West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 65 to 70 near the shore to around 58 above 3000 feet. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Sunny. Isolated showers in the morning. Highs 81 to 86 near the shore to around 71 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly clear. Lows 65 to 70 near the shore to around 58 above 3000 feet. East winds around 10 mph.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 68. East winds 10 to 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 84. East winds 10 to 15 mph. Chance of rain 30 percent.

Thursday Night: Partly cloudy. Scattered showers after midnight. Lows around 68. East winds 10 to 15 mph. Chance of rain 30 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 60 to 66 in the valleys to around 56 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Thursday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 72 to 81 in the valleys to around 63 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 61 to 66 in the valleys to around 56 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 62 to 69. East winds around 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 83. East winds 10 to 15 mph. Chance of rain 30 percent.

Thursday Night: Partly cloudy. Scattered showers after midnight. Lows 62 to 69. East winds 10 to 15 mph. Chance of rain 30 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 72. East winds around 10 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 83. East winds 10 to 15 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 72. East winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A weakening upper level low to the northeast of Kauai will continue to weaken over the next several days. A more stable airmass will gradually settle over the islands during this time. Trade winds will focus clouds and showers over windward and mountain areas. An approaching front this weekend will bring another period of weaker winds, and an increase in showers as it moves down the island chain during the first half of next week.

Discussion

No changes to the forecast were made with the afternoon package. Showers continue to be carried in on the trade wind flow, and with the somewhat unstable airmass overhead, some of those showers are briefly heavier than normal.
With the global models in decent agreement through the forecast period, with the high resolution models in general agreement in the short term, the forecast largely follows the National Blend of Model.
Water vapor imagery shows the upper level low to the northwest of Kauai this afternoon, and the associated upper level trough extending to the south-southwest from the low. Thunderstorms continue to fire off near the upper level low and the along the the trough. These thunderstorms extend into the offshore waters to the west of the main Hawaiian islands, with a few near the coastal waters over the last few hours. With the upper level feature weakening, chances continue to lower for any development closer to the islands.
The upper level wind flow on the east side of the upper level system is driving upper level clouds over the islands from Oahu eastward. This upper level feature is also bringing some instability to the islands, and we have seen instability helping to enhance the showers riding in on the trade wind surface flow.
The ECMWF and GFS are in good agreement with the upper level low continuing to weaken into a mid-level trough over the next 24 hours, while remaining nearly stationary. By Friday morning, little remains of the mid level feature, while an upper level trough remains in place. By Saturday morning, mid to upper level ridging pushing in from the west will help to provide some more stability to the region. A surface front approaching the islands from the northwest on Sunday is not expected to have as much upper level support. The cloud and shower band associated with the front is expected to reach Kauai Sunday night, reaching the central islands by Monday afternoon, and slowly moving towards the Big Island Tuesday. The GFS and ECMWF have become better aligned in the handling of this front over the past several model runs, and thus using the National Blend of Models seemed the best course of action.
A drier airmass will move in behind the front, along with a new high far northwest of the islands. The new high will move to the east around 30N as the front moves down the island chain. This will bring a return to more typical trade winds behind the front.

Aviation

Moderate to breezy easterly trade winds will prevail across the island chain through tomorrow. Afternoon radar and satellite imagery show low clouds and showers continuing to move into north through southeast sections of the islands. As such, AIRMET Sierra remains in effect for mountain obscuration across windward areas of all islands. This general pattern will persist over the next couple of days, with variations in the amount of moisture being brought in on the trades.
Additionally, a band of thick high-level cirrus clouds associated with the subtropical jet currently stretches over the island chain. Model guidance suggests that areas of moderate upper level turbulence, at about 30,000 feet and higher, will be possible at least through tomorrow. Therefore, AIRMET Tango remains in effect area-wide. It is possible that a SIGMET for severe upper level turbulence may be needed sometime this evening, particularly over or near the western islands.

Marine

Surface high pressure will remain anchored northeast of the state through Thursday and help maintain fresh to locally strong trades across the islands. Thus, a Small Craft Advisory is in effect through Thursday afternoon across the typically windy waters surrounding Maui County and Big Island. A front approaching from the northwest will allow trades to gradually weaken Friday into Saturday, becoming light and variable statewide Sunday. Winds shift north northeasterly by early next week as the frontal system presses southeastward over the islands.
A 4 to 5 foot, 14 to 16 second, northwest swell can be noted at the nearshore buoys this afternoon. This swell will slowly lower tonight into Thursday with a similar sized swell poised to affect the local waters by Friday. These swells will produce elevated surf, though still well below High Surf Advisory, for north and west facing shores. A large, possibly extra large, northwest swell originating from a storm force low off the coast of Japan will likely reach the islands Sunday or Monday. This late season, long period, swell may produce warning level surf along the smaller island north and west-facing shores when it reaches the state early next week.
Expect east shore surf to remain elevated and choppy the next several days as winds strengthen over and upstream of the state. South shore surf sets will hold at average waist high heights with the passage of a couple of very small, long period south swells.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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