West Kaua’i

Tonight: Partly cloudy with a 20 percent chance of showers. Lows 66 to 71 near the shore to around 59 above 3000 feet. Northeast winds 10 to 15 mph.

Sunday: Mostly sunny with a 20 percent chance of showers. Highs 81 to 87 near the shore to around 73 above 3000 feet. East winds 10 to 15 mph.

Sunday Night: Partly cloudy with isolated showers. Lows around 69 near the shore to around 60 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with a 50 percent chance of showers. Lows around 69. Northeast winds 15 to 20 mph.

Sunday: Breezy. Partly sunny with showers likely in the morning, then mostly sunny with chance of showers in the afternoon. Highs 78 to 86. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 70. Northeast winds around 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Chance of showers in the evening, then showers likely after midnight. Lows 60 to 68 in the valleys to around 57 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Sunday: Partly sunny. Showers likely in the morning, then chance of showers in the afternoon. Highs 72 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy with frequent showers. Lows 60 to 69 in the valleys to around 58 above 4000 feet. East winds around 15 mph. Chance of rain 90 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with a 50 percent chance of showers. Lows 63 to 70. East winds 10 to 20 mph.

Sunday: Partly sunny in the morning then becoming mostly sunny. A 50 percent chance of showers. Highs 73 to 84. East winds 10 to 15 mph.

Sunday Night: Mostly cloudy. Showers likely in the evening, then frequent showers after midnight. Lows 62 to 70. East winds 10 to 15 mph. Chance of rain 90 percent.

East Kaua’i

Tonight: Mostly cloudy with a 50 percent chance of showers. Lows 63 to 73. Northeast winds 10 to 15 mph.

Sunday: Partly sunny with a 50 percent chance of showers. Highs 71 to 83. Northeast winds 10 to 15 mph.

Sunday Night: Mostly cloudy with frequent showers. Lows 64 to 73. Northeast winds around 15 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

Surface high pressure located far north of the state will maintain a tight enough pressure gradient across the islands to produce breezy to locally windy trades the next several days. A generally dry start of the week with showers primarily focusing along windward exposures. A weak boundary will hang around north of the state into early next week before sagging south and meandering across the islands through next week. This will introduce increased cloud cover and shower frequency within an established trade wind regime.

Discussion

The diffuse boundary that was draped across the western third of the state early this morning has lifted north and trades have filled in behind it. While not entirely discernible in the larger synoptic scale, there will be just enough of a sheared boundary on the southern tail of this boundary's remnants to promote higher frequency of showers across a larger area from the Kauai Channel northwest. Afternoon soundings are hanging onto a fairly deep and moist, 9-10k foot boundary layer. A signal that, with the weak boundary not too far off in the distance, more rich mid level moisture streaming in on better established trade flow will likely focus on Kauai and its surrounding waters through tomorrow morning. As evidenced in today's VAD wind profiles and various surface observations along the slopes of Haleakala and Maui's central valley, trades peaked at high end breezy with localized windy gusts. The tight pressure gradient over the islands from strengthening surface high pressure centered far northwest of the area will guarantee that early week trades remain breezy to locally windy across exposed high terrain and more efficiently funneled through valleys and channels through Tuesday. Today's precipitation numbers were greatest across the north and east facing mauka slopes of Kauai. This will remain the case the next several days as the aforementioned boundary begins to drift southward and settles over the state. This boundary will not only increase shower chances but will disrupt the gradient just enough across the islands to allow trades to fall back to gentle to breezy speeds by Tuesday morning.
Lower mid to upper level heights will begin to rise into Monday as the center of upper level ridging builds in over the islands from the northwest. This will generally provide enough stability to keep the majority of tomorrow and Monday dry. However, as this diffuse boundary to the north sags south and into the central islands going into the middle of next week, most of the island chain will experience thicker low clouds and periods of intermittent precipitation each subsequent day. This shear line will provide a pathway for mid level moisture to ride in on. With little movement of this boundary, this more wet (than not) areawide pattern will hold for several days.
A much improved day as it relates to the downstream transport of Kilauea's volcanic emissions. CIMSS natural color daytime satellite imagery verifies a much clearer day. Reasoning is that trades have returned and therefore fine particulates will be better transported away from the islands and/or mix out. Winds will hold at breezy magnitudes the next several days so haze/vog will not be as much of an issue as in previous days.

Aviation

Breezy trade wind weather is expected across most of the state with passing low clouds and scattered showers over windward and mountain areas through Sunday. The one exception is over on Kauai, where we have a plume of moisture that is producing frequent trade wind showers along windward and mountain areas. Periods of MVFR conditions will be possible with the showers on Kauai and even brief periods of IFR conditions can't be ruled out with the heavier showers. Showers should become less frequent later tonight into Sunday.
AIRMET Sierra remains in effect for mountain obscuration on Kauai. AIRMET TANGO is also in effect for low level turbulence downwind of terrain due to the breezy trade winds across the state.

Marine

Rough marine conditions will prevail through the weekend, and a Small Craft Advisory (SCA) is in effect for almost all Hawaiian waters. A strong 1033 mb high will remain centered about 850 nm northwest of Kauai into Monday and will drive fresh to strong trade winds, especially over the typically windy waters around the Big Island and Maui County. Trades will likely ease slightly late Monday and Tuesday as the surface high weakens, but trades are expected to build again Wednesday and Thursday.
An extra large, long-period north (350 deg) swell will peak tonight and early Sunday. This swell has come in at 3 to 4 feet above guidance at buoy 51001, where measurements of 14 to 17 feet at 15 to 17 seconds have been recorded during the past couple of hours. Surf will continue to rise into the evening and remain at High Surf Warning levels through much of Sunday along north and exposed east facing shores and at High Surf Advisory levels along west facing shores from Kauai to Maui. In addition, moderate to heavy surges are anticipated in north facing harbors through Sunday and likely into Monday. The large swell will also produce combined seas in excess of 10 feet over most waters and will contribute to the need for a SCA through Sunday night and possibly Monday. The north swell will steadily decline Sunday night and Monday and will fade by the middle of next week.
Small surf will prevail along south facing shores through early Sunday. Small pulses of south swell are possible late Sunday and Monday and again midweek.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Sunday for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Kauai East, Koolau Windward, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
High Surf Advisory until 6 PM HST Sunday for Kauai Leeward, Waianae Coast, Maui Leeward West, Molokai West.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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