Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 85 to 90 near the shore to around 75 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

South Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 80 to 88. East winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 84 in the valleys to around 65 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 83 in the valleys to around 65 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 88. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 73. East winds up to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 77 to 88. Southeast winds up to 10 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 86. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 72 to 86. East winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure far north northeast of the islands will maintain a tight pressure gradient back toward the islands. This will produce gentle to breezy trade winds through tonight. Occasional periods of higher moisture moving in from the east will promote higher shower frequency and areal coverage. Showers will ride in on the trades and primarily focus along windward mauka exposures. Trades will slightly back off this weekend with lessened shower activity. The approach of a cold front may initiate a more wet pattern next week.

Discussion

Statewide gentle to breezy early morning trade winds with slightly more shower coverage as we head into the sunrise hour. Most of the overnight rain fell across windward mauka, centered more on the islands of Oahu and Big Island where 12 hour rainfall accumulations of greater than 3 inches were recorded at the Honolii Stream and Saddle Quarry gauges. A 1030 mb surface high centered around 850 miles north northeast of the state remains the main driver to breezy conditions. Periodic rain episodes will be the ongoing theme going this first week of November. Rounds of higher mid-layer moisture trapped under a 7-8k ft trade inversion will stream in from the east today. This enhanced mid-layer moisture will provide enough instability, with topographic lift, to generate periods of scattered to numerous showers across all islands. Higher rainfall accumulations will occur over windward- facing slopes and within higher terrain where cells become more rooted within these stout easterlies. Today's main forecast challenge will again be timing the heaviest rain and monitoring for any potential flooding issues that arise if rain falls on more saturated grounds and/or as cells anchor within higher terrain. Recent numerical weather prediction (NWP) deterministic and ensemble QPF guidance continue to aim the greater short term rain over where higher moisture first encounters elevated land; likely windward Big Island slopes. While there are low probabilities of locally heavy windward precipitation due to progressive cell movement, there should not be any statewide flooding issues within anticipated brief light to locally moderate intensity showers.
Heading into the weekend, the high far north of the area will begin to drift east. This will result in a weakened pressure gradient back toward the islands. This will create a slight downtrend in the winds while veering more east-southeast. Mid- level ridging north of the islands will have more of an influence on weekend weather. Along with the stabilizing effect of this ridge, showers will become less frequent as relatively drier air advects across the island chain Saturday into Sunday.
There is little change in the medium to long term outlook where NWP guidance is steady in depicting an unwavering surface high north northeast of the state. This will guarantee breezy to locally windy trades through next week. Global models remain in decent agreement with the high to the northeast and a cold front /upper trough approaching the islands from the northwest but they differ on the trough's depth/strength. Moisture pooling up ahead of the approaching trough, as the state falls on the eastern convergent side of developing broad mid-level troughing, will increase Monday into Tuesday's rain chances…especially over the eastern half of the state. The two major determiners on whether we score our first frontal passage of the season at mid week will be the depth of the trough and the southeasterly push of the backing high/upper ridge (i.e., mid-upper level temperatures, ridge orientation in relation to islands). The pro argument is supported by decent 500 mb cooling into the negative low teens (deg C) over the northwestern offshore waters with a trough base swinging through south of 22N. The converse to that argument is that upper ridging may travel more east than southeast. The former has a slowing front reaching Kauai. The latter scenario translates to a weaker front becoming more parallel with the mid-upper steering flow and washing out across the northern waters. The possibility for winter weather (snow) on Big Island summits, along with increased thunderstorm coverage, may be in the discussion four or five days form now. Regardless of each individual model's upper support story, an early November (wet) signal is evident. The early to middle part of next week is shaping up to be more wet with the safer bet leaning toward a blend of the NWP guidance.

Aviation

Moderate to locally breezy trades continue today, with a downward trend and a shift more easterly expected tonight. A band of enhanced moisture will keep showery conditions in place over windward slopes and coasts early this morning, with conditions then improving statewide by mid to late morning.
AIRMET Sierra remains in effect for mountain obscuration over windward portions of Kauai, Oahu, Molokai, Maui and the Big Island. Conditions are expected to improve around mid to late morning.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of the terrain of all islands. This AIRMET will likely be needed through the day.

Marine

Fresh to strong easterly trade winds will continue today. Winds will then ease into the moderate to locally fresh range out of the east-southeast over the weekend and into early next week. An uptick in winds is expected towards the middle of next week as a front moves across the waters. A Small Craft Advisory remains in effect for the typical windier waters around Maui and the Big Island through tonight.
A small north-northeast swell will decrease this morning. An upward trend is expected this afternoon due to a storm force low centered over the western Bering Sea that showed a large swath of storm- force winds aimed at Hawaii within the 310-330 degree directional bands. Expect small, long period forerunners to arrive by this evening from the north-northwest, then build through the weekend with peak surf heights arriving by Sunday. Surf heights look to approach advisory levels for exposed north and west facing shores on Sunday. The northwest swell heights will gradually decrease on Monday and then hold through Tuesday.
Surf along east facing shores will remain rough today due to the strong trades locally and upstream across the eastern Pacific. A slight downward trend is expected this weekend.
Surf along south-facing shores will remain small, with mainly a mix of short period southeast and background long period south swell energy.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov