Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with showers and slight chance of thunderstorms in the afternoon. Highs around 81 near the shore to around 69 above 3000 feet. Southeast winds 10 to 15 mph. Chance of rain 80 percent.

Tonight: Cloudy and breezy. Numerous showers and slight chance of thunderstorms in the evening, then numerous showers after midnight. Locally heavy rainfall possible. Lows around 70 near the shore to around 59 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Breezy. Cloudy with numerous showers. Highs around 82 near the shore to around 70 above 3000 feet. Southeast winds 15 to 20 mph. Chance of rain 60 percent.

South Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with numerous showers and slight chance of thunderstorms in the afternoon. Highs around 80. South winds up to 10 mph. Chance of rain 70 percent.

Tonight: Cloudy. Numerous showers and slight chance of thunderstorms in the evening, then numerous showers after midnight. Lows 66 to 71. South winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Cloudy with numerous showers. Highs around 81. Southeast winds 10 to 15 mph. Chance of rain 60 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers in the morning, then cloudy with showers and slight chance of thunderstorms in the afternoon. Highs 68 to 76 in the valleys to around 63 above 4000 feet. South winds around 10 mph becoming up to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy and breezy. Showers and slight chance of thunderstorms in the evening, then showers after midnight. Lows 59 to 64 in the valleys to around 53 above 4000 feet. South winds 10 to 20 mph. Chance of rain 90 percent.

Tuesday: Breezy. Cloudy with numerous showers. Highs 69 to 77 in the valleys to around 64 above 4000 feet. Southeast winds 10 to 20 mph. Chance of rain 60 percent.

North Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with showers and slight chance of thunderstorms in the afternoon. Highs 73 to 80. South winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 80 percent.

Tonight: Cloudy. Showers and slight chance of thunderstorms in the evening, then showers after midnight. Lows 62 to 71. Southeast winds up to 15 mph. Chance of rain 80 percent.

Tuesday: Cloudy with numerous showers. Highs 74 to 81. Southeast winds 10 to 15 mph. Chance of rain 60 percent.

East Kaua’i

Today: Partly sunny with scattered showers in the morning, then cloudy with numerous showers and slight chance of thunderstorms in the afternoon. Highs 73 to 80. South winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy. Showers and slight chance of thunderstorms in the evening, then showers after midnight. Lows 60 to 72. South winds 10 to 15 mph. Chance of rain 80 percent.

Tuesday: Cloudy with numerous showers. Highs 74 to 81. Southeast winds 10 to 15 mph. Chance of rain 60 percent.

Detailed Forecast

Synopsis

A developing low far northwest of the islands will move southward today, then shift west and away from the state thereafter. This low will shift our winds to southerlies and southeasterlies today, bringing deeper moisture over the western islands during the first half of the week. Breezy to windy trades and more typical weather should return for the second half of the week.

Discussion

Winds are veering to southeasterlies, as expected, as a developing low far northwest of the islands moves southward and adjusts the wind field this morning. Cloud cover across the smaller islands decreased dramatically overnight, with broken low clouds persisting across windward Big Island areas. Broken to overcast low clouds also persist across waters southwest of Maui County. Radar shows scattered showers within residual cloud areas. Winds will continue to veer through today.
Models shows the low will move to the south today, then move west away from the state afterwards. Confidence is high that the associated front will remain just west of Kauai, which should keep the main area of instability to the west as well. However, enough additional moisture and instability east of the front will reach Kauai to prompt the addition of thunderstorms to the forecast there from this afternoon into Tuesday. Spotty heavy rainfall is possible as far east as Oahu tonight into Tuesday.
Overnight soundings show a thermal inversion around 10,500 feet. We expect this inversion to remain in place for another day, but it may become weaker on Tuesday. As moisture increases near the Big Island Tuesday, we will look more closely at the possibility for thunderstorm development over the slopes, with the eruption helping to provide some of the instability needed. A transition back to a more typical trade wind pattern is expected to spread from east to west across the state late Tuesday night and Wednesday as a new high builds north of the islands.

Aviation

As a low develops far northwest of the islands, light to locally moderate winds will shift more to the southeast and south through today. Moisture moving up from the south and southwest will mainly affect the western part of the state, with Kauai and Oahu likely seeing the most lower cloudiness and showers, and accompanying MVFR conditions. And with lighter winds, afternoon sea breezes may also affect the isles, with convective buildups over leeward and interior sections.
No AIRMETs in effect.

Marine

Latest surface analysis and satellite imagery show a low that has developed roughly 475 nm NW of Kauai along a cold front and surface ridge to the north. This low will move SW today and develop into a storm- force kona low today. Gentle to fresh east to southeast winds will continue to veer out of the south today as these features approach the area today and strengthen to moderate to locally strong. Low- level convergent flow on the SE side of the low could prompt the development of heavy showers and possibly a thunderstorm over Kauai waters, later today and tomorrow.
The kona low is expected to move steadily W by tomorrow through the week, with high pressure strengthening to the N. The tightening low- level pressure gradient will support strong SE winds by tomorrow, backing to the E by Wednesday, and remaining strong to near-gale force through the end of the week. Winds and seas will likely increase to the point that a Small Craft Advisory (SCA) will be required for most (if not all) zones by tomorrow.
Mid- to short-period NE swell continues to be the primary wave energy early this morning according to near shore PacIOOS buoy data, as the ongoing WNW swell fades out. Some modest NE swell reinforcements are expected tonight, with this swell then gradually diminishing over the next several days. Surf along E facing shores will increase by midweek as trade winds increase near and upstream of the islands, and may lead to high surf. While most of the strong winds associated with the kona low will not be aimed directly at the islands, the proximity and strength of the low is expected to send NW swell toward the islands today and Tuesday, with the swell largest on the W end of the island chain. Offshore buoys have yet to pick up on this swell which is why it was decided to hold off on issuing an advisory with this package. Latest model guidance has also come in lower on the predicted peak surf heights, thus confidence in this swell peaking up to warning levels is still uncertain but not totally out of the question, especially for Kauai. After this swell peaks and diminishes, little in the way of NW swell is expected into next weekend.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov