West Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 67 to 72 near the shore to around 60 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 88 near the shore to around 74 above 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy with isolated showers. Lows 67 to 72 near the shore to around 60 above 3000 feet. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 70. Northeast winds around 15 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 79 to 87. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Lows 61 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 80 percent.

Friday: Mostly cloudy with numerous showers. Highs 73 to 80 in the valleys to around 64 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy with numerous showers. Lows 61 to 68 in the valleys to around 58 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 71. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 84. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 63 to 71. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 73. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 83. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 63 to 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A typical trade wind pattern will persist over the next several days. The only subtle fluctuations will come in the way of more trade-sheltered local light breeze development and primarily windward enhanced rainfall based upon periodic pockets of higher moisture advecting in on the trades. Better organized windward showers may spill over into leeward communities. Clear morning skies may also lead to enhanced afternoon leeward slope showers, especially over regions that experience more efficient sea breeze behavior.

Discussion

Afternoon satellite and radar have shown a decrease in shower activity throughout the day. A couple of causations could be more subsidence brought on by western upper ridging advancing into the area along with an influx of slightly drier lower level air. Today's widespread rainfall has been very light with the majority of the highest windward totals coming in at under a couple tenths of an inch. Similar weather of cloudier skies and intermittent showers with higher rainfall being focused along windward mauka exposures can be expected through the middle of the month.
In the synoptic, broad upper level toughing over the Hawaiian Islands is exiting stage right as a large upper ridge builds in from the west northwest the next couple of days. This will maintain a more shallow boundary layer as subsidence lowers the mid-level inversion. Other than a few short lived higher bouts of moisture riding in around the southeastern periphery of the upper ridge, 850-700 mb layer moisture will generally be more dry than wet (or under 50% relative humidity) through Saturday. The higher moisture is progged to remain north of the islands with Friday's greatest rain probabilities being confined to Kauai. Mainly clear skies will lead to more sea breeze (shower) activity across such regions as leeward Big Island and South/Upcountry Maui the next couple of days. Leeward plains such as Ewa on Oahu and downslope West Kauai will heat up under mostly sunny conditions. Afternoon mid to upper 80s may attain maximum temperature records within these areas and urban centers (89 F is Honolulu's Friday maximum temperature record).
As the upper high moves east to the north of the islands, more moisture rich air is forecast to move across the islands from the east northeast early to mid next week. The surface high will settle far northeast of the state and this will guarantee continued breezy trades through the middle of next week. The amount of statewide rain will primarily depend upon the strength and influence of the upper ridge centered north of the islands. Ample moisture will be in place, so daily rainfall will be dependent upon the ebb and flow of inversion height/subsidence (or lack thereof). Global deterministic NWP guidance, as well as respective ensemble member patterns, lean toward a more wet start to early next week with each subsequent day having slightly higher rain probabilities. In comparison to the next couple of relatively drier days, next week's rain behavior can best be classified as more wet trades…widespread rain of low accumulation. Latter period rainfall (from Tuesday onward) will become more moderate to locally heavy over windward exposures.

Aviation

High pressure to the north along with a stable atmosphere will allow a breezy trade wind pattern to continue through the next several days. Showers will primarily focus over windward and mountain areas as well as the night time hours. Periods of enhanced shower activity could lead to temporary MVFR conditions at times, however VFR conditions will likely prevail.
AIRMET Tango remains in effect for moderate low-level turbulence over and immediately SW through NW of all island mountains due to the locally breezy trade winds. This AIRMET will likely continue for the next few days. AIRMET Sierra for mountain obscuration is not currently in effect but could be in effect tonight for windward and mountain areas of all islands as showers return.

Marine

A surface ridge that is currently situated north of the islands will remain in place through early next week, allowing fresh to locally strong easterly trade winds to persist for at least the next several days. A Small Craft Advisory (SCA) currently remains in effect for the typical windy waters and channels around Maui County and the Big Island. This SCA will likely need to be extended in time into next week.
Surf along south-facing shores will remain below average into Friday as a small background south swell lingers. A fresh long- period south-southwest swell is expected to arrive Friday, bringing an upward trend with above-average surf this weekend. The forecast remains on track with this south swell, so minimal changes have been made. The latest guidance continues to indicate that forerunners will begin filling in Friday, with the swell peaking late Saturday through Sunday. This swell peaked above guidance at the American Samoa PacIOOS buoy earlier this week, and is expected to bring advisory-level surf to south facing shores.
Surf along exposed north and west-facing shores will gradually lower and slowly shift out of the north-northeast over the next several days. Surf along east-facing shores will remain rough and choppy throughout the next few days due to the trade winds, with heights hovering around average each day.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Kauai Now Weather is brought to you by Blue Hawaiian Helicopters.