Photo Credit: Jason Weingardt

West Kaua’i

Rest Of Today: Breezy. Partly sunny with scattered showers. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 66 near the shore to around 55 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Breezy. Scattered showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

South Kaua’i

Rest Of Today: Breezy. Partly sunny with scattered showers. Highs around 78. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Cloudy and breezy. Occasional showers in the evening, then numerous showers after midnight. Lows 62 to 67. Northeast winds 15 to 25 mph. Chance of rain 80 percent.

Tuesday: Cloudy and breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 78. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Rest Of Today: Mostly cloudy. Breezy. Occasional showers early in the morning, then numerous showers in the late morning and afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 90 percent.

Tonight: Breezy. Cloudy with occasional showers. Lows 55 to 60 in the valleys to around 49 above 4000 feet. East winds up to 25 mph. Chance of rain 90 percent.

Tuesday: Mostly cloudy. Breezy. Occasional showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds 10 to 25 mph. Chance of rain 90 percent.

North Kaua’i

Rest Of Today: Mostly cloudy. Breezy. Occasional showers early in the morning, then scattered showers in the late morning and afternoon. Highs 71 to 78. East winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Cloudy. Occasional showers in the evening, then occasional showers and isolated thunderstorms after midnight. Lows 58 to 67. East winds up to 15 mph. Chance of rain 90 percent.

Tuesday: Breezy. Cloudy with numerous showers and isolated thunderstorms in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 78. East winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Rest Of Today: Mostly cloudy. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Cloudy. Occasional showers in the evening, then occasional showers and isolated thunderstorms after midnight. Lows 56 to 68. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tuesday: Mostly cloudy. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

An upper level trough moving into the western half of the state, with higher moisture ahead of it, will continue to introduce periods of moderate to locally heavy rainfall that will primarily focused over Maui County and Big Island the next several days. Trade winds will remain the dominant wind pattern so expect the highest rainfall from passing showers to focus along windward areas.

Discussion

IR satellite depicts a jet streaming across the eastern half of the state this morning. A moist 1.8 inch pwat southern air mass advecting up within the jet has moistened the regional column to above 20,000 ft. The atmosphere is marginally unstable but, with the divergence brought on by this northeast-exiting jet within deep tropical moisture, the probability for isolated thunderstorm activity is alive but with a weak pulse. The higher probabilities reside in periods of moderate to locally heavy rainfall that, when anchored over more windward exposures, may produce rapid stream rises and runoff-induce flash flooding. Precipitation chances will be highest over windward Mauna Kea and Mauna Loa and Haleakala's slopes through the middle of the week. Rainfall amounts of between a half of an inch to an inch per hour will be common with localized greater than two inch hourly rates a more conservative, yet very plausible, occurrence each day through the week. A Flood Watch for Big Island and the island of Maui is in effect through the day. A large area of high pressure situated north of the state will produce a tight enough pressure gradient down across the state to result in several days of fresh to locally strong easterly trade winds. Easterly will strengthen through mid week and there is a possibility that winds could reach Wind Advisory criteria across higher elevation summits from Tuesday through late week.
A Winter Storm Warning remains is effect for the Big Island summits through this afternoon for frequent periods of snow and freezing rain. Temperatures at the summits of the Big Island should remain in the upper 20s to lower 30s, falling a bit more within periods of snow. Winds are generally light at the summits so, with the higher moisture moving in from the southwest within a sub-freezing air mass, these current conditions support the Winter Weather Warning through at least this afternoon.
High pressure to the northeast is moving away and will be replaced by a new high to the north of the islands through the day. This will result in strengthened trades from tonight into Tuesday. East trades will be breezy to locally windy for the remainder of the week. The upper level trough moving across the islands will maintain enough instability over the islands to warrant a higher possibility of periods of higher rainfall with isolated storms for primarily windward areas the next several days. The trough is expected to sink further south across the central islands Tuesday. This will assist in enhancing areawide trade wind showers for the remainder of the week.

Aviation

Moderate to breezy trade winds are forecast today as a high pressure system builds in north of the state. A low level trough moving westward across the islands with an upper level trough and subtropical jet stream will enhance shower activity for all islands favoring windward and mountain areas. Periods of MVFR conditions with low ceilings and visibility in showers are expected mainly over windward airfields through today. The eastern slopes of the Big Island will see more frequent MVFR conditions over the next 12 hours.
AIRMET Sierra remains in effect for mountain obscuration along windward slopes of Kauai, Oahu and Big Island due to clouds and showers. This AIRMET will decrease in coverage this morning.
AIRMET Tango is in effect for moderate leeward mountain wave turbulence over all islands due to breezy winds. This AIRMET will continue into Tuesday.

Marine

High pressure north of the state will remain nearly stationary before drifting east throughout the week keeping fresh to strong trade winds in place over the coastal waters. A Small Craft Advisory (SCA) is out for all waters through tonight due to a combination of winds and seas. The SCA will likely be extended through the week as the trade winds look to remain strong. An upper level trough moving through the islands from the west will keep the potential for instability and thunderstorms over the next few days.
North facing shores will remain elevated today as the moderate, medium to long period northwest swell has filled in before declining tonight and Tuesday. The dropping moderate medium period north swell will continue to decline today. Due to the swell height and direction, the Marine Weather Statement has been taken down for Maui and Big Island windward waters.
Choppy, moderate trade wind swell will remain in place throughout the next several days, keeping surf rough along east-facing shores. Surf along south facing shores will remain small this week with no significant south swells expected.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Big Island Summits, 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.
Winter Storm Warning until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian waters,

Data Courtesy of NOAA.gov