard-Caldwell Database).
Small short-period surf along east facing shores will decrease on Thursday as winds locally and upstream ease through the weekend into early next week.

Fire weather

Low relative humidity values and hot conditions will continue through the first half of next week due to the arrival of a drier airmass. However, low wind speeds will keep us from reaching critical fire weather thresholds. By midweek next week, the broad high pressure ridge will rebuild, and may result in winds strengthening a bit, though still does not appear to reach critical thresholds at this time.

HFO Watches/Warnings/Advisories

None.

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