West Side

Today: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 86. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 69 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 81 to 86. Northwest winds around 10 mph. Chance of rain 50 percent.

South Side

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 88. North winds up to 20 mph increasing to 15 to 20 mph in the afternoon. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 69 to 77. North winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

Wednesday: Mostly sunny early in the morning then becoming mostly cloudy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs around 88. Light winds becoming northwest up to 10 mph in the afternoon. Chance of rain 40 percent.

North Shore

Today: Mostly sunny with isolated showers. Highs 80 to 87 near the shore to around 69 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 73 near the shore to around 54 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Wednesday: Partly sunny with scattered showers. Highs 81 to 88 near the shore to around 69 near 5000 feet. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 50 percent.

Central Maui

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 81 to 87. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 69 to 74. Northeast winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 82 to 89. Light winds becoming north around 10 mph in the afternoon. Chance of rain 50 percent.

Upcountry

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 69 at the visitor center to around 72 at the summit. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 45 to 56. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers. Highs around 67 at the visitor center to around 72 at the summit. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

East Maui

Today: Mostly sunny with isolated showers. Highs 80 to 87 near the shore to around 69 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 73 near the shore to around 54 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Wednesday: Partly sunny with scattered showers. Highs 81 to 88 near the shore to around 69 near 5000 feet. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 50 percent.

Lanai City

Today: Breezy. Mostly sunny with isolated showers. Highs 74 to 83. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Lows 64 to 69. Northeast winds 15 to 25 mph decreasing to up to 20 mph after midnight.

Wednesday: Mostly sunny early in the morning then becoming mostly cloudy. Scattered showers in the late morning and afternoon. Highs 74 to 82. Light winds. Chance of rain 50 percent.

Kaunakakai

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 74 to 90. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 61 to 75. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 75 to 91. North winds 10 to 15 mph shifting to the west in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The high pressure ridge north of the islands will weaken over the next several days, decreasing trade wind speeds especially as the remnants of former Tropical Cyclone Gil drifts westward, passing just north of the Hawaiian Islands on Wednesday and Thursday. Warm and very humid conditions with an increase in island shower activity will accompany Gil's passage. Tropical Cyclone Henriette will also drift westward, passing just north of the islands producing similar lighter hybrid sea breeze and trade winds, along with very warm and humid conditions from Sunday through Monday.

Discussion

Looking into the big picture of the GOES satellite imagery this morning we see just a few fairly stable bands of stratocumulus clouds upstream of the Hawaiian Islands. The upper level ridge remains anchored over the Hawaii Region today with subsidence (downward moving air) temperature inversion heights hovering around the 5,000 foot elevation level. Inversion heights at this low level will continue to cap vertical cloud development and limit any shower activity across the state today and tonight. A large rotating band of clouds near 23N 147W, associated with the remnants of former Tropical Cyclone Gil, will continue to drift westward over the next few days. This unstable and very humid air mass will pass just north of the Hawaiian Islands from Wednesday through Thursday, disrupting the trade wind flow and producing very warm and humid weather across the state. Clouds and shower will be enhanced a bit during this time period.
The challenge with this rainfall forecast are directly tied to changes in the forcing mechanism for rainfall production. As the trade winds diminish the more typical windward mountain lifting pattern will switch into a more hybrid light trade wind sea breeze island heating driven pattern. In this hybrid sea breeze pattern island interior and typically drier leeward sections will see more afternoon cloud and shower development. High boundary layer moisture levels with surface dew point temperatures in the low 70s and temperature inversion heights ranging from 8,000 to 9,000 feet will aid in convective heating driven shower development from Wednesday through Thursday. Any of these developing slow moving showers could produce brief locally heavy shower activity in some leeward areas, particularly along the Kona slopes of the Big Island as low level moisture mixes above the inversion height.
Drier conditions return briefly with moderate trade winds on Friday and Saturday. Long range global models and National Hurricane Center forecasts show another tropical system, currently Tropical Storm Henriette, passing just north of the islands from Sunday through Monday, once again disrupting trade winds and producing warm and very humid weather. Stay tuned for weather forecast updates as the track and intensity of Henriette will likely change over time.

Aviation

Trade winds will begin to decrease through the day for most areas. Overall stable conditions will keep clouds and showers to minimum into the evening hours. A deep tide of tropical moisture will sweep through the islands as the remnants of former Tropical Cyclone Gil drifts westward, passing just north of the state. Sea breezes will expand in coverage on Wednesday with increasing clouds and showers starting after midnight tonight through Thursday.
No AIRMETs in effect and none are expected until Wednesday where AIRMET Sierra for mountain obscurations are possible.

Marine

Trade winds will weaken in response to surface high pressure centered far north of the islands drifting further northeast through the week. The remnants of former Tropical Cyclone Gil are forecast to pass across the north offshore waters from tonight through Thursday. This will briefly disrupt mid week trades with its western passage. Trades will return and strengthen by Friday as the pressure gradient tightens back up north of the state.
The moderate size, long period south swell that peaked late last night boosted surf along many south-facing shores to High Surf Advisory (HSA) heights. South surf is expected to briefly fall below advisory levels later today. Another south swell arriving late Wednesday or early Thursday will pick south-facing surf back up to HSA levels.
A moderate, medium to long period east swell moving in from what was once Tropical Cyclone Gil, in tandem with short period trade wind wave chop, will peak east-facing shore surf to near advisory levels today.
A small, medium period northwest swell originating from former Typhoon Krosa in the West Pacific is bumping up surf a bit along north-facing shores. A small size, medium to long period northwest swell is scheduled to arrive late Wednesday into Thursday that will keep northern surf from going completely flat.

Fire weather

Humidity levels will show increasing trends with gradually decreasing winds today. The trade wind inversion heights will hover around the 4,500 to 5,500 foot elevation level with very low relative humidities continuing near the inversion level along the upper elevations of Haleakala on Maui and the mid to upper slopes of the Big Island. Elevated fire weather concerns will continue in these areas through the afternoon hours. Humidity levels will increase dramatically as a tide of tropical moisture sweeps into the islands later tonight through Thursday as the remnants of former Tropical Cyclone Gil drifts westward and passes just north of the Hawaiian Islands. Another round of deep tropical moisture will sweep through the islands from Sunday into Monday as Henriette follows a similar path.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for south facing shores of all islands.

Data Courtesy of NOAA.gov