Hilo

Tonight: Occasional showers. Lows 64 to 70 near the shore to 54 to 59 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Friday: Occasional showers. Highs 77 to 83 near the shore to 62 to 67 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Friday Night: Mostly cloudy with numerous showers. Lows 63 to 70 near the shore to 54 to 59 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Kona

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 74 near the shore to 49 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 86 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 50 percent.

Friday Night: Partly cloudy with isolated showers. Lows around 73 near the shore to 49 to 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 25 mph. Chance of rain 70 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 64 to 83. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 25 mph. Chance of rain 70 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 64 to 83. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 75 near the shore to around 53 near 5000 feet. East winds up to 25 mph shifting to the northeast 10 to 20 mph after midnight. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 87 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly clear. Isolated showers in the evening. Lows around 74 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Occasional showers. Lows 64 to 70 near the shore to 54 to 59 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Friday: Occasional showers. Highs 77 to 83 near the shore to 62 to 67 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Friday Night: Mostly cloudy with numerous showers. Lows 63 to 70 near the shore to 54 to 59 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Partly cloudy. Breezy. Lows around 75 near the shore to 53 to 58 above 4000 feet. East winds up to 20 mph.

Friday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 83 to 90 near the shore to around 69 above 4000 feet. East winds up to 25 mph shifting to the north up to 15 mph in the afternoon. Chance of rain 20 percent.

Friday Night: Mostly clear with isolated showers. Lows around 74 near the shore to 52 to 57 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will continue into Friday with high pressure far to the north-northeast of the islands. Showers riding in on the trades will remain focused over the windward sides of the islands into the weekend. Trade winds will weaken this weekend as the high moves to the east, and fewer showers will be carried in. Another round of wet weather is expected next week.

Discussion

No big surprises with the weather today. Moderate to locally breezy trade winds continue due to the high pressure system to the far north-northeast. Showers will continue to be carried in on the trades and will remain focused over the windward sides of the islands. Most of the clouds and showers extend east of the Big Island, so expect more showers at the southern end of the state into Friday.
Heading into the weekend, the high will begin to move to the east, resulting in the pressure gradient over the islands weakening. This will lead to a bit of a downward trend in the winds, and could turn the winds a bit more east to east- southeasterly.
The GFS and ECMWF global models continue to be in good agreement with the surface and upper level features heading into the weekend. The high moving to the east, and mid-level ridging helping to stabilize the environment over the islands a bit leading to the downtrend in shower activity.
Beyond that there is still general agreement with the surface features in the deterministic global models, but vastly different handling of the mid and upper levels. These differences will be a factor in what ultimately pans out. There is general agreement that a cold front will approach from the northwest midweek, but differences in timing and how far down the island chain the front goes. Differences in the timing, placement and strength of the mid and upper levels will factor into the amount of rain, and the frequency of showers. This will also determine winter weather possibilities for the Big Island summits, and the possibility for thunderstorms. While the deterministic global models suggest thunderstorms midweek, the NBM probabilities are low, as expected with such variability in the models.
The forecast from Monday onwards has been modified to follow the NBM solution to best incorporate the ensemble and blend of the various solutions. The chance for snow has been added to the Big Island summits started Wednesday night, and there seems to be sufficient agreements with deep layered moisture and cold temperatures aloft to support such a solution. Additional refinements will likely be made as the event gets closer, and hopefully there is more agreement in the models.

Aviation

Moderate to locally breezy trades will gradually ease heading into the weekend. A plume of enhanced low level moisture moving across island chain will continue to bring an uptick in low clouds and showers mostly over windward and mauka areas through tonight, with isolated spillover to leeward sides. MVFR/IFR conditions are possible in any heavier showers. Shower activity should decline tomorrow as drier air filters in on the trades.
AIRMET Sierra is in effect for mountain obscuration for windward portions of Maui and the Big Island where most of the shower activity is concentrated. Will monitor to see if it needs to be expanded to other islands overnight.
AIRMET Tango is in effect for moderate low level turbulence lee of island terrain and will likely be needed through tonight.

Marine

Fresh to strong easterly trade winds will continue through Friday and a Small Craft Advisory remains in effect for the typical windier waters around Maui and the Big Island through Friday afternoon. Winds will then ease into the moderate to locally fresh range out of the east-southeast over the weekend and into early next week. An uptick in winds is expected towards the middle of next week as a front moves across the waters.
A small north-northeast swell will lower into Friday morning. An upward trend is expected starting Friday due to a storm force low centered over the western Bering Sea that showed a large swath of storm-force winds aimed at Hawaii within the 310-330 degree directional bands. Expect small, long period forerunners to arrive by Friday evening from the north-northwest, then build through the weekend with peak surf heights arriving by Sunday. Surf heights look to approach advisory levels for exposed north and west facing shores on Sunday.
Surf along east facing shores will remain rough through Friday due to the strong trades locally and upstream across the eastern Pacific. A slight downward trend is expected this weekend.
Surf along south-facing shores will remain small, with mainly a mix of short period southeast and background long period south swell energy.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov