West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 68 near the shore to around 57 above 3000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 80 to 87 near the shore to around 71 above 3000 feet. Light winds. Chance of rain 20 percent.

Saturday Night: Mostly cloudy. Isolated showers in the evening. Lows around 67 near the shore to around 57 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 67. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny. Isolated showers in the morning. Highs 80 to 86. East winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Saturday Night: Mostly cloudy. Lows around 67. Light winds.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 61 to 66 in the valleys to around 55 above 4000 feet. Light winds. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 73 to 83 in the valleys to around 64 above 4000 feet. Light winds. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 61 to 66 in the valleys to around 55 above 4000 feet. Light winds. Chance of rain 30 percent.

North Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 62 to 69. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 75 to 82. Light winds. Chance of rain 20 percent.

Saturday Night: Mostly cloudy. Isolated showers in the evening. Lows 62 to 69. Light winds. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 61 to 71. Light winds. Chance of rain 50 percent.

Saturday: Mostly sunny with isolated showers. Highs 74 to 85. East winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy. Isolated showers in the evening. Lows 62 to 71. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Light to moderate southeasterly winds are expected to persist through the weekend. Light showers will focus across east to southeast slopes of each island during the overnight hours and over leeward and interior areas during the afternoon hours. A deep low pressure system will approach the islands early next week and bring southerly winds to the area, drawing up tropical moisture that may increase rain chances across the western end of the state.

Discussion

This afternoon's radar and satellite imagery show clouds across all island interiors, with scattered showers over Oahu and isolated showers across the other island interiors. The 00Z (2 PM HST) upper air soundings show that the strong temperature inversion is still in place over Hilo and Lihue this afternoon, but it has lifted to about 8,500 ft and 10,500 ft respectfully. While the inversion is still rather pronounced, low-level moisture and instability have been sufficient below this layer to produce some showers across the area. The high resolution model guidance from this morning has verified pretty well this afternoon in regard to this shower activity. In addition, a convergent boundary can also be seen on satellite and radar as it slowly approaches Kauai from the west. This weak boundary and its associated moisture may help to increase shower activity across Kauai this evening.
A light to moderate southeast flow is expected to persist across the state through at least Saturday as the surface ridge remains overhead. In this pattern, clouds and showers will generally favor east and southeast facing slopes and coasts overnight into the morning hours, then transition to leeward and interior areas by the afternoon as sea breezes develop. Convergent boundaries downstream of island terrain may also occasionally help to bring clouds and showers to leeward areas in the afternoon/evening hours. However, with mid-level ridging overhead, shower activity should be limited through the weekend.
By late Sunday or Monday, the transition to a more southerly flow across the western half of the state will begin as a strong low pressure system stalls to the northwest and its attendant northeast to southwest oriented frontal boundary gradually approaches and then also stalls. These southerly winds will help to draw up tropical moisture across the western end of the state, which combined with the upper level troughing lifting inversion heights, may help to enhance shower activity over Niihau, Kauai and Oahu through the first half of next week. Islands over the eastern half of the state in Maui and Hawaii Counties will see little change to this fairly stable weather pattern through midweek, with the exception of a slight shower enhancement along the east and southeast slopes in the afternoon and evening hours. High clouds will also periodically blanket portions of the state as an upper level jet streak dips down and edges over the state.
However, it's worth noting that beyond Monday, forecast confidence remains on the lower end as the global models continue to struggle to get in sync with each other on the progression of this low pressure system as it interacts with another developing low to its northeast.

Aviation

A surface ridge remains over the islands, with a mostly dry and stable airmass in place. Light winds across the islands have produced afternoon sea breezes with clouds and limited showers over the interior of the islands. Expect overnight land breezes to clear out most of the clouds, except for some clouds moving in on the light east to southeast background flow. These clouds and showers will be focused over the windward and southeast-facing slopes, mainly overnight and during the early morning hours.
VFR conditions are expected to prevail, however the afternoon clouds and showers may bring some occasional MVFR conditions that could warrant the issuance of a mountain obscuration AIRMET Saturday afternoon.

Marine

A surface ridge will remain near or just N of the islands through the weekend. This will keep light to moderate E-SE winds with diurnal land and sea breezes in place through the next few days. A developing surface low and front far northwest of the islands is expected to strengthen this weekend and move east, and is expected to bring more southerly winds by Monday. Model discrepancies exist regarding the strength of the southerly winds due to the strength and position of the low. The front associated with this low may progress far east enough to enter the western coastal waters later next week, however forecast confidence remains low as the global models struggle to find a consensus.
A small, medium-period NNE swell will peak tonight near 4 feet 12 seconds, then gradually diminish through Sunday. A small WNW swell may also arrive over the weekend. More medium-period N swell is anticipated from Tuesday through Thursday next week. A small to moderate W swell is also possible around the beginning to middle of next week as the westerly winds associated with the low to the northwest could point towards the islands. Confidence on timing and size is low due to model differences in the handling of the low.
A small, long- period SSW swell is expected to continue providing small surf to S facing shores into next week.

HFO Watches/Warnings/Advisories

None.

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