West Side

Today: Sunny. Highs around 84. East winds up to 15 mph.

Tonight: Partly cloudy with isolated showers. Lows 68 to 75. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs around 84. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

South Side

Today: Sunny and breezy. Highs around 89. Northwest winds up to 20 mph.

Tonight: Mostly clear. Lows 69 to 76. Northwest winds up to 15 mph.

Monday: Sunny. Highs around 89. Northwest winds up to 15 mph.

North Shore

Today: Breezy. Mostly sunny with isolated showers. Highs 80 to 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72 near the shore to around 52 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 80 to 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Central Maui

Today: Sunny and breezy. Highs 83 to 90. East winds up to 20 mph.

Tonight: Mostly clear. Isolated showers after midnight. Lows around 70. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Sunny and breezy. Isolated showers in the morning. Highs 83 to 90. East winds up to 20 mph. Chance of rain 20 percent.

Upcountry

Today: Sunny with isolated showers. Highs around 66 at the visitor center to around 72 at the summit. Southeast winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 44 to 55. East winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs around 66 at the visitor center to around 72 at the summit. East winds up to 10 mph. Chance of rain 20 percent.

East Maui

Today: Breezy. Mostly sunny with isolated showers. Highs 80 to 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72 near the shore to around 52 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 80 to 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Lanai City

Today: Sunny. Highs 74 to 82. Light winds becoming southeast up to 10 mph in the afternoon.

Tonight: Mostly clear. Lows 64 to 69. Northeast winds up to 10 mph in the evening becoming light.

Monday: Sunny. Highs 75 to 83. Light winds becoming north up to 10 mph in the afternoon.

Kaunakakai

Today: Sunny. Highs 75 to 90. East winds 10 to 15 mph.

Tonight: Mostly clear. Lows 60 to 74. East winds up to 15 mph.

Monday: Sunny. Highs 75 to 90. East winds up to 10 mph increasing to 10 to 15 mph in the afternoon.

Detailed Forecast

Synopsis

Hawaii will remain under the influence of high pressure ridging to the north and east as a trough lingers north of the state. This will result in light to locally breezy trade winds today. There will be a slight drop off in wind speeds tomorrow in response to the trough sagging south and weakening the downstream pressure gradient. Generally a dry, stable and very warm summer weather pattern will prevail with only occasional light windward mauka trade showers. The lone exception will be scattered afternoon and evening showers over the Kona slopes of Big Island the next couple of days.

Discussion

Mid to upper level ridging centered north and east of the islands will be the main control to persistent warm and dry conditions. A 500 mb 589 dam high pressure ridge, with the 1023 mb surface high centered 1,200 miles from Hilo, is resulting in a stable late August dry trade wind weather. Early morning satellite trends verify these stable conditions with widely-scattered warm low topped clouds moving in on generally moderate to fresh easterly trade flow. 12Z local soundings depict a strong 5-7k ft trade inversion height and below normal near one inch precipitable waters (pwats) in Hilo (falling into the lower quartile for this time of year). A higher ribbon of moisture expanding up from the south-southwest into the far western end of the state this morning has Lihue at near normal 1.41 inch pwats. A northern trough axis will settle south and weaken the pressure gradient over the region enough to allow trades to fall back to more light to moderate speeds the next couple of days. Rainfall has been nearly non- existent across most windward areas and, other than a few showers developing along the Kona slopes of Big Island and within the smaller island windward mauka regions, leeward areas will remain dry this week. There will be little variance in the Central Pacific synoptic pattern the next several days so these summertime conditions will be the general theme through the remainder of August.
The southern approach of a northern trough axis will reach the state's northern offshore waters tomorrow and Tuesday. This will weaken the northeast-to-east ridge enough to cause a brief interruption to recent moderate to locally strong (oceanic) trade flow. Monday through Wednesday's weakened winds will veer a bit more to the east southeast. Shortwave energy diving down around the base of the trough later in the week will assist in keeping stronger trades at bay through the last few days of the month. Weaker trade flow will allow local breezes to become more dominant. Thus, early sun will likely lead to mid to late afternoon into early evening cloud build up and scattered showers over Big Island Kona and upslope leeward mauka over Oahu and Kauai. Models are forecasting a minor increase in moisture moving up from the southeast and passing across Big Island tomorrow through Tuesday. This higher surge of moisture through a deeper boundary layer may enhance afternoon Kona slope showers early this week. The mid layers remain very dry across the remainder of the chain so, other than localized afternoon breeze activity, the only other rain producer would have to be from brief terrain-enhanced windward upslope mauka showers.

Aviation

Stable, moderate to breezy trades deliver clouds and showers windward and mauka through the period particularly overnight and during the early morning hours. Isolated MVFR within showers. Otherwise, VFR prevails.
No AIRMETs are in effect.

Marine

A ridge of high pressure north of the Hawaiian Islands will continue to produce fresh to locally strong trades today. A Small Craft Advisory (SCA) remains in effect for the windier waters of Maui County and the Big Island through 6 PM.
Small overlapping south swells and surf heights will continue to slowly decline into Monday. A series of small long period south swells will arrive by Tuesday, boosting south shore surf heights through Friday.
Surf along north and west facing shores will remain nearly flat while surf along east facing shores will continue to have trade wind driven chop for the next few days.

Fire weather

The lack of rain and lower humidity will maintain elevated fire weather concerns. Other than the typical high terrain channeled winds, many locations will experience light to low end moderate trades or afternoon sea breezes/overnight land breezes. While some leeward locales will experience afternoon humidities falling under 50 percent, lighter winds during this time will somewhat diminish the fire threat. Regional scale winds remain the key parameter that will need to be closely monitored. Inversion heights will undergo little change so the main driver of wind will be supported in the large scale. Wind speeds are expected to fall off by tomorrow in response to a northern trough weakening the gradient produced by eastern high pressure. As this trough pulls back further north at mid week, trades may slightly increase to more typical moderate speeds Wednesday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov