West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 69 to 74 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 85 to 90 near the shore to around 77 above 3000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Wednesday Night: Mostly clear. Lows 70 to 75 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph.

South Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 89. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Occasional showers in the evening, then numerous showers after midnight. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Wednesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 84 in the valleys to around 66 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 73. East winds up to 10 mph. Chance of rain 70 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 87. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 65 to 74. East winds around 10 mph. Chance of rain 30 percent.

East Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 65 to 77. Northeast winds around 10 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers. Highs 74 to 86. Northeast winds around 10 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 65 to 77. Northeast winds around 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Light to moderate trades are expected over the next few days with showers favoring windward and mauka areas, particularly near both the eastern and western ends of the state. A brief period of drier weather Friday into the first half of the weekend will be followed by more overcast and wet weather early next week in response to an early November upper trough near the state.

Discussion

This afternoon, a weakening surface front is making its way eastward across the North Pacific, situated between two areas of high pressure far north and far northeast of the main Hawaiian Islands. This frontal boundary extends into the northern offshore waters this afternoon, but is expected to weaken over the next 12 to 24 hours. Meanwhile, troughing aloft stretches over the western end of the island chain, but latest regional satellite imagery shows that most showers and more extensive clouds associated with this feature are located well to the northeast, where much more instability exists aloft. Locally, CIMSS precipitable water imagery shows that a pocket of drier air is currently working its way over the smaller islands, while greater available moisture is located near developing troughs near both the far eastern and western ends of the state. Latest satellite and radar imagery supports this, with afternoon cloud buildups and a few showers over the Big Island, while low clouds and showers across the remaining islands have have been few and far between. Some towering cumulus have been noted on satellite imagery over the Big Island, where the afternoon 00z Hilo sounding indicated slightly higher CAPE when compared with the previous couple of afternoons. While the probability is low, isolated thunder has been introduced for the Big Island interior through the remainder of the afternoon. Meanwhile, surface observations and a late morning scatterometer pass show moderate trade winds prevailing across the state.
Guidance suggests that the trough aloft will pinch off into a cutoff upper low, located southwest of the islands by Thursday. As a result, more organized thunder potential and chances of heavy rain will shift far south/southwest of the state. For the islands, showers will favor windward and mauka areas, particularly in the overnight through morning periods. Isolated thunderstorms cannot be ruled out again on Wednesday afternoon for the Big Island, though increasing stability should mitigate these chances by Thursday.
Drier air begins to work into the area late in the week, with typical trade wind showers expected Friday into the first half of the weekend and light to moderate easterly trades.
An early November cold front may reach the northern coastal waters this weekend, with winds backing to become more northerly by Sunday. Beyond the weekend, there are significant differences amongst the various global models regarding the strength of an assoicated upper trough or potential low aloft. The development of this feature and its evolution would have significant impacts on the rain forecast and thunderstorm chances for early next week. For now, the forecast has been trended wetter to account for the possibility of a lower level trough/front hanging up north of the state, but have removed isolated thunderstorm chances in the extended forecast for now since it is too early to determine specifics based on the spread of model solutions at this time.

Aviation

Moderate trade wind regime continues with typical windward isolated showers over the islands becoming more scattered overnight.
Light icing impacts have decreased due to mostly clear conditions in the mid and upper levels.

Marine

Weak high pressure anchored north of the Hawaiian Islands will maintain moderate to locally fresh trades through the first half of the weekend. The potential then exists for trades to back to a more NEly direction and become strong over the western waters in the wake of a cold front that is forecast to advance through part or all of the island chain early next week. A Small Craft Advisory for winds and/or seas may be needed for portions of the area by early next week.
Energy out of the NW (330-350) remains small and rather short period through Friday. Surf will then trend sharply upward late Friday through through Monday in response to a couple of swells sent toward the islands by an active pattern across the N Pac. Forerunners of the first swell in the sequence, a small, moderate period NNW (330) swell are modeled to arrive on Friday with swell peaking Saturday below the High Surf Advisory (HSA) threshold. The next swell, small to moderate and medium period out of the NNW (340), arrives quickly on its heels late Saturday likely peaking above the HSA threshold. Messy forecast scenario during this time as modeling seems to contaminate this second swell with emerging strong NNE post-frontal winds leading to explicit output reflecting a larger and more N swell than anticipated. However, even a conservative approach suggests HSA-criteria surf for N and W facing shores for the Sunday-Monday period.
Surf along E shores remains small to moderate as trades slightly weaken. Strengthening post-frontal NNE trades potentially bring a rapid increase in wind waves and short period fresh swell for favored exposures early next week, particularly over the western end of the state. South facing shores see small background swells through the week.

Fire weather

Increased relative humidity values and moderate trade wind speeds will keep fire weather conditions below critical thresholds for the next several days.

HFO Watches/Warnings/Advisories

None.

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