Hilo

Tonight: Cloudy. Occasional showers in the evening, then numerous showers after midnight. Lows 63 to 68 near the shore to 48 to 55 at 4000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Thursday: Mostly cloudy with scattered showers. Highs 75 to 81 near the shore to around 64 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 62 to 68 near the shore to 48 to 53 at 4000 feet. Northeast winds up to 10 mph shifting to the northwest around 10 mph after midnight. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy. Isolated showers in the evening. Haze through the night. Lows around 71 near the shore to 45 to 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Thursday: Partly sunny. Haze through the day. Scattered showers in the afternoon. Highs 81 to 86 near the shore to around 65 near 5000 feet. East winds up to 10 mph shifting to the west around 10 mph in the afternoon. Chance of rain 50 percent.

Thursday Night: Partly cloudy. Isolated showers in the evening. Haze through the night. Lows around 71 near the shore to 44 to 51 near 5000 feet. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Breezy. Partly sunny with isolated showers. Highs 72 to 79 near the shore to 68 to 77 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy. Breezy. Isolated showers after midnight. Lows 61 to 69 near the shore to 53 to 59 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Breezy. Partly sunny with isolated showers. Highs 72 to 79 near the shore to 68 to 77 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy. Breezy. Isolated showers after midnight. Lows 61 to 69 near the shore to 53 to 59 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy and haze. Lows around 72 near the shore to around 50 near 5000 feet. East winds 10 to 20 mph.

Thursday: Breezy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 83 near the shore to around 64 near 5000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

Thursday Night: Partly cloudy. Breezy. Haze through the night. Lows around 71 near the shore to around 48 near 5000 feet. East winds 10 to 20 mph.

Puna

Tonight: Cloudy. Occasional showers in the evening, then numerous showers after midnight. Lows 63 to 68 near the shore to 48 to 55 at 4000 feet. East winds up to 10 mph. Chance of rain 90 percent.

Thursday: Mostly cloudy with scattered showers. Highs 75 to 81 near the shore to around 64 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 62 to 68 near the shore to 48 to 53 at 4000 feet. Northeast winds up to 10 mph shifting to the northwest around 10 mph after midnight. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly cloudy. Isolated showers in the evening. Haze in the evening. Lows around 72 near the shore to 49 to 55 above 4000 feet. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 81 to 87 near the shore to 64 to 70 above 4000 feet. East winds 10 to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Thursday Night: Partly cloudy. Haze. Lows around 71 near the shore to 48 to 54 above 4000 feet. East winds 10 to 15 mph.

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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Data Courtesy of NOAA.gov