Hilo

Tonight: Mostly cloudy with numerous showers. Lows 66 to 71 near the shore to around 56 at 4000 feet. Northeast winds up to 10 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 82 to 87 near the shore to around 71 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 71 near the shore to around 57 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Kona

Tonight: Partly cloudy with isolated showers. Lows around 74 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Sunny. Isolated showers in the afternoon. Highs 84 to 89 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday Night: Mostly clear with isolated showers. Lows 72 to 77 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 near the shore to 58 to 63 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82 near the shore to 72 to 79 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows 66 to 71 near the shore to 59 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 near the shore to 58 to 63 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82 near the shore to 72 to 79 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows 66 to 71 near the shore to 59 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly clear. Isolated showers in the evening. Lows around 72 near the shore to around 54 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Isolated showers in the afternoon. Highs around 87 near the shore to around 72 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Breezy. Lows around 73 near the shore to around 54 near 5000 feet. Northeast winds up to 20 mph.

Puna

Tonight: Mostly cloudy with numerous showers. Lows 66 to 71 near the shore to around 56 at 4000 feet. Northeast winds up to 10 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 82 to 87 near the shore to around 71 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 71 near the shore to around 57 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly clear. Lows around 74 near the shore to 53 to 58 above 4000 feet. East winds up to 10 mph. Gusts up to 30 mph.

Friday: Sunny and breezy. Highs around 88 near the shore to 70 to 76 above 4000 feet. Northeast winds up to 20 mph.

Friday Night: Mostly clear. Lows around 75 near the shore to 53 to 58 above 4000 feet. Northeast winds up to 15 mph shifting to the southeast after midnight. Gusts up to 35 mph.

Detailed Forecast

Synopsis

Gentle to low end breezy trade winds will occur through the remainder of the day. Trades will strengthen to more areawide breezy magnitudes Friday through most of next week. Showers will typically favor windward and mauka locations, particularly during the overnight into early morning hours.

Discussion

The remnant of what was once T.C. Emilia in the eastern Pacific is moving across the local western waters as a broad open wave trough. Subtle mid level cooling brought on by a lingering upper level trough, its axis orientated from the islands off to the northeast, along with higher 850-700 mb layer moisture will keep higher-end windward/higher elevation rain probabilities in place through late Friday night. Offshore showers will primarily stick and dump the highest rain amounts over better east to northeastern exposed windward and mauka locations. Heat of the day interior (leeward) thicker clouds and increased shower activity (i.e., Big Island Kona regions) cannot be ruled out where localized afternoon sea breeze boundaries set up.
Breezy trade winds are expected to return Friday and persist through next week as the weak open wave trough mentioned above travels west away from the state and the subtropical high northeast of the islands fills in and regains better control. After a relatively drier Saturday, general weak mid-upper level ridging, with periodic ribbons of passing higher moisture, may result in increasing shower coverage to begin next week. Confidence is still shaky on the development of a tropical depression or cyclone southeast of the islands next week. If a system does development and move across those waters south of Big Island next Thursday or Friday, the upcoming late week forecasts will trend more wet for the eastern end of the state.

Aviation

Moderate to locally breezy trades will deliver low cigs and SHRA to windward and mauka areas through the forecast period. MVFR conds can be expected in any SHRA but VFR should prevail.
No AIRMETs are currently in effect. AIRMET Sierra may be needed for mtn obsc for windward locations particularly overnight and in the early morning hours with increased SHRA.

Marine

A weak surface trough passing by north of the islands will keep the trade winds at moderate to locally fresh speeds through this evening. As the trough exits the area, the trades will begin strengthening tonight. The trades should strengthen back to locally strong speeds late tonight, then hold at these levels through early next week. A Small Craft Advisory (SCA) is in effect starting midnight tonight for the typical windy waters around Maui County and the Big Island.
The current small south swell should hold through tonight then gradually decline the next few days. Small background energy from the southeast is also possible during the next few days. A more significant south swell will arrive late Sunday and Sunday night, peak above the summertime average Monday, then slowly lower through the middle of next week.
Seasonally flat to tiny surf is expected through early next week for north facing shores. East shore surf will remain below normal during the next couple days, then trend higher over the weekend and rise to near seasonal levels early next week.
The combination of the full moon and water levels running around 0.5 ft higher than normal should produce minor coastal flooding each afternoon along the shorelines across the state beginning 8/18 and likely continuing through 8/20. A Coastal Flood Statement will eventually be needed as we get closer to the event.

HFO Watches/Warnings/Advisories

Small Craft Advisory from midnight tonight to 6 AM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov