Hilo

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 50 to 56 at 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to around 65 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 59 to 68 near the shore to 49 to 56 at 4000 feet. Northeast winds up to 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Haze. Lows around 71 near the shore to 47 to 52 near 5000 feet. Light winds.

Saturday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 82 to 87 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 20 percent.

Saturday Night: Mostly clear with isolated showers. Lows 68 to 73 near the shore to 45 to 52 near 5000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 61 to 70 near the shore to 53 to 61 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday: Mostly sunny. Breezy. Highs 64 to 83. East winds up to 20 mph.

Saturday Night: Partly cloudy with isolated showers. Lows 60 to 69 near the shore to 52 to 60 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 61 to 70 near the shore to 53 to 61 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday: Mostly sunny. Breezy. Highs 64 to 83. East winds up to 20 mph.

Saturday Night: Partly cloudy with isolated showers. Lows 60 to 69 near the shore to 52 to 60 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Windy. Mostly cloudy with isolated showers. Haze. Lows around 73 near the shore to around 53 near 5000 feet. East winds 10 to 30 mph decreasing to up to 30 mph after midnight. Chance of rain 20 percent.

Saturday: Breezy. Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to around 65 near 5000 feet. East winds up to 25 mph. Chance of rain 30 percent.

Saturday Night: Mostly clear. Breezy. Lows around 72 near the shore to around 52 near 5000 feet. Northeast winds up to 25 mph.

Puna

Tonight: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 50 to 56 at 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to around 65 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 59 to 68 near the shore to 49 to 56 at 4000 feet. Northeast winds up to 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 72 near the shore to 49 to 54 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny. Highs 82 to 87 near the shore to 64 to 71 above 4000 feet. Northeast winds up to 15 mph shifting to the northwest in the afternoon.

Saturday Night: Mostly clear. Lows 68 to 73 near the shore to 47 to 53 above 4000 feet. North winds up to 15 mph shifting to the east after midnight.

Detailed Forecast

Synopsis

Moderate trades deliver limited clouds and showers windward and mauka into next week.

Discussion

ESE flow in the low and mid-levels is supplying adequate moisture for frequent showers over favored slopes of Windward Big Island and Maui this afternoon where 24 hour rainfall totals have ranged from a couple tenths to around 1.5″. Meanwhile terrain-parallel flow has allowed persistent showers to develop over the Ko'olau range on Oahu while the sea breeze has also capitalized on resident moisture allowing showers to develop over and leeward of the Waianae Range. All shower activity will begin diminishing this evening, the latter with the loss of diurnal heating and the former as winds back to easterly and usher moisture west of the islands.
A much drier airmass lurks immediately upstream of the island as evidenced by recent water vapor imagery and a limited coverage of low clouds on visible. This airmass will pivot into the area tonight into Saturday bringing considerably drier conditions as sea level dewpoints fall from the mid to upper 60s into the low 60s by evening. Moderate trades during this time will be accompanied by limited light showers mostly sunny skies with the exception of the Big Island where clouds and a few light showers will favor upslope areas Saturday afternoon. Highly stable, moderate trades then continue into the middle of next week with very limited rainfall windward and mauka.
Extended guidance teases a more active or at least more interesting pattern developing during the second half of next week beginning with surface winds veering to southerly by Thursday in response to a frontal wave developing northwest of the islands. Initially benign other than an increase in dewpoints, the attendant cold front sweeps into the forecast area late in the period bringing a round of showers and falling dewpoints. Though differences abound at the surface, synoptically the global models point toward blocking high pressure establishing over the western Aleutian Islands with a tendency for low pressure to establish near/upstream of the islands heading into mid December.

Aviation

Moderate to locally breezy east-southeasterly winds will gradually weaken through Saturday as the surface high to the far northeast weakens and drifts further eastward. With the slightly veered flow, showers will continue to stream into south and east facing slopes of all islands and convergent boundaries downwind of island terrain will provide a source of isolated to scattered showers to leeward areas of some of the smaller islands through this evening. MVFR, or even brief IFR conditions will be possible in these showers. Drier air will move in overnight allowing for limited shower activity focused over windward and mountain areas tonight through Saturday, with VFR conditions generally prevailing.
AIRMET Sierra for mountain obscuration is in effect for all of Oahu and east and south facing slopes of the Big Island.
AIRMET Tango is in effect for moderate low level turbulence over and downwind of island terrain.
Both of these AIRMETs will likely be able to be cancelled this evening.

Marine

A surface trough west of Kauai will continue to gradually weaken and retrograde westward away from the islands tonight into the weekend. Meanwhile, surface high pressure is building northeast of the state. This will allow moderate to locally strong east to east-southeast winds to persist into Saturday. A Small Craft Advisory (SCA) remains in effect through tonight for most Hawaiian coastal waters due to a combination of winds and seas of 10 ft or greater. By Saturday morning, however, seas are expected to decline below SCA levels as northwest swell energy fades. Therefore, the SCA will be reduced to the typically windy waters of Maui County and the Big Island for the day on Saturday. Moderate trades will continue through the first half of the week, followed by lighter east-southeast flow during the second half of the week.
A moderate, medium period northwest swell that was on a slight decline earlier today has been followed by a slightly longer period northwest reinforcement this afternoon. This has resulted in an uptick in surf along north and west facing shores during the day today. Based on observations from both the Waimea buoy and offshore buoy 51001, the High Surf Advisory (HSA) for north and west facing shores has been extended through 6AM HST Saturday morning, and surf heights have been updated accordingly. This northwest swell energy will gradually fade this weekend, bringing surf back down below average Sunday and Monday. Another northwest swell arriving late Tuesday or Tuesday night could bring surf back up to near or slightly above advisory levels again for the middle part of the week for north and west facing shores.
Choppy east shore surf will remain small and decline this weekend as trades ease. Expect minimal background energy for south facing shores through the next few days, other than a slight bump this weekend.
Peak monthly tides combined with water levels that are running higher than predicted will likely lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is possible around the daily peak tide, which will be during the early morning hours. This could also magnify effects of the high surf on coastal areas along north and west facing shores around the same time frame.

Fire weather

The inversion slopes from around 8kft at Lihue to 11kft at Hilo. Drier air filters into the area for Saturday but moderate trades unlikely to reach the critical fire threshold. Dry weather and relatively light winds continue well into next week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov