Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 88 near the shore to around 75 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows around 73 near the shore to around 63 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 88 near the shore to around 75 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 80 to 88. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows around 75. East winds around 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 88. East winds 15 to 20 mph. Chance of rain 60 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Highs 73 to 84 in the valleys to around 65 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 65 to 71 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 84 in the valleys to around 64 above 4000 feet. East winds 15 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 76 to 89. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 67 to 74. East winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 88. East winds 10 to 15 mph. Chance of rain 60 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 72 to 86. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 67 to 77. East winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 85. East winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

An upper low will drift over the island chain through tonight. A highly moist resident air mass, along with the instability induced by the low, will likely result in widely scattered to numerous showers with the possibility of isolated thunderstorms. Showers may occasionally become heavy in intensity and create nuisance flooding issues. The statewide Flood Watch remains in effect through this afternoon. This unsettled weather pattern will likely linger and focus on more western islands into early Tuesday morning. A drier and more stable trade wind pattern will return by the close of business Tuesday.

Discussion

Early morning satellite imagery fixes the center of the upper low southwest of Big Island. 12Z soundings still verify a deeply moistened environment over us with near 2 inch precipitable waters registering well above seasonable norms for late October. This deep moisture, combined with the instability provided by the vicinity upper low, will continue to support moderate to high shower chances and isolated thunderstorms across widely-scattered statewide locations and surrounding coastal waters through early Tuesday. The overall theme of both the high resolution/global scale deterministic and ensemble guidance is that the bulk of the precipitation will fall within the next 24 hours while gradually transitioning toward the western half of the island chain, following the upper low as it slowly moves west southwest of the state through Tuesday morning. FWIW, the highest ensemble probabilities of the greatest rainfall (highest 24 hour QPF) focuses over the island of Kauai…with windward Big Island taking second place. The bulk of any thunderstorm activity should remain in the far south southwest offshore waters closer to the core of the low through the day although isolated thunder cannot be ruled out within outer convergence bands. NWP model blends focus the higher storm probs over the western waters or around Kauai late tonight into early Tuesday morning. The low is expected to fill in as the Central Pacific falls under the influence of upper ridging to the north by the middle of the week.
Easterly veering southeasterly winds could easily allow pockets of rain to become anchored along mauka slopes. This is where the highest probability of flooding concerns exist. Due to the widely scattered nature of the shower activity flaring up under such a broad large scale upper low, the greatest uncertainty lies in the 'when' and 'where' these cells may become anchored today. This lack of confidence amidst a proximity low within deep tropical moisture provides enough evidence to justify keeping the Flood Watch in effect through this afternoon. As ridging builds in and trades stay breezy the next few days, areas of the most intense rain will be concentrated along windward-exposed higher terrain. Wind sheltered leeward locations could also experience periods of moderate to heavy showers, particularly if early day cloud breaks allow more sun to warm the surface.
The Big Island summits experienced a some light snow accumulation early Sunday before quickly melting away with the rising sun. Current near freezing temperatures will have any pre-dawn precipitation falling as snow right along the summits. Snow accumulations should remain under couple of inches. Any mixed or liquid precipitation above 12k feet may freeze upon contact with colder surfaces and create some light icing issues.
This week's trades will be breezy as ridging builds in northeast of the state the next couple of days. This will reinstate a tighter upstream pressure gradient and restrengthen trades. As the upper low washes out southwest of the islands and surface ridging builds to the north Tuesday, a breezy and increasingly stable trade wind regime is expected through mid to late week. Pockets of higher mid-layer moisture riding in on trades will contribute to intermittent windward-exposed shower activity throughout the week. It appears the highest rainfall from a slug of passing mid layer moisture will likely drop the greatest areawide rainfall Thursday and/or Friday.

Aviation

Breezy easterly trades will continue, with clouds and showers favoring windward slopes and coasts. Some showers could become heavy at times due to added instability associated with an upper low moving through the area. AIRMET Sierra for mountain obscuration will persist through the early morning hours for windward slopes.
AIRMET Tango remains in effect for tempo moderate low-level turbulence downstream of island terrain below 8000 feet.

Marine

High pressure building far northeast of the islands will persist through the week, supporting moderate to locally strong trade winds. A Small Craft Advisory for waters around Maui County and the Big Island will likely remain in effect for the foreseeable future. An upper low near Maui County will drift slowly southwest, then west, over the next couple of days. Instability associated with the upper low will increase potential for locally heavy showers and/or thunderstorms through today, with the potential shifting westward with the upper low.
A small, medium-period north swell will persist through today, then gradually decline while another small north swell arrives on Tuesday. A small northwest swell is possible Thursday, with potential for a bigger, long-period northwest swell next weekend. A small long-period south swell will slowly decline through midweek. Surf will remain somewhat elevated along east facing shores over the next couple of days due to the combination of small long-period east swells generated by former major hurricane Kristy and increasing short-period wind waves as trade winds build.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov