Hilo

Tonight: Partly cloudy with isolated showers. Lows 59 to 67 near the shore to 50 to 56 at 4000 feet. Light winds becoming west up to 10 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the morning. Highs 76 to 81 near the shore to 62 to 68 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Mostly clear. Isolated showers in the evening. Lows 61 to 68 near the shore to 50 to 56 at 4000 feet. South winds up to 10 mph. Chance of rain 20 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 69 near the shore to 44 to 50 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows around 70 near the shore to 45 to 51 near 5000 feet. Light winds.

Waimea

Tonight: Partly cloudy. Isolated showers in the evening. Lows 60 to 68 near the shore to 52 to 59 near 3000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 77 near the shore to 67 to 76 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows 60 to 69 near the shore to 53 to 60 near 3000 feet. East winds up to 10 mph in the evening becoming light.

Kohala

Tonight: Partly cloudy. Isolated showers in the evening. Lows 60 to 68 near the shore to 52 to 59 near 3000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 77 near the shore to 67 to 76 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows 60 to 69 near the shore to 53 to 60 near 3000 feet. East winds up to 10 mph in the evening becoming light.

South Big Island

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 70 near the shore to around 49 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday: Sunny and breezy. Highs around 83 near the shore to around 66 near 5000 feet. East winds up to 20 mph.

Sunday Night: Mostly clear. Lows around 71 near the shore to around 50 near 5000 feet. East winds up to 10 mph.

Puna

Tonight: Partly cloudy with isolated showers. Lows 59 to 67 near the shore to 50 to 56 at 4000 feet. Light winds becoming west up to 10 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the morning. Highs 76 to 81 near the shore to 62 to 68 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Mostly clear. Isolated showers in the evening. Lows 61 to 68 near the shore to 50 to 56 at 4000 feet. South winds up to 10 mph. Chance of rain 20 percent.

Waikoloa

Tonight: Partly cloudy. Isolated showers in the evening. Lows 67 to 72 near the shore to around 50 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Highs 81 to 86 near the shore to 64 to 71 above 4000 feet. West winds up to 10 mph shifting to the northwest in the afternoon.

Sunday Night: Mostly clear. Lows 68 to 73 near the shore to around 51 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

Moderate trade winds will weaken tonight through the first half of next week. Conditions should remain fairly stable and dry, with low clouds and mainly isolated light showers favoring interior and mountain locations. Rain chances increase mid to late next week as a front moves slowly across the islands.

Discussion

A narrow band of high cirrus clouds is thinning out as it streams over the central portion of the island chain from west to east this afternoon. Some scattered low-level cloud development is noticeable on visible satellite imagery, mainly over the island interiors this afternoon, though little in the way of returns appear on radar. This indicates the moderate trades are already beginning to diminish, allowing sea breezes to form in the more wind-sheltered leeward areas today. The upper air balloon sounding from Hilo indicates a lowering subsidence inversion over the eastern end of the state, while Lihue's shows the inversion there eroding somewhat as a weak front approaches the offshore waters to the northwest. Generally stable conditions aloft will tend to limit cloud heights and keep the shower activity minimal, with very little in the way of rainfall for most areas through tonight.
The weak boundary approaching from the northwest will stall and dissipate northwest of the coastal waters through the remainder of the weekend. Otherwise, a weak subtropical ridge axis will remain over or near the islands with weak ridging aloft through the middle of next week. Winds will become light and variable over much of the state Sunday into Monday, then remain on the lighter side through Wednesday. During this time, expect clouds and showers to focus over the mountain and interior areas of each island due to sea breeze development during the late morning/early afternoon each day. Rainfall amounts will be light due to the large scale atmospheric stability.
By Thursday, long-range model guidance continues to show a shallow cold front creeping into the western islands from the northwest. While the GFS and ECMWF still differ on the speed of the front, increased showers and breezy trade winds will develop along the weakening boundary as it progresses eastward. All islands will likely benefit from a period of enhanced showers along the frontal band, especially along the windward mountain slopes. Both models have the front stalling out near Maui by Friday morning and breaking up/dissipating by the afternoon, with remnant unstable cloud bands drifting into each island on the strengthening easterly trade winds. The global models both indicate another front approaching the state from the northwest Saturday night into Sunday, uncertainty remains whether the boundary makes it to the islands before dissipating.

Aviation

Light to locally moderate trades will continue to weaken through the rest of the weekend, allowing for localized land/sea breeze development today that will become more widespread tomorrow. Isolated showers will favor mountain and interior areas of each island due to sea breeze development each afternoon, then clear out overnight with the land breezes. Brief MVFR conditions will be possible in showers, otherwise, VFR conditions will prevail.
AIRMET Tango is in effect for moderate turbulence between FL250 and FL450 across the state. SIGMET Papa for severe upper level turbulence is also in effect across the eastern half of the state. Upper level turbulence will likely taper off from west to east through the night into tomorrow morning as the subtropical jet pushes east of the area.

Marine

A cold front is currently stalled north of the coastal waters, resulting in light background winds across the area. This light background flow will shift to blow out of southeast on Sunday. Another front will approach from the northwest early next week will keep gentle south to southeast winds in place.
The extra-large northwest (310-320) swell that peaked well above guidance last night continues to slowly decline this afternoon. However, buoy observations from Hanalei and Waimea have been estimating the swell at about 10 feet, 15 seconds this afternoon. Based on buoy data and observations, although it has declined throughout the day, the swell appears to still be producing borderline warning-level surf along north and west facing shores. Therefore, the High Surf Warning that was previously in effect through this afternoon has now been extended through midnight tonight. The exception is for west facing shores of the Big Island, which has been downgraded to a High Surf Advisory (HSA) with this afternoon's forecast updates. As the swell continues to decline into this evening and tonight, surf should drop to advisory levels by early Sunday, and finally to sub-advisory levels by the end of the weekend. Additionally, a Small Craft Advisory (SCA) remains in effect for windward waters and all waters surrounding Kauai County for seas greater than 10 ft. Seas are expected to drop below 10 feet by early Sunday, at which point the SCA will be cancelled.
Looking ahead to next week, a stretch of elevated north and west shore surf is expected, produced by overlapping northwest pulses ranging from large to potentially extra-large, with the first arriving Tuesday and a larger one peaking Wednesday into Thursday. Surf along east facing shores will remain slightly elevated through the rest of the weekend due to the lingering short-period north-northeast swell. Early next week, surf along east facing shores will remain small. Surf along south facing shores will see an uptick heading into next week from a series of consecutive southwest pulses. This will result in small to moderate surf, peaking Monday and Tuesday.

Fire weather

Critical fire weather conditions are not expected through next week, as winds will remain well below the Red Flag Warning threshold through Thursday. Daytime relative humidity may briefly touch critical levels over the drier leeward areas into early next week, before increasing again with the arrival of a front and its associated showers moving through the state during the second half of the week.

HFO Watches/Warnings/Advisories

High Surf Warning until midnight HST tonight for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Koolau Windward, Molokai Windward, Molokai North, Molokai West, Windward Haleakala.
High Surf Advisory until 6 AM HST Sunday for Kona, Kohala.
Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov