Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 72 above 3000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Partly cloudy with isolated showers. Lows around 66 near the shore to around 56 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs around 83 near the shore to around 71 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 79 to 84. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 65. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 84. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 80 in the valleys to around 63 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy and breezy. Scattered showers early in the evening, then numerous showers late in the evening. Frequent showers after midnight. Lows 58 to 63 in the valleys to around 53 above 4000 feet. Northeast winds up to 15 mph increasing to 10 to 20 mph after midnight. Chance of rain 80 percent.

Saturday: Cloudy and breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 72 to 79 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

North Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 83. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 67. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 74 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 82. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 59 to 69. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 83. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will weaken slightly into the weekend. An upper trough over the region will help enhance shower coverage and rainfall intensity at times through tonight. Isolated thunderstorms are possible over portions of the Big Island today. A trend toward more stable and drier conditions is then expected this weekend, with lingering trade wind flow focusing showers across mainly windward and mauka areas.

Discussion

Current radar shows showers remain scattered across the state this morning in response to lingering trade wind flow and the weak upper low in the vicinity. Radar estimates show a few heavier showers remain embedded in the flow, especially across Oahu and Kauai.
Today through tonight…have increased the areal coverage of showers across the western half of the state, as an upper trough (associated with an upper low northeast of the state) begins to sweep in from the northwest. The dynamics associated with this upper trough will combine with a band of enhanced moisture (satellite imagery PW values 1.40″ to 1.50″) streaming into the state from the east. Low level streamline convergence and cooling temperatures moving in aloft, will help support embedded higher rainfall rates across the islands at times today. Stability indices (SW index) and thunderstorm probabilities show enough instability across mainly the eastern end of the state to support a chance of afternoon convection. Some afternoon sun and steepening lapse rates should enhance the chances over Big Island, therefore will maintain the isolated thunderstorm chance over leeward and upslope portions. Otherwise trade winds should maintain a majority of showers to favored windward areas.
The persistent upper low, which has been anchored over the region since earlier in the week, will continue to drift northeastward tonight. This will allow a narrow upper ridge to approach from the northwest tonight, and begin the trend toward drier and more stable conditions.
Saturday through Sunday…a strong area of high pressure well north of the islands will maintain trade winds through the weekend. The winds will trend more southeast and weaken slightly Sunday, as a surface boundary approaches from the northwest. At upper levels, the low will continue to slowly drift northeast of the state allowing an upper ridge and more stable airmass to organize across the islands. The fairly stable and dry airmass (modeled PW values 1.30″ or less) will maintain a majority of showers across windward areas with the greatest areal coverage of showers expected at night through early morning.
Monday through next week…global models are in fairly consistent agreement with surface and upper level features influencing the state through the first half of the week. A narrow upper level ridge, which developed over the islands over the weekend, will slowly push eastward through the week while a weakly organized upper trough, associated with a strong upper low well northwest of the state, slowly drifts eastward. At the surface, low pressure moving well north of the state will drag a front into the islands through midweek, potentially increasing shower coverage and rainfall rates Tuesday and Wednesday. The second half of the week, model solutions begin to diverge with the overall evolution and movement of surface and upper level features.

Aviation

Moderate to locally breezy trade winds will continue today. Current satellite imagery and radar show scattered clouds and showers moving through the islands from the east with the focus of the showers being over windward and mauka areas. A few thunderstorms have been observed over the waters far South and East of Oahu and Kauai and are expected to stay offshore. An isolated thunderstorm will remain possible over the Big Island slopes this afternoon as instability from an upper level low lingers. Shower activity is expected to continue favoring windward and mauka areas through the TAF period with a few showers drifting to leeward areas. A few of these showers will bring isolated MVFR conditions. Overall VFR conditions will prevail.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of higher terrain across all islands.

Marine

A 1032 mb high pressure cell centered approximately 1,200 miles north northeast of Oahu will become absorbed by a new high expanding down from the Aleutian Islands. This will weaken the high and relax the upstream pressure gradient over the islands as the high slowly meanders southeast Saturday. The current SCA has been scaled back area-wise to now just include the Alenuihaha and Pailolo Channels and Maalaea Bay. Winds should briefly drop below SCA thresholds across the entire region this evening. Following a Saturday of relatively light trade flow, a trough developing west of the state along with a surface high establishing itself far northeast of the area will veer returning fresh to locally strong trades toward the southeast Sunday into Tuesday.
A slowly diminishing moderate size, short period northeast (30-40 degree) swell that popped in yesterday will maintain chest to near head high surf along many north and northeast-facing shorelines through the day. A small, medium period northwest (320 degree) swell is scheduled to arrive later today as it has not shown up at the far northwest offshore buoys before sunrise. This swell is forecast to fill in through tonight and peak on Saturday. This swell will hold waist to near head high surf along many north-facing shores, near knee to waist high surf along west-facing shores Saturday. East-facing shores will experience continued choppy conditions through today in response to several days of an upstream fresh trade fetch. Surf along east-facing shores will slowly subside going into this weekend as trades fall off a notch. Small, background south swell energy will maintain knee to chest high surf along many southern shores. A very small, medium period south southwest bump in swell arriving this morning will result in a small boost in weekend surf.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

Data Courtesy of NOAA.gov