West Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 69 to 74 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Saturday: Sunny. Isolated showers in the morning. Highs 85 to 90 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Mostly clear. Lows 70 to 75 near the shore to around 62 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 74. East winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 70 in the valleys to around 60 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny with scattered showers. Highs 75 to 84 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 65 to 70 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 65 to 74. Southeast winds up to 15 mph. Chance of rain 50 percent.

Saturday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 87. East winds up to 15 mph. Chance of rain 40 percent.

Saturday Night: Partly cloudy with isolated showers. Lows 66 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 65 to 76. Northeast winds up to 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 86. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 66 to 77. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Surface high pressure will remain anchored far northeast of the state through next week. Showers will favor windward and mauka areas, especially during the overnight through early morning hours. Over the weekend, trades will increase and much drier air will move into the region. More typical trade wind weather will commence early next week as batches of moisture filter in on the moderate to locally breezy trade winds.

Discussion

This afternoon's visible satellite imagery shows sparse incoming open-celled cumulus clouds immediately upstream of the main Hawaiian Islands that will continue to filter in on the trades and bring brief periods of clouds and showers to windward and mauka areas. In addition, clouds have built up over some leeward slopes, especially over the Big Island. Just beyond the remaining open- celled cumulus clouds, a large area of closed-cell cumulus can be seen moving westward on the trades, which is indicative of the drier, more stable airmass that is expected to move overhead this weekend.
Surface high pressure will remain anchored far northeast of the state through the end of next week and drive trade winds with periodic showers across the region through the forecast period. Embedded in the southwest flank of this surface high, a weak low level trough (best seen at 700 mb) is passing over Hawaii this afternoon with rather inconsequential impacts to our local weather, as the surface reflection is quite weak. If anything, as the axis of this weak trough continues to move across the western end of the state this evening, we might see a slight uptick in clouds and few more showers moving into windward areas of Oahu and Kauai through tonight…but the available atmospheric moisture looks to be limited.
The surface high will build over the weekend, strengthening the local pressure gradient and bringing breezy trade winds across the island chain. With the drier, more stable airmass moving overhead, low subsidence temperature inversion heights in the 4,000 to 5,000 foot range are forecast, limiting cloud and shower development tomorrow through Sunday. The combination of lower humidity levels due to the drier air mass and breezy trade winds will elevate fire concerns across the state on Sunday.
Wind speeds will drop back to more moderate to locally breezy levels from Monday onward as the high weakens slightly. Batches of moisture will filter in on the trades and bring periods of showers to windward and mauka areas through next week.

Aviation

High pressure remiains in place north of the Islands today and will continue to produce moderate to locally breezy trade winds (10 to 15 kt). Isolated showers are also possible on the windward and mauka parts of each island.
No AIRMETs are currently in effect.

Marine

A nearly stationary high pressure system northeast of Hawaii will continue to drive moderate to locally strong trades across the local waters for the next couple of days. The Small Craft Advisory (SCA) for typically windier waters and channels near Maui and the Big Island remains in effect through Saturday afternoon. Trade winds speeds are forecast to increase over the weekend as the high strengthens, which will likely require the extension and potentially the expansion of SCA conditions across the Hawaiian waters later this weekend into early next week. Trade wind speeds could then decrease slightly by middle of next week.
The current small, long-period, south swell will gradually ease into the weekend, dropping south shore surf to below average. Back to back pulses of slightly larger south swells are possible starting Monday, which could build surf near to above advisory levels (10 ft) along south facing shores as early as Monday night into Tuesday,then remain near to above average through much of next week.
Rough and choppy conditions will continue along east facing shores, then likely pick up a bit Sunday into early next week as winds strengthen. Surf will remain very small along north facing shores.

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.

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