Hilo

Today: Mostly sunny with scattered showers in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 86 near the shore to 70 to 75 at 4000 feet. North winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 70 near the shore to around 56 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny with scattered showers in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 86 near the shore to 70 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Kona

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 71 to 76 near the shore to around 57 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 84 near the shore to 70 to 81 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 70 near the shore to 58 to 64 near 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 30 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 84 near the shore to 70 to 81 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 84 near the shore to 70 to 81 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 70 near the shore to 58 to 64 near 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 30 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 84 near the shore to 70 to 81 near 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

South Big Island

Today: Mostly sunny. Breezy. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 20 mph.

Tonight: Mostly clear. Lows around 72 near the shore to around 55 near 5000 feet. East winds up to 15 mph.

Friday: Sunny in the morning then becoming partly sunny. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 15 mph.

Puna

Today: Mostly sunny with scattered showers in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 86 near the shore to 70 to 75 at 4000 feet. North winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 70 near the shore to around 56 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny with scattered showers in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 86 near the shore to 70 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Waikoloa

Today: Mostly sunny. Breezy. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 20 mph.

Tonight: Mostly clear. Breezy. Lows around 74 near the shore to 53 to 60 above 4000 feet. East winds up to 20 mph.

Friday: Sunny in the morning then becoming partly sunny. Breezy. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 20 mph.

Detailed Forecast

Synopsis

Shower activity will trend lower for all islands as more stable and drier air moves into the region through Friday. Wind speeds will decrease to moderate levels from Friday through the weekend as the ridge far north of the state weakens. Deeper tropical moisture, associated with remnants of former tropical cyclone Fernanda, will rise from east to west starting on Sunday. Humidity levels and rainfall activity will increase for all islands through Tuesday night, favoring Maui and the Big Island. A transition back to more typical trade wind weather starts next week Wednesday.

Discussion

Starting with the water vapor satellite imagery this morning we see a similar pattern from last night, showing a narrow upper level trough, the TUTT, with two embedded upper lows just northwest of the islands. This upper trough will drift eastward today and help to weaken Tropical Storm Greg as it continues to track westward, remaining far south of the Hawaiian Islands. Subsidence to the north of Greg will produce stable and fairly dry conditions over the region through Friday. Upper air balloon soundings from Lihue and Hilo at 2 AM HST this morning show the trade wind temperature inversion height already dropping to the 5,000 foot level.
The high pressure ridge far north of Hawaii will keep moderate to locally breezy trade winds in the forecast through tonight. The ridge will weaken north of the state on Friday, slightly decreasing trade wind speeds through the weekend. Trade winds will restrengthen into the moderate to breezy range by Tuesday as the remnants of Fernanda pass to the south of the state.
A small scale ridge forming just north of Greg will produce a slight drying trend over the islands through Friday as trade wind temperature inversion heights remain around 5,000 feet elevation. Low cloud cover and shower activity will decrease across the region due to the low temperature inversion heights capping vertical cloud development. These stable dry trends will begin to ease up on Saturday with a return to brief passing showers over windward areas in the overnight to early morning hours.
Deeper tropical moisture, associated with the remnants of former tropical cyclone Fernanda will move into the eastern islands starting on Sunday, and spread westward across the state on Monday and Tuesday. Global model guidance showing the deepest moisture with this remnant trough will remain south of the island chain. However, we continue to see enhanced rainfall activity increasing across most islands as the trough moves westward through the region. Locally heavy rain is possible with this pattern along with isolated thunderstorms. The highest rainfall amounts are forecast to fall from Monday afternoon through Tuesday morning along windward and mountain slopes, favoring Maui and the Big Island. A transition back to more typical trade wind weather starts next week Wednesday.

Aviation

Surface high pressure northeast of the state will allow for moderate to locally breezy conditions to persist through the remainder of the forecast period. Isolated to scattered showers will affect mainly windward areas this morning. Drier air is forecast to filter in from the east later today and lead to a decrease in overall shower coverage.
No AIRMETs are currently in effect.

Marine

The presence of Tropical Storm Greg south of the Hawaiian Islands is maintaining moderate to strong trades through tonight. As a result, Small Craft Advisory remains in effect for the typical windy waters around Maui and the Big Island through tonight. Winds then weaken to moderate levels Friday through Sunday as Greg weakens and continues its trek westward. Trades become locally strong once again early next week as the remnants of Tropical Storm Fernanda approach the islands from the east.
A series of small reinforcing northwest swells will keep north shore surf up above typical summertime flat levels through the remainder of the work week. North and west shore surf will return to flat levels Saturday through early next week. South shore surf will remain small and below the summertime average through the weekend, with mainly background southerly swells. A small south swell may boost south shore surf up close to the summertime average early next week.
East shore surf will remain below normal levels through the weekend due to lack of strong trades upstream of the island chain. Long period east swell generated from Tropical Storm Hillary off Baja California could impact east facing shores during the middle of next week but still dependent on the size and intensity of the storm.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 4 AM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov