Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 84 near the shore to around 69 above 3000 feet. East winds 15 to 20 mph with gusts to 45 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 67 near the shore to around 57 above 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers. Highs around 83 near the shore to around 67 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 75 to 82. East winds 20 to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 66. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Sunday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 81. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Occasional showers early in the morning, then scattered showers in the late morning and afternoon. Highs 70 to 79 in the valleys to around 60 above 4000 feet. East winds 15 to 25 mph with gusts to 50 mph. Chance of rain 80 percent.

Tonight: Breezy. Cloudy with occasional showers. Lows around 64 in the valleys to around 54 above 4000 feet. East winds 15 to 25 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 69 to 78 in the valleys to around 59 above 4000 feet. East winds 15 to 25 mph. Chance of rain 90 percent.

North Kaua’i

Today: Partly sunny. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 72 to 84. East winds 15 to 20 mph with gusts to 45 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 60 to 70. East winds 10 to 20 mph. Chance of rain 90 percent.

Sunday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 82. East winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Partly sunny. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 69 to 80. East winds 15 to 20 mph with gusts to 45 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 62 to 70. East winds 15 to 20 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 68 to 78. East winds 10 to 20 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

Strong, gusty trade winds will persist through today and then gradually weaken from Sunday through Tuesday, along with frequent showers. Lighter winds and relatively drier weather is expected by the middle of next week. A cut off low may develop from a deepening trough northwest of the islands late next week. This scenario would veer trades more southerly and introduce more widespread showers that may produce locally moderate to heavy periods of rain.

Discussion

The state's strong and gusty trade winds have been the direct result of a very tight pressure gradient created by a large near 1040 mb high centered approximately 1,000 miles north of the Hawaiian Islands. Overnight winds have remained strong, especially across exposed windward regions or at higher elevation such as through Oahu's Ko'olaus, Mount Haleakala and Big Island's north Kohala, where sustained winds remained 25 to 30 mph with frequent gusts to 40 mph. The Wind Advisory remains unchanged and in effect for these better windward exposed areas around the state through this afternoon. Organized showers may produce brief periods of strong gusty conditions with their passage.
Partly to mostly cloudy lower level conditions with mainly overcast and showery conditions at higher elevations the next few days. Precipitation chances will stay moderate to high over the weekend as showers move in from the east, especially along windward-facing coasts and slopes. While not receiving as much accumulated rain, downstream leeward locations will also experience frequent downpours. The region will remain under weak mid to upper level troughing the next several days with periodic pockets of higher 850-700 mb relative humidity streaming in on these easterly steering winds. A stationary mid and upper level low far northwest of the region and its associated trough extending north of the islands will help maintain an elevated subsidence inversion. Deep enough moisture with the resident atmosphere capped at near 10 kft will help support brief heavy showers. The low is forecast to weaken into a trough as it moves over the islands early next week. While relatively drier than this weekend, rain chances will remain modestly high early next week as a result of this passing trough axis along with a near-zonal orientated subtropical jet paralleling 20N providing ample diffluence aloft. This wetter theme is also supported by areas of higher 500 mb vorticity caught within the jet providing additional lift/instability. These are timed to pass across the islands this afternoon and again early Tuesday morning.
Model guidance suggests that wind speeds will slowly diminish this weekend as the slow eastern-moving large high north of the state gradually weakens. Local winds will potentially surge at times as shower bands pass through during the overnight hours. The high will weaken as it advances east early to mid next week. A weakness in the ridge north of the islands will create significantly lighter winds Tuesday and Wednesday. Mid to upper level warming brought on by slightly higher heights (or weakening upper troughing) will also contribute to relatively fewer showers. Forecast uncertainty is quite high beyond Wednesday as model solutions widely diverge on the evolution of a late week low possibly forming north of the state. Ensemble guidance from various models are leaning toward a kona low scenario by Thursday. If this cut off low feature does develop, then expect winds to veer more southerly with return bouts of moderate to heavy rainfall as southerly flow taps into a more moisture-rich southern environment.

Aviation

Strong high pressure north of the state will continue to drive breezy to windy trades through the weekend. Bands of low clouds and showers will continue to bring some MVFR cigs/vsbys into windward areas. Decaying showers will reach leeward areas at times as well, but predominantly VFR conditions should prevail here.
AIRMET Sierra remains in effect for mountain obscuration over windward Kauai, Oahu, Molokai, Maui and Big Island. These conditions should improve later this morning.
AIRMET Tango remains in effect for moderate to isolated severe low level turbulence over and downwind of the terrain of all islands. Little change is expected during the next 24 hours.

Marine

A strong surface high pressure north of the islands continues to drive strong to gale-force easterly trade winds across the coastal waters. This high will weaken as it slowly drifts south then east over the next few days. Despite the weakening high pressure, the gradient will still remain fairly tight over the island chain as it drifts closer to the state into the weekend. A Gale Warning remains in effect for the typically windier waters of Maui County and around the Big Island through the day, and will likely be downgraded to a Small Craft Advisory (SCA) through Sunday. Meanwhile, the SCA remains in effect for all remaining coastal waters through tonight due to a combination of strong winds and seas and will also likely be extended for majority of the zones through Sunday. The high will eventually weaken early to the middle of next week, with a weakness in the ridge north of the islands leading to much lighter winds Tuesday and Wednesday. The SCA will likely drop coinciding with the declining winds and seas.
East facing shores will continue to see elevated short period rough surf as the strong trade wind generated seas continue to impact the islands. A High Surf Advisory (HSA) has been extended for all exposed east facing shores through tonight. As trade winds gradually ease near and upstream of the state, the rough surf along east and exposed north facing shores will gradually decline throughout the weekend.
Surf along north facing shores will remain elevated due to areas exposed to the east wrap, as well as small northerly reinforcements. The second half of next week guidance suggests a low developing north of the state that could aim a moderate short to medium period north-northwest swell reaching the islands by Thursday and Friday.
For southern shores, small pulses of medium period south- southeast swell and long period southwest swell will move through over the next several days.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST this evening for Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
High Surf Advisory until 6 AM HST Sunday for Olomana, Maui Windward West, Kauai East, Kauai South, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Gale Warning 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