Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny with scattered showers. Highs around 88 near the shore to around 75 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

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

Friday: 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.

South Kaua’i

Today: Partly sunny with scattered showers. Highs 79 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

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

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 89. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with numerous showers. Highs 73 to 84 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 85 in the valleys to around 66 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with numerous showers. Highs 75 to 88. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 73. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 88. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy with numerous showers. Highs 72 to 85. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 73 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure far northeast of the islands will maintain a tight enough pressure gradient back toward the region and produce breezy to locally windy trade winds. Occasional periods of higher moisture moving in from the east this week will increase shower frequency and areal coverage. Higher rainfall will focus along windward-facing mauka the next several days. Trades will slightly back off this weekend but the wet pattern will likely persist.

Discussion

It appears our recent wet weather pattern has lined up with our climatology and verified that we are now entering our rainy season. This wet pattern will likely continue through early November as slugs of higher mid-level moisture, becoming deeper within the column, stream in from the east in tandem with a southwest-to- northeast orientated upper level trough axis laying over the western offshore waters. The majority of shower activity will focus along windward-exposed areas and higher terrain. This morning's satellite is evidence to the higher moisture as thicker, warmer clouds just upstream of the Hawaiian Islands advance in upon established trade winds. Enhanced mid-layer moisture will provide enough instability, with topographic lift, to generate periods of scattered to numerous showers across all of the islands in the foreseeable future. The main forecast challenge will be the timing of the heaviest rain and monitoring for potential flooding issues as rain falls on more saturated grounds and/or as cells anchor along higher terrain. Recent numerical weather prediction (NWP) guidance has aimed the greater early morning rain over where the moisture will first encounter windward Big Island/Maui slopes and just east of the western trough axis on Kauai. While there are low probabilities of locally heavy windward precipitation due to today's expected progressive cell movement, there should not be any statewide flooding issues with anticipated brief light to locally moderate intensity showers. It may be wise for those out tonight to have a quick (and drier) Plan B or take an umbrella to account for passing showers. This evening's forecast for most communities is moderate to low end high rain chances (25-50%), higher chances reside over windward Big Island (Hilo) and Kauai (Lihue).
There is little change in the medium to long term outlook where the latest guidance depicts an unwavering surface high north northeast of the islands maintaining breezy to locally windy trades through the remainder of the week. The upper level trough over the western islands will lift north through late week as another upper trough develops in its wake by early next week. The surface high far northeast of the islands will begin to move a bit east early next week and this will translate to a subtle decrease in slightly-veering trades. Intermittent showers may thin out a touch across the state as relatively drier air quickly advects across the island chain Saturday into Sunday. The 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 this trough's depth/strength. The two major determiners on whether we score our first frontal passage of the season in about a week will be trough depth and the southeasterly 'punch' of the backing high/upper ridge (i.e., mid-upper level temperatures, ridge orientation in relation to islands). The over is that 500 mb temperatures are progged to fall into the negative teens (deg C) over the northwestern offshore waters with a trough base swinging through south of 22N. The under 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 steering flow and washing out over the northern waters. Regardless of each individual model's upper support story, an early November (wet) signal is certainly becoming more evident. Thus, the early to middle part of next week is shaping up to be wet with safe bets leaning toward a blend of the NWP guidance.

Aviation

Moderate to locally breezy trades expected. A plume of low level moisture is moving up the island chain from the southeast bringing an uptick in low cigs and SHRA mostly over windward and mauka areas with isol spillover to leeward sides. MVFR/IFR conds are possible in any heavier SHRA. VFR should prevail elsewhere.
AIRMET Sierra is in effect for mtn obsc for windward portions of all islands.
AIRMET Tango is in effect for mod low level turb lee of island terrain and will likely stay in place over the next day or two.

Marine

Expect fresh to strong trade winds to continue through Friday, then decrease into the gentle to fresh range this weekend as the ridge north of the island chain weakens. The Small Craft Advisory was extended in time for the typical windier zones and waters around Maui and the Big Island through Friday afternoon.
A small north-northeast swell will lower into Friday. An upward trend is expected this weekend due to a storm force low centered over the western Bering Sea. Expect small, long period forerunners to arrive around by Friday afternoon from the north-northwest, then building over the weekend with peak swell heights arriving on Sunday. Surf heights could approach advisory levels for exposed north and west facing shores during the peak of the swell on Sunday, especially if the swell heights comes in higher than predicted.
Surf along east facing shores will remain rough through the week due to the strong trades locally and upstream across the eastern Pacific. A downward trend is forecast for 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 PM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov