Photo Credit: Jeni Ji Cousins

West Side

Today: Isolated showers before noon. Mostly sunny, with a high near 85. Breezy, with an east northeast wind 14 to 21 mph, with gusts as high as 29 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Partly cloudy, with a low around 67. Breezy, with an east northeast wind 16 to 21 mph decreasing to 8 to 13 mph after midnight. Winds could gust as high as 29 mph. Chance of precipitation is 20%.

Sunday: Mostly sunny, with a high near 85. Breezy, with an east northeast wind 8 to 15 mph, with gusts as high as 21 mph.

South Side

Today: Isolated showers after 1pm. Mostly sunny, with a high near 85. Light and variable wind becoming west 5 to 8 mph in the afternoon. Chance of precipitation is 20%.

Tonight: Isolated showers before 7pm. Mostly clear, with a low around 66. West wind around 5 mph becoming calm in the evening. Chance of precipitation is 20%.

Sunday: Isolated showers after 1pm. Sunny, with a high near 84. Calm wind becoming west northwest around 6 mph in the afternoon. Chance of precipitation is 20%.

North Shore

Today: Scattered showers before 1pm. Mostly sunny, with a high near 84. Windy, with an east wind 18 to 25 mph, with gusts as high as 36 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers after 7pm. Mostly cloudy, with a low around 66. Windy, with an east wind 16 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Scattered showers before 1pm. Mostly sunny, with a high near 83. Windy, with an east wind 17 to 25 mph, with gusts as high as 36 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Central Maui

Today: Scattered showers before noon. Mostly sunny, with a high near 84. Breezy, with an east northeast wind 11 to 16 mph increasing to 17 to 22 mph in the morning. Winds could gust as high as 31 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 65. Breezy, with an east northeast wind 8 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Scattered showers before noon. Mostly sunny, with a high near 83. Windy, with an east northeast wind 8 to 13 mph increasing to 18 to 23 mph in the morning. Winds could gust as high as 32 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Upcountry

Today: Isolated showers after noon. Mostly sunny, with a high near 71. West wind 5 to 7 mph becoming calm in the afternoon. Chance of precipitation is 20%.

Tonight: Mostly clear, with a low around 56. Light and variable wind.

Sunday: Sunny, with a high near 71. Calm wind becoming west around 5 mph.

East Maui

Today: Showers likely, mainly before noon. Partly sunny, with a high near 82. Light and variable wind becoming east 5 to 10 mph in the morning. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 63. East wind 5 to 8 mph becoming south in the evening. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Sunday: Showers likely, mainly before noon. Partly sunny, with a high near 80. Breezy, with an east southeast wind 6 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Lanai City

Today: Isolated showers after noon. Mostly sunny, with a high near 74. Breezy, with a northeast wind 15 to 21 mph, with gusts as high as 29 mph. Chance of precipitation is 20%.

Tonight: Partly cloudy, with a low around 62. Breezy, with an east northeast wind 8 to 18 mph, with gusts as high as 25 mph.

Sunday: Isolated showers after noon. Mostly sunny, with a high near 75. Breezy, with an east northeast wind 8 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 20%.

Kaunakakai

Today: Isolated showers before noon. Mostly sunny, with a high near 82. Breezy, with an east northeast wind 11 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Partly cloudy, with a low around 70. Breezy, with an east northeast wind 9 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 20%.

Sunday: Isolated showers before noon. Mostly sunny, with a high near 82. Breezy, with an east wind 9 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

A high pressure ridge north of the islands will keep moderate to locally breezy trade wind weather in the forecast through Sunday. An upper level low drifting over the region will produce enhanced showers across all islands favoring windward and mountain areas. Trade winds will weaken and veer towards the southeast early next week as a cold front approaches the islands from the northwest. This front may stall out just north of Kauai on Wednesday with limited impacts to the local rainfall forecast.

Discussion

This mornings satellite imagery shows bands of cloud and showers drifting into the islands on the trade winds. An upper level low over the state will tend to enhance shower activity focused mainly over windward and mountain areas through the weekend. A few of the stronger showers may briefly drift leeward. Thunderstorms are developing in the offshore waters along the convergence plume west of the Big Island. Additional isolated thunderstorms may develop later today triggered by convective heating over the Big Island coastal and interior sections.
The upper low will drift south of the islands on Sunday, however a cold temperature pool aloft will linger over the state keeping enhanced windward showers in the forecast. By Monday a slow moving cold front approaching the islands from the northwest will begin to break down the ridge north of the region. Moderate trade winds will weaken and veer towards a more southeasterly direction. Lighter large scale winds will allow local scale land and sea breezes to develop through the middle of next week. Converging sea breezes and island heating will build clouds and showers over island mountain and interior sections each day with brief showers favoring afternoon to early evening hours.
An upper trough passing far north of the region will kick out the upper low south of the islands, causing it to move quickly towards the northeast on Monday night. This unstable low will pass over the island chain from late Monday into Tuesday. Expect another round of rain shower enhancement for all areas during this period. Isolated thunderstorms may develop during this time period.
Long range global model guidance continues to struggle on how close the cold front gets to the islands next week before it’s forward motion stalls out. The latest European (ECMWF) model brings the weakening frontal trough into the islands on Wednesday, while the latest American (GFS) model solution stalls the weak front just north of Kauai. The GFS solution also forms a prefrontal convergence zone of clouds and showers over the western half of the state from Tuesday to Wednesday.
This time of year cold fronts reaching the Hawaii region tend to be weaker and struggle to move into the islands. The forecast tendency here would be to expect these fronts to stall out sooner than the model forecasts, or to favor the less progressive model solution. This means we will lean towards the GFS solution with the weak frontal boundary stalling out just north of Kauai for now. Moderate trade winds will return from Thursday to Friday as a migratory high builds in north of the state with clouds and passing showers trending back to windward and mountain areas.

Aviation

High pressure north of the state will keep moderate to breezy trade winds in place through tonight. Clouds and showers will favor windward slopes and coasts, mainly at night and during the early morning hours. A few showers may spill leeward over the smaller islands at times, and a few showers and possibly a thunderstorm may affect the leeward Big Island slopes this afternoon. Some brief MVFR cigs/vsbys will be possible in showers across windward areas, although these conditions may be more prevalent over windward Big Island through the morning hours. Otherwise, prevailing VFR conditions are expected.
AIRMET Sierra remains in effect for mountain obscuration across windward sections of the Big Island. This AIRMET will likely continue through mid morning.
AIRMET TANGO remains in effect for low level turbulence over and downwind of the terrain of all islands. This AIRMET will likely continue through the weekend.

Marine

Surface high pressure north of the islands will keep a tight enough pressure gradient across the state to maintain fresh to locally strong trade winds this weekend. The Small Craft Advisory has been extended through Sunday afternoon to account for strong winds within those typically windier waters surrounding Maui County and south of the Big Island. As early week high pressure north of the area weakens and moves further east northeast of the state, trade speeds will begin to decrease late Sunday. Trades will weaken even further and veer southeast on Monday, becoming variable gentle breezes Tuesday ahead of an approaching weak front from the northwest.
Surf along all shores is expected to remain well under high surf advisory thresholds the next several days. A declining background northwest swell will hold small surf along north and west facing coasts through Sunday. The next west northwest swell will be arriving Monday night into Tuesday morning. This moderate, lower period swell will pick up Tuesday and Wednesday surf along most northern and western exposures. A slightly larger and longer period reinforcing west northwest swell may reach the islands late in the week. This swell will provide a boost to north and west coast surf Friday and Saturday with a slow decline from Sunday through Tuesday. A series of small, long period south southwest swells will continue to produce small surf along southern facing shorelines into next week. Eastern shore surf will remain small this weekend with surf heights falling even more going into the middle of next week as trades weaken and breezes become light south to variable.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov