Photo Credit: Braden Jarvis

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs 88 to 93 near the shore to around 79 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Isolated showers in the evening. Lows around 73 near the shore to around 64 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Thursday: Sunny and breezy. Highs 88 to 93 near the shore to around 79 above 3000 feet. East winds up to 20 mph.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 86 to 92. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 73 to 78. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Thursday: Sunny and breezy. A 20 percent chance of showers in the morning. Highs 85 to 92. Northeast winds 15 to 25 mph.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 75 to 87 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows 67 to 72 in the valleys to around 61 above 4000 feet. East winds 10 to 25 mph. Chance of rain 40 percent.

Thursday: Breezy. Mostly sunny with a 20 percent chance of showers. Highs 75 to 87 in the valleys to around 68 above 4000 feet. East winds 10 to 20 mph.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 91. East winds up to 15 mph. Chance of rain 40 percent.

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

Thursday: Sunny and breezy. A 20 percent chance of showers in the morning. Highs 78 to 90. East winds up to 20 mph.

East Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 89. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers. Lows 67 to 80. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny. Breezy. A 20 percent chance of showers in the morning. Highs 76 to 89. East winds 10 to 20 mph.

Detailed Forecast

Synopsis

The trade winds are expected to become locally strong later today and tonight through Thursday. Low clouds and showers carried by the trade winds will remain focused over windward and mauka areas this morning. Much drier conditions are forecast to spread from east to west across the island chain from this afternoon through tonight. The combination of the gusty trade winds and very low humidity values will elevate fire weather concerns on Thursday. Expect a more typical trade weather pattern to return heading into the Labor Day Holiday Weekend.

Discussion

A 1030 mb surface high pressure system located near 36N 143W, or slightly less than 1400 miles northeast of Honolulu, is drifting slowly westward. This feature is causing the pressure gradient to gradually tighten across the region. As a result, moderate to locally breezy trade winds are evident over most of the state early this morning.
Satellite derived precipitable water (PW) values show an area of increased moisture over the eastern end of the island chain this morning. This area will likely continue pushing westward over the state today. As a result, low clouds and showers carried by the trade winds will be transported into windward facing sections of most of the islands, especially this morning. The trades may also carry a few brief showers over to leeward sections of some of the smaller islands, mainly this morning.
The forecast guidance shows that the surface high will drift westward and build slightly through mid-week. This will likely cause breezy to locally windy conditions to eventually develop during the next couple of days. At the moment, we do not anticipate the need for a Wind Advisory for any islands today. However, a Wind Advisory will likely be a needed over many locations (especially the islands of Maui County and the Big Island) starting tonight or Thursday.
In addition, the models are showing that once the area of increased moisture pushes west the islands later today, much drier conditions will develop heading into tonight / Thursday. An upper-level ridge is also expected to build above the islands through Thursday. This will provide a more stable atmosphere, and cause the trade wind inversion to lower. This will mean reduced relative humidity values and fewer showers at the same time the winds are the strongest. This combination of increasing winds and very dry conditions will elevate fire weather concerns. Therefore, a Fire Weather Watch remains in effect for Thursday. See the Fire Weather Discussion below, as well as the Fire Weather Watch product for additional information.
The surface high pressure system and the upper-level ridge are expected to gradually lift north from Friday into the weekend. This will likely allow the surface winds to weaken somewhat by the end of the week. In addition, the inversion height is expected to increase slightly. This may produce a more typical trade wind weather pattern with moderate to locally breezy trade winds as we head into the Labor Day Holiday Weekend. PW values are expected to increase back to near normal during this time, so anticipate a more typical coverage of low clouds and trade showers. This scenario would mean that low clouds and showers will favor windward and mauka areas, primarily during the nighttime and early morning hours.
Looking ahead, a surface trough approaching from the east is expected to weaken the pressure gradient starting Sunday. If so, this will likely cause the trade winds to weaken slightly from Sunday through early next week.

Aviation

The trades will strengthen to breezy levels today as high pressure to the distant northeast edges closer to the island chain. Low clouds and showers will bring some brief MVFR cigs/vsbys into windward slopes and coasts through mid morning, but predominantly VFR conditions are expected during the next 24 hours across the entire island chain.
AIRMET Tango remains in effect for low level turbulence over and downwind of the terrain of all islands. This AIRMET will likely continue through Thursday.

Marine

Fresh to strong easterly trades will become strong for all Hawaiian waters later today through Thursday night, then slowly ease Friday through Saturday as the ridge begins to weaken and a broad trough approaches from the east. Guidance continues to advertise light east-southeast winds Sunday through early next week as the broad trough moves into the area. Small Craft Advisory conditions has been expanded to include all waters through Thursday night. Seas will respond and become rough, with some of the windier channels and waters exceeding the 10 ft advisory level Thursday.
Surf along east facing shores will become rough later today through the second half of the week as the trades ramp up. Additionally, expect some groundswell mixed in with 9-10 second periods for the upcoming weekend from former Tropical Storm Irwin tracking westward across the eastern Pacific. Surf heights should stay below the 10 ft (faces) advisory level through the peak of this event Thursday through Saturday. A downward trend is expected Sunday into early next week as the trades relax.
Surf along south facing shores will remain small through the weekend as overlapping background level long-period southerly pulses move through. For the extended, guidance is advertising a solid south swell arriving next week (Monday night through midweek). A band of gales focused at the state down the 180-190 degree directional band east of New Zealand is forecast to nose northward over the next 24 h with seas climbing to around 30 ft. Expect a late season event with heights potentially nearing the advisory level during the peak late Tuesday through Wednesday.
Surf along exposed north and west facing shores will trend up again this weekend as a small west-northwest (300-310 degrees) swell arrives. This will be in response to a storm-force low (former TC Damrey) racing eastward toward the Date Line from Japan over the past couple of days.

Fire weather

Breezy to locally strong trade winds will develop later today and tonight through Thursday. The relatively moist conditions that are currently in place across portions of the island chain will eventually push west of the state later today. By Thursday morning, significantly lower dew points are expected to spread across the state, which will result in much lower humidity values by the afternoon hours. Therefore, a Fire Weather Watch remains in effect for Thursday.
Red Flag conditions are characterized by sustained winds of 20 mph or greater, dry fuels, and afternoon relative humidity values below 45 percent, which are likely to be in place Thursday. It is important to note that the winds for this event WILL NOT be comparable in strength to the August 8, 2023 event, where wind gusts of over 60 mph were observed. The latest forecast for Thursday is for trade winds of 15 to 30 mph with gusts of 40 to 50 mph, with the strongest wind gusts likely downwind / leeward of the higher terrain on the islands of Maui County and the Big Island.

HFO Watches/Warnings/Advisories

Fire Weather Watch from Thursday morning through Thursday afternoon for Kauai Leeward, Oahu South Shore, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Molokai Leeward, Lanai Makai, Lanai Mauka, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, South Big Island, Kohala, Big Island Interior.
Small Craft Advisory until 6 AM HST Friday for all Hawaiian waters.

Data Courtesy of NOAA.gov