Hilo

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 86 near the shore to 64 to 73 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 70 near the shore to 53 to 58 at 4000 feet. Light winds. Chance of rain 50 percent.

Monday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 80 to 85 near the shore to 65 to 73 at 4000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Kona

Today: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 82 to 89 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 71 near the shore to 50 to 55 near 5000 feet. Light winds. Chance of rain 40 percent.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 82 to 88 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Mostly sunny in the morning then becoming mostly cloudy. Isolated showers. Highs 67 to 88. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 61 to 68 near the shore to 53 to 61 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 68 to 88. Light winds. Chance of rain 20 percent.

Kohala

Today: Mostly sunny in the morning then becoming mostly cloudy. Isolated showers. Highs 67 to 88. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 61 to 68 near the shore to 53 to 61 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 68 to 88. Light winds. Chance of rain 20 percent.

South Big Island

Today: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 85 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 71 near the shore to around 51 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 83 to 88 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 20 percent.

Puna

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 86 near the shore to 64 to 73 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 70 near the shore to 53 to 58 at 4000 feet. Light winds. Chance of rain 50 percent.

Monday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 80 to 85 near the shore to 65 to 73 at 4000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Waikoloa

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 81 to 89 near the shore to 67 to 74 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 71 near the shore to 48 to 56 above 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 81 to 89 near the shore to 67 to 74 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A cold front passing far north of the islands will weaken the high pressure ridge north of the state through the week. Moderate trade winds will weaken over the next two days with strengthening afternoon sea breezes over the islands. The ridge will build back in north of the region on Thursday with increasing trade winds into the moderate to locally breezy range from Friday into next weekend. Clouds and brief passing showers will shift back to windward and mountain areas favoring the overnight to early morning hours in this trade wind weather regime.

Discussion

A stability signature remains in the water vapor satellite imagery. However, low level convergence is strong enough to lift the subsidence inversion to around 8,000 to 9,000 feet as shown in the 2 AM HST upper air balloon launches from Lihue and Hilo this morning. Deep enough to produce scattered to numerous showers mainly over windward areas shown on local radar imagery. Rainfall amounts vary between 0.01 to 0.25 inches overnight based on surface observations at windward locations. Diurnal trends will decrease shower activity across the state through the morning hours.
A cold front passing far north of the islands will weaken the high pressure ridge north of the state this week. Moderate trade winds will weaken over the next two days with strengthening afternoon sea breezes over the islands. Clouds and a few showers will shift to mountain and island interior sections each afternoon in this sea breeze weather pattern. Model cross sections show subsidence temperature inversion heights in the 5,000 to 7,000 foot range into Wednesday. Forecast guidance suggests a low level convergence boundary will drift in from the north late Wednesday into Thursday as trade winds start to return, boosting inversion heights into the 7,000 to 9,000 foot range, allowing deeper clouds to form and producing slight increases in dry season shower activity.
The ridge will build back in north of the region on Thursday with increasing trade winds into the moderate to locally breezy range into next weekend. Clouds and brief passing showers will shift back to windward and mountain areas favoring the overnight to early morning hours in this trade wind weather regime.
In the extended range forecast there is a bit of hope for some enhanced shower activity. The long range models are suggesting a low level trough passing through the islands from next week Friday to Saturday. If this trough passes through the islands as shown by the long range model guidance then expect a slight upward trend in shower activity by next week Saturday for at least the Big Island and windward Maui County.

Aviation

Breezy easterly trades early today, will weaken tonight into Monday. This trade wind pattern will maintain showers across favored windward and mauka areas. Drier air streaming across the state will limit moisture, generating mainly VFR conditions through the TAF period. Brief MVFR cigs will drift across windward areas through this morning, though are not expected to be widespread and remaining below AIRMET criteria.
Low-level turbulence downwind of the terrain, remains possible across some locations into this afternoon.

Marine

Fresh easterly trades will continue to ease through Monday in response to a weakness in the ridge forming due to a front dropping southward from the eastern Aleutians. Light to moderate easterly background flow with localized land and sea breezes are anticipated late Monday through Wednesday. A return of fresh easterly trades is expected late Wednesday into the second half of the week.
After a nice run through the second and third week of August for south swells moving through, a quiet spell has set in that will linger into the first week of September for surf along southern exposures. Models reflect this and show the pattern over the southern hemisphere within Hawaii's swell window has transitioned to a more zonal and progressive setup (not a good setup for swell generation here in the islands). Expect a combo of small background southeast and southerly energy moving through – likely enough to keep the surf from going flat this week.
Similar surf is expected along north facing shores for the week as the northern Pacific remains quiet. Guidance does show a batch of fresh to strong northerly breezes expanding southward behind the aforementioned front today through Monday between the Date Line and the Gulf of Alaska that may support a northerly pulse later in the week (hardly noticeable at most exposures). Compact low pressure system spinning up along this front in the Gulf of Alaska around midweek could generate a small north- northeast pulse for next weekend, but that is about it as we head into September.
Surf along east facing shores will remain small and choppy with the fresh easterly trades holding today, then ease through the first half of the week as the trades diminish.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov