Hilo

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then scattered showers after midnight. Haze through the night. Locally heavy rainfall possible in the evening. Lows 59 to 66 near the shore to 48 to 55 at 4000 feet. Light winds. Chance of rain 70 percent.

Saturday: Haze in the morning. Partly sunny with scattered showers. Highs 76 to 81 near the shore to 62 to 68 at 4000 feet. West winds up to 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 60 to 67 near the shore to 47 to 55 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain 70 percent.

Kona

Tonight: Partly cloudy with isolated showers. Lows around 70 near the shore to 43 to 50 near 5000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny. Isolated light showers in the morning, then scattered showers in the afternoon. Highs around 83 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Saturday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 70 near the shore to 43 to 49 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the evening, then scattered showers after midnight. Haze after midnight. Lows 59 to 68 near the shore to 52 to 60 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs around 77 near the shore to 68 to 76 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 59 to 69 near the shore to 51 to 59 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the evening, then scattered showers after midnight. Haze after midnight. Lows 59 to 68 near the shore to 52 to 60 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs around 77 near the shore to 68 to 76 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 59 to 69 near the shore to 51 to 59 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated light showers after midnight. Haze after midnight. Lows around 71 near the shore to around 50 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Saturday: Mostly sunny. Breezy. Isolated light showers in the morning, then scattered showers in the afternoon. Highs around 83 near the shore to around 66 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Saturday Night: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 71 near the shore to around 50 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 30 percent.

Puna

Tonight: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the evening, then scattered showers after midnight. Haze through the night. Locally heavy rainfall possible in the evening. Lows 59 to 66 near the shore to 48 to 55 at 4000 feet. Light winds. Chance of rain 70 percent.

Saturday: Haze in the morning. Partly sunny with scattered showers. Highs 76 to 81 near the shore to 62 to 68 at 4000 feet. West winds up to 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 60 to 67 near the shore to 47 to 55 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain 70 percent.

Waikoloa

Tonight: Partly cloudy with isolated light showers. Lows around 70 near the shore to 46 to 52 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated light showers. Highs 81 to 86 near the shore to 64 to 70 above 4000 feet. East winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Saturday Night: Partly cloudy with isolated showers. Lows around 70 near the shore to 47 to 52 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Dry and stable conditions will persist through the remainder of the afternoon and into the evening hours. There will be a subtle change to a warmer, slightly more wet pattern this weekend. Gentle statewide winds will veer around to the northeast by tonight and this trade wind behavior will anchor in place through the middle of next week. Higher plumes of moisture brought in on the trades will enhance mainly windward area and mauka slope showers, with infrequent short-lived leeward shower activity, through Monday.

Discussion

A comfortably dry day under partly cloudy skies and gentle northerlies. This morning's dewpoint temperatures lower 50s to around 60 F within a very dry dawn air mass, along with mainly clear skies and light breezes, allowed many communities to fall into the lower to middle 60s or about 10 degrees below season norms. This has been a transition day as dewpoints have slowly recovered into the average lower elevation lower to mid 60s. There will be a gradual moisture modification of the resident air mass through Sunday as gentle veering winds to the northeast and east tap into a more moist air mass east of the state. The current synoptic set up also leans toward a more wet weekend. A upper low nearly a thousand miles north of the islands will be absorbed by a large trough racing across the northern Pacific. This will deepen the trough and enhance the northern advection of lower latitude moisture over the eastern half of the state. This will promote higher mid layer moisture to rotate in from the south southeast along the backside of mid level ridging centered far northeast of the state. This scenario will be the impetus to increasing shower coverage across both Big Island and Maui the next couple of days. Thicker clouds and the highest rain totals will focus along windward exposures and higher elevations, with the main focus being along east Maui and Big Island as this slug of higher mid- lower layer moisture advances west and across the island chain. Emissions from the recent Kilauea eruption in the Halema'uma'u crater this past Wednesday are modeled to be light enough, with strengthening (mixing) trades, to keep the highest SO2 closer the surface with the vog mainly impacting areas of interior Big Island through Saturday.
The timing and the depth of the aforementioned passing upper trough early next week will determine how close thunderstorms form to Big Island. There is a chance of there being just enough upper level support, with the arrival of deeper lower level moisture tonight, to mention a very small chance of thunder developing just offshore of the Hilo regions this evening through early Saturday. Numerical weather prediction (NWP) guidance does hint at a very slight chance (10% NBM probs) with the GFS deterministic depicting a moderately unstable environment and lower Showalter Indices over Big Island and points northeastward. Weak ridging will control the early week weather pattern and support typical trade wind shower behavior. A weak front approaching from the north will pass just north of the state Monday. This boundary will aid in sticking moisture over the state and keeping a more wet trade pattern in place into Tuesday. Extended forecast guidance is consistent in holding onto the idea of slow developing mid to upper troughing and a northwest flow pattern that will favor lower pressures evolving west and south of Hawaii. While there are still considerable differences in NWP model guidance, a cut-off low will develop around mid week northwest of the state. A fair number of ensemble members are also latching onto a passing low/open wave trough dynamically passing to the north of the island chain late next week. The impacts of this low's (or trough's) potential development and evolution will be unknown until the event begins to unfold mid next week. Thus, it is best to keep any speculation about Day 6 and 7's weather pattern change at bay until later this weekend when NWP probabilities have a better handle on the dynamics.

Aviation

Strengthening trade winds will deliver increasing amounts of low clouds and showers to windward areas. Showers will be in greatest coverage/intensity over windward portions of Maui and the Big Island, where some heavy showers and/or thunderstorms are possible tonight, producing tempo MVFR VIS/CIG and the potential for isol IFR conditions. AIRMET Sierra is posted for moutain obscuration on the Big Island.

Marine

Ridging will lift north away from the region through the weekend. Prevailing winds will be to light to moderate trades this evening, becoming moderate to fresh this weekend as the ridging lifts northward. By early next week, a trough will move into the region from the east as a cold front approaches from the northwest.
Latest buoy and surf observations show that borderline High Surf Advisory-level surf remains in place across north facing shores of the smaller islands. Therefore, the High Surf Advisory has been extended through 6 am HST Saturday. However, the mix of north and northwest swell energy is expected to continue declining overnight, and surf should fall below advisory levels by dawn. Buoys also show that significant wave heights have fallen below 10 feet this afternoon, so the Small Craft Advisory has been cancelled.
Another series of overlapping, moderate sized north and northwest swells will move through the islands during the first half of next week, giving a boost to north shore surf (though it is expected to be smaller than this most recent swell). Meanwhile, east shore surf should remain below normal through the middle of next week. South shore surf will also remain at very small levels throughout the next several days.

Fire weather

Afternoon RH values are in the 40s again today, but winds will fall short of the critical fire behavior threshold. Minimum RH values will then rebound above 45 percent Saturday into early next week. Thus, no critical fire behavior is expected during the forecast period.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Saturday for Niihau, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala.

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Data Courtesy of NOAA.gov