West Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 72 near the shore to around 64 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Wednesday: Sunny and breezy. Highs 84 to 89 near the shore to around 75 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 20 mph in the afternoon.

Wednesday Night: Mostly clear. Lows around 73 near the shore to around 65 above 3000 feet. Northeast winds 10 to 15 mph decreasing to up to 15 mph after midnight.

South Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 69 to 75. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny. Breezy. Isolated showers in the morning. Highs 79 to 88. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Wednesday Night: Breezy. Partly cloudy with isolated showers. Lows 70 to 76. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Occasional showers in the evening, then scattered showers after midnight. Lows around 67 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain 90 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 68 to 81. Northeast winds 10 to 25 mph. Chance of rain 40 percent.

Wednesday Night: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 66 to 71 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Lows 64 to 74. Northeast winds up to 20 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs 68 to 84. East winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy. Breezy. Occasional showers in the evening, then scattered showers after midnight. Lows 65 to 75. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 84. Northeast winds 10 to 20 mph. Chance of rain 30 percent.

Wednesday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 66 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trade winds will prevail through much of the week as surface high pressure holds north of the state. Pockets of moisture moving in the trades will focus rainfall over windward and mauka areas with showers briefly passing over leeward areas. An area of deeper moisture may enhance showers on windward Big Island Friday and Saturday.

Discussion

Breezy and stable trade winds continue this afternoon. Robust high pressure several hundred miles north of the state is driving the trade winds, and mid to upper level ridging building overhead from the north is producing an inversion based between 6,000 to 7,500 feet. Under these stable conditions, showers have been largely confined to windward slopes where generally less than one quarter of an inch of rainfall has been observed today.
Shower activity will increase tonight within the breezy trade wind flow. A band of shallow moisture will fill in across windward Kauai and Oahu through the remainder of the afternoon and likely drift southward to Maui overnight. Some of these showers will periodically spill over to leeward areas on the strong trades, though rainfall totals will be modest due to the stable conditions.
Little change is expected through at Thursday. Trades will remain breezy as a surface ridge holds to the north, and additional pockets of moisture will focus showers over windward and mauka areas.
Some increase rainfall is likely for Friday and Saturday, mainly across windward Big Island. The National Hurricane Center continues to indicate a high chance of tropical cyclone development far southeast of the state within a few days. Guidance suggests that any tropical cyclone would have a high chance of passing well south of the islands, but the GFS and ECMWF are showing a broad field of deep moisture along the flanks of this feature moving over windward Big Island. The models differ slightly on the timing of the increased moisture. The GFS is running about 12 hours faster than the ECMWF by increasing showers as early as Friday morning and clearing the moisture Saturday. A tropical cyclone passing to the south could also lead to a period of stronger trade winds this weekend, though confidence in that possibility is low at this time.

Aviation

Moderate to locally strong trade winds continue across the region. Clouds and showers will continue to be focused over the windward slopes, but the strong winds could carry some showers to leeward areas at times. Generally VFR conditions are expected with only brief MVFR possible with any passing -SHRA.
AIRMET Tango remains in effect due to the mechanical turbulence to the lee of the mountains below 8000 feet. Anticipate this AIRMET to remain posted beyond 24 hours.

Marine

Fresh to strong trade winds will persist for most of the week across most coastal waters as high pressure remains in place north of the region. An advanced scatterometer (ASCAT) pass earlier today showed Small Craft Advisory (SCA) level winds in the typically windy channels. However, with another small increase in winds possible tonight, the SCA was left intact and remains in effect through Wednesday for now. While winds may decrease again across some northern zones on Thursday, at the same time an incoming northwest swell is likely to produce 10 ft seas across portions of the coastal waters once again, so refinements to the SCA are likely later this week. Additionally, from Thursday through early this weekend, a broad area of low pressure with high potential to develop into a tropical cyclone according to National Hurricane Center forecasts will approach and pass south of the islands, potentially enhancing winds over far southeast waters.
Surf along north- and west-facing shores will continue to decrease through Wednesday as a moderate, north-northwest swell fades and shifts more northerly, though another small long period north- northwest reinforcement arrives tonight. Another more significant moderate, long-period northwest swell will arrive Wednesday night into Thursday morning and will likely push north and west shore surf back to advisory levels for Thursday into Friday. An additional medium-period swell moderate swell is expected to fill in on Saturday, likely prolonging moderate to large surf action into the weekend.
A tiny long-period reinforcing swell is arriving this evening, but south shore surf will be small to tiny through much of the week with little southerly background energy reaching the islands. East-facing shores will see continued moderate trade wind swell as strong northeast winds remain. Surf along east-facing shores will stay elevated and choppy through much of the week with the trades.

Fire weather

Breezy winds during the next several days will produce moderate fire weather conditions since recent rainfall has likely limited the widespread availability of receptive fuels. The inversion near Big Island will range from 6000 to 8000 ft over the next few days.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov