Hilo

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 73 near the shore to around 59 at 4000 feet. South winds up to 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then cloudy with occasional showers in the afternoon. Highs 81 to 88 near the shore to 67 to 72 at 4000 feet. East winds up to 10 mph. Chance of rain 80 percent.

Saturday Night: Mostly cloudy with occasional showers. Lows 67 to 74 near the shore to around 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

Kona

Tonight: Mostly clear. Isolated showers in the evening. Lows 73 to 78 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Saturday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 85 to 90 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 50 percent.

Saturday Night: Partly cloudy with isolated showers. Lows around 76 near the shore to 53 to 58 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 74 near the shore to 59 to 65 near 3000 feet. Light winds. Chance of rain 40 percent.

Saturday: Mostly sunny with scattered showers in the morning, then mostly cloudy with numerous showers in the afternoon. Highs 66 to 86. East winds up to 15 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows 67 to 74 near the shore to 60 to 67 near 3000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Kohala

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 74 near the shore to 59 to 65 near 3000 feet. Light winds. Chance of rain 40 percent.

Saturday: Mostly sunny with scattered showers in the morning, then mostly cloudy with numerous showers in the afternoon. Highs 66 to 86. East winds up to 15 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows 67 to 74 near the shore to 60 to 67 near 3000 feet. East winds up to 15 mph. Chance of rain 90 percent.

South Big Island

Tonight: Mostly clear. Lows around 75 near the shore to around 56 near 5000 feet. Northeast winds 10 to 15 mph.

Saturday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 88 near the shore to around 71 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Saturday Night: Breezy. Partly cloudy with isolated showers. Lows around 77 near the shore to around 57 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 73 near the shore to around 59 at 4000 feet. South winds up to 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then cloudy with occasional showers in the afternoon. Highs 81 to 88 near the shore to 67 to 72 at 4000 feet. East winds up to 10 mph. Chance of rain 80 percent.

Saturday Night: Mostly cloudy with occasional showers. Lows 67 to 74 near the shore to around 61 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

Waikoloa

Tonight: Partly cloudy with isolated showers. Lows around 77 near the shore to 54 to 59 above 4000 feet. Light winds. Chance of rain 20 percent.

Saturday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 85 to 91 near the shore to 68 to 75 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy with isolated showers. Lows around 78 near the shore to around 58 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The remnants of Tropical Cyclone Gilma will pass off to the northwest across the northern offshore waters of the state through Saturday morning. Deep tropical moisture in association with the low will aid in creating more efficient rainfall production while also maintaining this humid air mass. The cyclonic circulation across the far north offshore waters will continue to disrupt trade flow and produce gentle backing winds in time from east-to- west across the island chain through Saturday afternoon. The highest probabilities for periods of moderate to locally heavy rain will occur further west (Oahu and Kauai) through Saturday afternoon. The threat for locally heavy rain will also persist into Saturday afternoon as convective bands rotating around the backside of this fairly progressive northwest-heading remnant low impact more leeward- facing areas of the islands. Moisture from the remnants of once Tropical Storm Hector passing across the state will keep statewide rain chances for showers moderate to high Saturday night and Sunday morning.

Discussion

Mid afternoon visible satellite depicts the remnant low of what was once TC Gilma passing approximately 100 miles north northwest of Kahului on the island of Maui. The best rainfall production with this system has generally remained along its northern flank There have been periods of afternoon moderate to locally heavier rain (Ewa side of Oahu, Kohala region on Big Island) within the low's southern rain bands. Recent soundings show a continued deep, moist boundary layer with no trade wind inversion. Above normal (75% to near 90% percentile) pwats are evidence of a very moist air mass. The lack of trades and this higher-than-normal moisture (surface dew points in the lower to middle 70s) have introduced a taste of the mainland Muggy South across the Aloha State.
The majority of the rain associated with the remnants of Gilma has fallen offshore but many more windward locations on Big Island and Maui County have picked up about a half an inch to slightly over an inch and half of rain the past 12 hours (the winning rain gauge was Maui's West Wailuaiki at 2.18 inches). As the low moves further west, southern bands of rain will stream across the state. Rainfall within these southern bands may quickly put down a quick half an inch to inch over climatological direr leeward areas through tomorrow. This beneficial rain will alleviate some of southern and western Maui's drought conditions the next couple of days. The progressive northwestern movement of the low north of Oahu and Kauai through tomorrow should keep these convective bands transitioning west but there may be some slower-moving streamer bands that could produce greater than 2 inches of short term rain accumulation(s). While chances remain low of thunder, a near zero probability does exist of the occurrence of early evening thunderstorms. Orographic lift within this unstable and very moist profile within the presence of the low may be enough to allow very isolated towering cumulus to reach their full potential (in a warmed upper 70/lower 80 F air mass).
The movement of the remnant low will keep light and variable winds in the forecast through tomorrow. Regional land and sea breezes will likely rule through most of the day Saturday before the gradient back to the subtropical high is restored and trades return Sunday. Afternoon sea breezes will build clouds over more mountainous interior sections. Brief leeward showers are possible as light background winds converge with sea breezes. A weak disturbance associated with the remnants of TS Hector will approach the islands this weekend. This disturbance may produce another round of showers overnight Saturday night into Sunday morning.
High pressure far north of the state will allow trades to strengthen back to breezy magnitudes by late Sunday or after the remnants of Hector pass across the islands. More stable conditions will also return to the area next week as better established high pressure far north of the state expands more east and southeast. Next week's trades will reinstate traditional trade wind weather. That being of diurnal showers that will typically stick to windward-exposed slopes and elevated terrain primarily during the overnight hours.

Aviation

As remnants of former Tropical Cyclone Gilma pass just north of Oahu tonight, periods of showery weather and MVFR ceilings are possible especially over the western half of the state through Saturday morning. Weather conditions should generally improve over the eastern half of the state this evening and tonight, but some scattered showers may linger around Maui County. Brief IFR conditions are possible with the heavier showers (most likely around Oahu or Kauai tonight).
AIRMET Sierra for mtn obsc is in effect for windward portions of Maui, Molokai and Oahu due to low ceilings and showers. AIRMET Sierra may expand to Kauai tonight as showers increase over Kauai.

Marine

Remnants of Gilma, just outside the coastal waters about 90 nautical miles northeast of Honolulu is forecast to pass just north of the islands through tonight. Trade winds will decline to gentle to moderate strength, then switch out of the southeast to south after the circulation passes by. Heavy showers and isolated thunderstorms may develop near Gilma as it moves through. Southeasterly winds will slowly build and become more easterly on Saturday, followed by moderate to locally strong easterly trade winds Sunday through at least the middle of next week.
Surf along east facing shores will continue to diminish today. Returning trade winds will produce moderate east shore surf Sunday into early next week.
Generally small surf will prevail on other shores. Small background swells from the south and southeast will keep the surf from going entirely flat for south facing shores. Small northwest swell is expected to slowly diminish during the weekend returning to typical summertime flat conditions.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov