Photo Credit: James Grenz

Hilo

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 88 near the shore to around 73 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 69 near the shore to around 54 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 82 to 88 near the shore to around 73 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 82 to 87 near the shore to around 70 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 72 to 77 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Today: Mostly sunny with isolated showers. Highs around 82 near the shore to 76 to 81 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to 57 to 62 near 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 82 near the shore to 76 to 81 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Today: Mostly sunny with isolated showers. Highs around 82 near the shore to 76 to 81 near 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to 57 to 62 near 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 82 near the shore to 76 to 81 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly sunny. Breezy. Highs around 86 near the shore to around 71 near 5000 feet. East winds up to 20 mph.

Tonight: Partly cloudy. Lows 68 to 74 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs around 86 near the shore to around 71 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 88 near the shore to around 73 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 69 near the shore to around 54 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 82 to 88 near the shore to around 73 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Today: Sunny in the morning then becoming partly sunny. Highs 83 to 88 near the shore to 70 to 76 above 4000 feet. Northeast winds up to 15 mph.

Tonight: Mostly clear. Lows 72 to 77 near the shore to 51 to 58 above 4000 feet. Light winds.

Saturday: Sunny in the morning then becoming partly sunny. Highs 83 to 88 near the shore to 70 to 76 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

Breezy trade winds will decrease through today, then remain at moderate strength through the weekend. Shower coverage will remain limited today, with the best rainfall chances over windward areas. An upper trough moving near the islands may trigger a modest increase in shower activity this weekend. Trades will increase early next week, with very gusty and dry conditions possible late Monday into Wednesday.

Discussion

Trades will weaken to moderate strength today as high pressure far north of the islands is nudged westward by a developing upper trough. However, upper ridging over the islands now will keep our airmass stable, and moisture within trade wind flow will remain slightly below normal. Expect windward rainfall to remain limited through today and, with the exception of a few afternoon showers over the Kona slopes of the Big Island, leeward areas will be dry.
Moderate trades will prevail this weekend as displaced high pressure holds far northwest of the islands. An upper trough will drop down toward the state on Saturday and stall near Kauai on Sunday. This will likely trigger an increase in shower activity, especially across the western end of the state. On Sunday night, the upper trough will weaken and be pushed away by strong upper ridging moving in from the east. This will lead to rebuilding trade winds and increased stability.
Expect windy and very gusty trade winds early next week, along with a period of stable and rather dry conditions. While it should continue to be monitored, guidance shows Dora passing south of the islands with deep high pressure moving in tandem to the north of Hawaii. Confidence is rising that we will experience a strong and rather dry trade wind flow with an unusually low inversion. This points toward limited showers with trade winds becoming strong and very gusty over and downwind of terrain. At the very least, a Wind Advisory will be needed for Tuesday and possibly as early as late Monday.

Aviation

A high pressure ridge north of the state will keep moderate trade winds in the forecast into Sunday. Brief passing showers are possible favoring the windward and mountain areas in the overnight to early morning hours. VFR conditions will prevail for most airfields into the weekend.
No AIRMETs in effect.

Marine

Easterly trades have lowered into the moderate to fresh range overnight due to a weakness that has formed in the ridge to the north. As a result, the Small Craft Advisory has been cancelled. A transition period is anticipated Sunday through early next week as the ridge strengthens to the north and Hurricane Dora enters the central Pacific on a westward track. This upward trend will continue Monday, then peak Tuesday into Wednesday as Dora passes well to the south. Wind speeds will reach the strong category for all waters through the day Monday, with gales expected over the windier channels and waters around Maui County and the Big Island late Monday through Tuesday. Seas will become rough and quickly exceed the Small Craft Advisory level over exposed waters beginning Monday into Monday night.
Surf along east facing shores will briefly ease into the weekend, then quickly ramp up and become rough late Sunday through early next week due to a combination of the aforementioned strong trades and large seas and a moderate long-period easterly swell generated from Dora. The largest surf is expected over the eastern end of the state, where heights could exceed the advisory level late Monday through Tuesday night. A downward trend is expected through the second half of the week as a more typical trade wind pattern returns and seas lower.
Surf along south facing shores will ease into the weekend with mainly a combo of background south and south-southwest swell energy rolling through. A short- to medium-period southeast swell is expected to fill in Tuesday through midweek as Dora passes far to the south. This will be a short-lived event with a peak occurring late Tuesday into early Wednesday.

Fire weather

The potential is rising for critical fire weather conditions early next week. Dry, stable, and breezy to locally windy trades are looking increasingly likely as deep high pressure to the north moves in tandem with Hurricane Dora, which is forecast to pass south of the islands. The Keetch Byram Drought Index (KBDI) is expected to reach the critical 600 mark by Tuesday, and models show leeward relative humidity may fall below 45 percent on Tuesday and Wednesday. We will also have to monitor conditions for Monday as drier conditions move in with building trades.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov