West Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 71 to 76 near the shore to around 64 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 85 to 91 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy. Lows 70 to 75 near the shore to around 63 above 3000 feet. East winds up to 15 mph.

South Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 72 to 78. East winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 79 to 89. East winds 10 to 15 mph. Chance of rain 90 percent.

Wednesday Night: Breezy. Partly cloudy with scattered showers. Lows 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 66 to 71 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Wednesday: Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 73 to 81 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows 65 to 70 in the valleys to around 61 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 75. East winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 86. East winds up to 15 mph. Chance of rain 70 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 62 to 75. East winds up to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Scattered showers in the evening, then occasional showers after midnight. Lows 68 to 78. East winds 10 to 15 mph. Chance of rain near 100 percent.

Wednesday: Occasional showers in the morning, then numerous showers in the afternoon. Highs 76 to 85. East winds 10 to 15 mph. Chance of rain near 100 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 67 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to breezy trades deliver showers windward and mauka into next week.

Discussion

Despite a deep layer of dry mid-level air beneath the resident subtropical ridge, PWATs checked in at 1.63″ in Lihue and 1.80″ in Hilo this afternoon. This is a testament to rich boundary layer moisture that also has sea level dewpoints hovering around a muggy 70F. The afternoon Hilo sounding also showed light SE flow through the depth of this layer which will delay the exit of the resident batch of moisture until Wednesday. Winds in this layer are, however, notably more backed than this morning, a sign that more uniformly easterly trades are returning. Stage is then set for a return to high stability and a drier trade wind pattern by Thursday as 500mb heights build to 591dm and PWATs gradually decline to around 1 inch. A weakening TC Fausto then enters the picture early next week with guidance generally tracking the system near or north of the islands during the mid- week period.

Aviation

Radar and satellite show showers over most windward sites with scattered showers making it to leeward sites. This will continue into the evening, tapering off from east to west overnight. Moderate trades will continue.
AIRMET Sierra is in effect for the windward side of all islands due to low clouds mostly due to showers. This is expected to continue until at least the early evening hours, and should clear from east to west overnight.

Marine

Moderate trades will persist through this evening. As broad, weak troughing exits to the west and the strong high to the far northeast takes over, trades will strengthen to fresh to locally strong speeds late tonight into Wednesday. A Small Craft Advisory (SCA) has been issued for the typical windier channels and waters around Maui and the Big Island starting from late tonight through Wednesday night. Trades might strengthen another notch late Thursday into Friday with widespread strong trade winds possible towards the end of the work week as the high to the far northeast strengthens and edges west-southwest.
The current medium-period south-southeast swell producing above average surf along south-facing shores this afternoon will gradually fade over the next few days. The next notable incoming south swell was generated by a powerful low pressure system that tracked eastward well south of Tasmania and New Zealand last week. OSCAT pass showed a wide fetch of storm-force winds with altimeter passes showing seas above 50 feet. This should translate into very long period forerunners arriving as early as early Wednesday morning, steadily filling in throughout the day, and peaking on Thursday out of the south-southwest. The very long- period energy will make for inconsistent, but powerful waves when they arrive. Surf should reach High Surf Advisory (HSA) thresholds by Thursday, then reinforcing long-period swell energy may allow HSA conditions to persist through the weekend.
Surf along east-facing shores will remain slightly below seasonal levels through the evening due to the weaker trades upstream of the islands. The Hilo buoy continues to show a small, medium- period east swell filling in this afternoon, which was likely generated by former TC Elida. This swell should peak on Wednesday with near seasonal level surf. Stronger trade winds will also support an increase of short-period energy by Wednesday. This weekend, larger surf generated by Hurricane Fausto is possible and could bring advisory level surf along east facing shores.
Surf along north-facing shores will remain at flat to tiny levels through the weekend.

HFO Watches/Warnings/Advisories

Small Craft Advisory from midnight tonight to 6 AM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov