West Side

Today: Sunny and breezy. Highs 77 to 89. East winds up to 20 mph.

Tonight: Mostly clear. Breezy. Isolated showers in the evening. Lows 67 to 76. East winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 88. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

South Side

Today: Sunny and breezy. Highs 79 to 92. North winds up to 15 mph shifting to the northeast in the afternoon.

Tonight: Mostly clear. Breezy. Lows 68 to 74. North winds up to 20 mph decreasing to up to 10 mph after midnight.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 90. North winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

North Shore

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 88 near the shore to around 71 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 72 near the shore to around 55 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 82 to 88 near the shore to around 70 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 30 percent.

Central Maui

Today: Sunny and breezy. Highs 83 to 91. Northeast winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Lows around 71. Northeast winds 10 to 20 mph decreasing to up to 10 mph after midnight.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 88. Northeast winds up to 10 mph. Chance of rain 30 percent.

Upcountry

Today: Breezy. Sunny with isolated showers. Highs around 69 at the visitor center to around 67 at the summit. East winds up to 20 mph becoming 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 50 at the visitor center to around 45 at the summit. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the afternoon. Highs 56 to 74. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

East Maui

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 88 near the shore to around 71 near 5000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 72 near the shore to around 55 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 82 to 88 near the shore to around 70 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 30 percent.

Lanai City

Today: Sunny and breezy. Highs 73 to 84. Northeast winds up to 20 mph.

Tonight: Mostly clear. Breezy. Lows 62 to 68. Northeast winds 10 to 20 mph.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 72 to 83. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Kaunakakai

Today: Sunny and breezy. Highs 74 to 90. East winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Isolated showers in the evening. Lows 60 to 75. East winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 74 to 89. Northeast winds 10 to 20 mph. Chance of rain 30 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 a slight increase in island shower activity will accompany Gil's passage.

Discussion

The satellite picture this morning shows a large band of stable stratocumulus clouds moving from east to west into all islands. A strong subsidence temperature inversion aloft will tend to decrease cloud cover and shower activity later this morning. A large rotating band of clouds near 20N 140W, 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. However, much of these shower impacts will depend on the track and how close this system gets to the Hawaiian Islands.
The breezy weather pattern will change today through Tuesday as the high pressure ridge north of the state weakens. Moderate to locally breezy trade winds today will noticeably decrease in strength into the light to moderate range over the next 24 to 36 hours. A high pressure ridge aloft will bring down enough subsidence (downward moving air) to keep shower activity to minimum levels through Tuesday. Expect very warm and humid conditions from Tuesday night through Thursday as the remnants of former Tropical Cyclone Gil continue to weaken as it approaches the islands from the east. This remnant tropical system will pass just north of the Hawaiian Islands, cutting off trade winds and increasing island shower trends especially over leeward areas. The latest global weather models take the strongest part of this system far enough north to limit significant shower activity.
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 shower development from Wednesday through Thursday. Any of these developing slow moving showers could produce brief locally heavy shower activity in some leeward areas.
Drier conditions return briefly with moderate trade winds on Friday and Saturday. Long range global models currently show another weakening tropical system, currently Tropical Depression Eight-E, will pass 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 of this next approaching tropical system will likely change over time.

Aviation

Moderate to locally breezy trade winds will continue today before decreasing into the light to moderate range by Tuesday afternoon. Windward cloud cover and brief passing showers will diminish later this morning as more stable trends move over the Hawaii Region.
AIRMET Tango remains in effect for moderate low level turbulence over and immediately south through west of island mountains. This AIRMET will likely be cancelled later today as wind speeds aloft decrease.

Marine

High pressure north of the state will weaken and drift eastward through Tuesday. Trade wind speeds will gradually lower through the middle of the week as the remnants of former Tropical Cyclone Gil passes to the northeast of the state, then strengthen out of the east southeast late Thursday through the end of the week. The Small Craft Advisory (SCA) has been extended for the windier waters and channels around Maui County and the Big Island through tonight.
A moderate, long period south swell has begun to slowly fill in overnight and is expected to peak below High Surf Advisory (HSA) criteria this evening into Tuesday before declining Wednesday. Another swell is expected from a low formed south of New Zealand at the end of July, that measured seas of 35 to 40 feet aimed towards Hawaii. This swell is expected to build on Thursday and hold through the end of the week which could get near HSA criteria at its peak.
Short period trade wind swell will keep east facing shores elevated and choppy today due to strong trade winds. By late this evening into Tuesday, a moderate, medium to long period east swell is expected to fill in from the energy from former Tropical Cyclone Gil.
A small, medium period northwest swell originating from Typhoon Krosa in the western Pacific will bring a small bump up in surf along north facing shores through today. Another bump is expected as a small, medium to long period northwest swell looks to fill in Thursday and Friday.

Fire weather

Humidity levels will show increasing trends with gradually decreasing winds from today through Tuesday. The trade wind inversion heights will drop to around 5000 to 6000 feet with very low relative humidity 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 Tuesday afternoon. Humidity levels will increase dramatically from Tuesday night through Thursday as the remnants of former Tropical Cyclone Gil drifting westward, passes just north of the Hawaiian Islands.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for typical windier waters and channels around Maui and the Big Island.

Data Courtesy of NOAA.gov