Photo Credit: Brendan Stephen

West Kaua’i

Today: Cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 83 near the shore to around 73 above 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 66 to 71 near the shore to around 57 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 83 near the shore to around 73 above 3000 feet. East winds 10 to 15 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 81. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows 64 to 70. Northeast winds around 10 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs around 81. Northeast winds around 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Cloudy. Scattered showers and slight chance of thunderstorms early in the morning, then numerous showers and slight chance of thunderstorms in the late morning and afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows around 60 in the valleys to around 52 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs around 76 in the valleys to around 65 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 76 to 82. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows 60 to 69. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 76 to 82. East winds 10 to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 74 to 80. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Cloudy with numerous showers and slight chance of thunderstorms. Lows 58 to 71. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs 74 to 80. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Update

Just sent out a quick update to morning forecast to reflect increasing showers filling in over Oahu. For the moment, the remainder of the morning forecast appears to be on track.

Synopsis

Cloudy skies with numerous showers and isolated thunderstorms are possible in the vicinity of Kauai this morning. Instability due to an upper-level disturbance developing over the area combined with abundant moisture will likely cause increasing showers, along with a chance of thunderstorms across the entire state from this afternoon through early Monday morning. The trade winds will continue to become reestablished across the island chain through tonight, with locally breezy trades expected from Monday into mid- week. A relatively wet trade wind weather pattern will likely develop from Monday through Tuesday, with a slight chance of thunderstorms over portions of the Big Island each afternoon.

Prev discussion

/ISSUED 359 AM HST Sun Apr 2 2023/
A weak surface trough about 300 miles west-northwest of Kauai continues to move slowly westward away from the area. In addition, a 1033 mb surface high pressure system is cantered more 1800 miles north-northeast of Honolulu. The departing surface trough is allowing the pressure gradient to gradually tighten, especially over the eastern end of the island chain. As a result, the trade winds are gradually becoming reestablished in the vicinity of Maui and the Big Island.
Satellite imagery shows overcast high clouds across the western half of the state, with a mix of broken cirrus clouds and scattered to broken low clouds elsewhere. A mid-level trough approaching the state from the west is causing these high clouds to stream into the region. There is abundant moisture in the vicinity of the state, so there are scattered showers developing over the Kauai Channel just west of Oahu. Scattered trade showers are also streaming into windward Maui and the Big Island.
The forecast guidance indicates atmospheric instability will increase through today as the mid-level trough arrives. In the near-term, this may trigger a few thunderstorms near Kauai. The low-level trade wind flow will continue to bring showers to windward slopes of Maui County and the Big Island. A low is expected to develop aloft in the vicinity of the state later today once the mid-level trough arrives. This will likely provide a chance of thunderstorms from this afternoon through tonight. At the same time, the trade winds will continue to strengthen as the surface trough moves away, and the surface high pressure system builds as it pushes toward the south-southeast. This will bring low clouds and numerous showers into the windward slopes of most of the islands. The relatively unstable atmospheric conditions and deep moisture will also likely allow the showers to penetrate over some leeward sections.
The trades are forecast to gradually strengthen, with locally breezy conditions from Monday into mid-week. During this time, the low aloft in the vicinity of the islands is expected to migrate southwest of the area. As this occurs, conditions will be favorable for increased mid-level instability to wrap around the low, which could provide increased fuel for deeper convection and thunderstorms over, and in the vicinity of the Big Island on Monday and Tuesday, especially during the afternoon. There is a possibility that extensive high cloud cover may decrease the daytime heating over the Big Island, so this may be the main mitigating factor for a heavy rain threat to materialize over the Big Island interior on Monday and/or Tuesday. As the low aloft shifts south and west of the islands, a weak mid-level ridge may move over the area. This will result in increasing stability, which may mean a return to a more typical trade wind weather pattern during the second half of the new week.

Aviation

Mostly cloudy conditions with localized heavy showers and a few thunderstorms will remain in the forecast today as an upper disturbance and surface trough linger nearby. The low-level flow will remain out of the east-southeast this morning, then gradually shift out of the east and increase later today through tonight. Shower activity will favor the adjacent coastal waters and coasts this morning with the land breezes in place, then shift to windward locations as the winds become easterly.
AIRMET Sierra currently in effect for mountain obscuration over Kauai due to clouds and showers may need to be expanded eastward through the day as conditions evolve.
AIRMET Tango remains in effect for tempo moderate upper-level turbulence across the islands. This may hold through the morning hours, but guidance suggests this threat will decrease through the day. Light icing has been included to account for considerable mid- to high-cloud cover streaming over the state.

Marine

Some changes to the forecast this morning, but the overall flavor remains the same. Trades returning, with an unstable airmass over the region today, and no significant swells for the week.
A surface trough to the west of the islands will move to the west, allowing high pressure to the northeast of the islands to build back in. This will allow more easterly trade winds to build back in across the state, from south to north. Some areas will see a southerly component to the winds today, but expect easterly winds to build back later today and tonight. The current Small Craft Advisory (SCA) remains in effect for most of the coastal waters near Maui and the Big Island through tonight. Heading into tonight, in anticipation with the easterly winds spreading across the southern half of the area, the SCA will be in effect for the typical windier waters near Maui County and the Big Island. Some additional areas may need to be added, and the SCA will likely be extended through a good chunk of the week.
Meanwhile, an upper level trough to the northwest of the islands will continue to provide instability to spark some thunderstorm activity. The forecast this morning keeps that possibility focused on the waters near Kauai, but spreads the possibility to all waters by this afternoon and for tonight. The offshore wasters will have a chance for thunderstorms into the middle of the week with the main focus today being over the northwestern half of the offshore waters. That area will shift to the western and then southern waters over the next couple of days.
No significant swells are expected this week. The current northwest swell (320 degree) will continue to subside and becoming a background swell during the first half of the week. A small bump on the northwest is possible Monday, with a slightly larger bump possible midweek. Neither of these impulses will result in surf of any significance. As the high pressure mentioned above strengthens, the upstream trade winds swell will produce choppy surf conditions along east facing shores through the week. Small background energy from different southerly directions will continue small surf along south facing shores.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maui County Windward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov