Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 85 to 90 near the shore to around 77 above 3000 feet. Light winds. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs 85 to 90 near the shore to around 75 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 82 to 89. Light winds becoming northeast 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Cloudy with numerous showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly cloudy with scattered showers. Highs 79 to 87. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Cloudy. Occasional showers and slight chance of thunderstorms in the morning, then occasional showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 75 to 83 in the valleys to around 68 above 4000 feet. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy and breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 64 to 72 in the valleys to around 60 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 80 percent.

Wednesday: Breezy. Mostly cloudy with numerous showers. Highs 72 to 82 in the valleys to around 64 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 70 percent.

North Kaua’i

Today: Cloudy. Occasional showers and slight chance of thunderstorms in the morning, then occasional showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 77 to 87. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy with numerous showers. Lows 66 to 73. East winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 88. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Cloudy. Occasional showers and slight chance of thunderstorms in the morning, then occasional showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 75 to 87. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy with numerous showers. Lows 66 to 76. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 84. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A surface trough and its associated plume of tropical moisture will maintain the potential for locally heavy rain and a few thunderstorms across portions of the state before it dissipates later today. A cold front will approach the islands and move part-way through the state on Wednesday into Thursday morning, then stall and dissipate as a new high builds to its north. This will bring a period of wet trades and breezy to locally windy conditions later this week and into the weekend, with clouds and showers favoring windward and mauka areas.

Discussion

Early morning satellite imagery and the latest surface analysis shows a nearly stationary trough across the Kauai Channel. CIMSS MIMIC precipitable water imagery continues to show a broad area of 2+ inches of precipitable water upstream of this trough. Short term guidance shows this trough remaining stationary today before dissipating by this evening. Guidance also continues to show a weak upper level trough moving across the region today which will help to increase instability across the state. The main concern continues to be the ongoing potential for heavy rain, with the threat shifting to Oahu and Kauai today. A Flood Watch remains in effect for Maui and the Big Island through this afternoon, but as the focus of the rain shifts westward it is likely that the watch gets cancelled earlier than expected. Brief periods of heavy rain remains possible across Oahu and Kauai today before the trough dissipates, but confidence is too low to expand the Flood Watch to these islands.
Radar and satellite imagery continue to show areas of deep convection associated with the trough. Heavy rain fell over the Big Island yesterday with rainfall rates up to 3 inches per hour. 24 hour rainfall totals over the Puna and Kau Districts ranged between 8 to 12+ inches. This lead to localized flash flooding with multiple road closures reported by Hawaii County Civil Defense. The threat of heavy rain is generally on the downswing across the Big Island as stream and river gauges continue to fall. Maui may see a brief period of heavy rain this morning, but the latest satellite and radar trends tend to keep the heaviest rain to the south, with localized heavy shower bands briefly moving into the eastern part of the islands near Hana.
Moderate to locally breezy trades will weaken slight today as a cold front approaches from the northwest. This front is expected to arrive by Wednesday. Both the ECMWF and the GFS have this front move down to somewhere near Maui County or the Big Island Wednesday evening into Thursday morning. Showers are expected along and ahead of this front due to the lingering tropical moisture. The surface high pushing in behind the front will lead to a resurgence in the trades, with breezy to locally windy conditions developing by late Wednesday and holding into the weekend. Moisture caught up in these trades will bring periods of enhanced showers to mainly windward and mauka areas.
Models begin to diverge more significantly this weekend heading into early next week. For now, have kept a wet breezy to strong trade wind pattern through the end of the forecast period.

Aviation

Moderate to locally breezy trades will weakens slightly through the period. A surface trough will stall near Kauai and Oahu today. Low cigs and heavy SHRA and some isol TSTMs associated with the aforementioned trough should continue moving across the island chain. MVFR/IFR conds can be expected in heavier SHRA/TSTMs across the east end of the state and in any SHRA over windward and mauka portions of the west end of the state. These low cigs and SHRA should spread to Oahu and Kauai mid morning into the afternoon.
AIRMET Sierra for mtn obsc over windward portions of all islands is in effect. Expect reduced vsbys and low cigs as previously mentioned.
AIRMET Zulu is in effect over and around the Big Island for light ice from 140 to FL270. This may be carried to other islands as conds warrant as the trough moves
AIRMET Tango is not in effect. Turb should only be significant in or around the heaviest SHRA/TSTMs, and at this time there is not enough coverage to warrant an AIRMET or even a SIGMET.

Marine

Moderate to fresh east-southeast winds will continue today before shifting to a northeasterly direction and strengthening tonight into midweek, as a cold front moves into the area. This pattern is expected to hold through the latter part of the week as high pressure builds to the north, and the front stalls and weakens in the area. Seas will rise to Small Craft Advisory levels, reaching around 10 feet by Thursday due to a combination of strong local winds and incoming north to north-northwest swells.
Surf along north and west-facing shores will lower through midweek as the large north-northwest swell that peaked on Sunday fades. However, conditions will trend up again starting Wednesday night through the weekend, with overlapping medium-period north to north-northwest swells expected due to an active pattern evolving over the northern Pacific. This, combined with strong northeast winds, will create rough conditions for most north- facing shores beginning Wednesday.
For the long-term (next week), the active pattern continues, with back-to-back gale- to storm-force lows racing eastward from the Kuril Islands to the Date Line Thursday through the weekend. This will generate two long-period northwest swells, with the first arriving Sunday night into Monday and the second around midweek. The first swell could generate near advisory-level surf along exposed north and west-facing shores by Monday night, with the second potentially generating surf closer to warning levels Wednesday.
Surf along east-facing shores will become rough starting Wednesday, with short-period and choppy conditions due to a combination of northerly swell and northeast wind-driven waves.
Surf along south-facing shores will remain near the seasonal average, with only small, short-period southeast swells and background long-period southerly swells expected through the week.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, 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.

Data Courtesy of NOAA.gov