Photo Credit: Randy Alona Gallegos

West Side

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 80 to 91. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows 67 to 74. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs 79 to 91. Northeast winds up to 10 mph shifting to the west around 10 mph in the afternoon. Chance of rain 40 percent.

South Side

Today: Sunny and breezy. Highs around 90. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon.

Tonight: Mostly clear. Lows 66 to 74. Light winds.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 90. North winds up to 10 mph shifting to the northwest around 10 mph in the afternoon. Chance of rain 20 percent.

North Shore

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 89 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 70 near the shore to 47 to 53 near 5000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 89 near the shore to around 68 near 5000 feet. Southeast winds up to 10 mph shifting to the northeast around 10 mph in the afternoon. Chance of rain 40 percent.

Central Maui

Today: Breezy. Mostly sunny with isolated showers. Highs 84 to 91. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 72. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 84 to 92. Northeast winds up to 10 mph. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 62 at the visitor center to around 56 at the summit. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows around 46 at the visitor center to around 42 at the summit. East winds up to 10 mph shifting to the north after midnight. Chance of rain 50 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 63 at the visitor center to around 58 at the summit. North winds around 10 mph shifting to the south in the afternoon. Chance of rain 40 percent.

East Maui

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 89 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 70 near the shore to 47 to 53 near 5000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Monday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 89 near the shore to around 68 near 5000 feet. Southeast winds up to 10 mph shifting to the northeast around 10 mph in the afternoon. Chance of rain 40 percent.

Lanai City

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 75 to 83. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 62 to 67. Northeast winds up to 10 mph in the evening becoming light.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 75 to 83. Light winds. Chance of rain 20 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 71 to 91. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 57 to 73. East winds around 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 71 to 92. Southeast winds around 10 mph in the morning becoming light. 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