Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Haze. Highs around 82 near the shore to around 70 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 67 to 72 near the shore to around 60 above 3000 feet. South winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 81 near the shore to around 71 above 3000 feet. South winds up to 10 mph. Chance of rain 70 percent.

South Kaua’i

Today: Mostly cloudy with scattered showers. Haze. Highs 78 to 83. South winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 68. South winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 81. Southwest winds around 10 mph. Chance of rain 60 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with scattered showers. Haze. Highs 73 to 80 in the valleys to around 63 above 4000 feet. South winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 67 in the valleys to around 58 above 4000 feet. South winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 40 percent.

Saturday: Cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 79 in the valleys to around 65 above 4000 feet. Southwest winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers. Haze. Highs 73 to 82. South winds up to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 70. South winds up to 20 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 81. South winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Haze. Highs 72 to 82. South winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 72. South winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 73 to 82. Southwest winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Showers will increase across western portions of the state today, but remaining limited over the rest of the islands. A cold front approaching from the northwest will maintain unsettled weather through the first half of the weekend, especially over the western portions of the state. The atmosphere will trend more stable on Sunday and Monday as trade winds return. Another front will approach the area from the northwest by the middle of next week.

Discussion

Radar this morning shows limited showers across the islands, with the most persistent showers lingering around Kauai and extending northeastward. The latest lightning data shows thunderstorms around 240 miles north through northeast of Kauai, in an area of modest instability (Showalter Index values around 0 to -2c). Otherwise radar and satellite show fairly limited showers and clouds across the rest of the smaller islands and Big Island.
This morning…the best chance for showers will remain across the western end of the state near Kauai. However, expect showers to remain limited in areal coverage across the rest of the islands, as the surface trough north of Kauai weakens and lifts northeast. Any thunderstorms are expected to remain well northeast of Kauai.
This afternoon through Saturday…A more robust cold front from the northwest will approach Kauai by Saturday afternoon. Current trends show this front stalling over the western end of the state Saturday night, before weakening and lifting northeast Sunday. Moisture lifting up across the region in advance of the front, will increase rainfall chances once again across Kauai this afternoon and expanding eastward to Oahu tonight. Some of the latest high- res model data shows showers increasing this afternoon across Kauai and later tonight/early Saturday across Oahu as the front nears. Have updated the near-term forecast to reflex an increase in shower chances over the western end of the state, as the latest satellite data shows an area of moisture beginning to pool south and southeast of the state already this morning. Model data shows some instability lingering across the state through Saturday evening, with Moisture Stability Index (MSI) between 1.5 and 2.5 (highest over the western islands), enough to generate some locally heavy rainfall with any showers that develop. Thunderstorm probabilities remain limited through the weekend. Shower chances will decrease across the entire island chain Saturday night, as the front weakens and exits northeast.
Sunday through next week…MSI values (less than 2) show a more stable pattern redeveloping over the state Sunday through Tuesday. A trade wind weather pattern becomes reestablished across the region Sunday into early next week, with trades focusing showers to mainly windward areas. Another cold front, with an assoicated band of moisture and increasing instability, and upper level trough will advance over the western end of the state by Wednesday. The front and band of showers will then potentially drift eastward across the remainder of the state through Thursday. MSI values increasing to between 2.5 and 3.5 suggest modest instability returning in advance of the approaching boundary. This pattern could reintroduce a chance for thunderstorms and potentially locally heavy rainfall once again next week.

Aviation

Early this morning, land breezes have diminished cloud cover over much of the islands, though some scattered clouds between 1,500 and 3,000 feet are observed across small portions of Oahu, Molokai, and Maui. An approaching front from the northwest will increase the pressure gradient across the state today, resulting in an uptick in southerly winds. Convergent southerly flow ahead of the front will lead to higher rainfall chances today and tonight near the western end of the state. The eastern islands will remain drier with VFR flight conditions prevailing.
AIRMET Tango has been issued for moderate upper level turbulence near Kauai early this morning as an upper jet approaches the area from the west. This AIRMET is likely to remain in effect through the next 24 hours and may need to be expanded to other islands by this evening. Additionally, AIRMET Sierra for tempo mountain obscuration may be needed later today or tonight for Kauai as the surface front approaches and increases low clouds and showers.

Marine

A front will approach the area today and dissipate over the northern offshore waters over the weekend, maintaining a slight chance of thunderstorms in the northern offshore waters into the weekend. Gentle to locally fresh east to southeast winds will veer slightly out of the south today and strengthen to moderate to locally strong ahead of the approaching front through Saturday. Gentle to moderate trades may return Sunday and gradually strengthen to moderate to locally strong through early next week as the front dissipates and a new high builds north of the islands. Winds and seas are forecast to remain below Small Craft Advisory (SCA) thresholds through at least Saturday.
A northwest swell will boost surf heights to advisory threshold across exposed north and west facing shores today and tonight. A High Surf Advisory remains in effect for exposed north and west facing shores through tonight. This swell will dip below advisory levels Saturday. A dangerous, extra large, long period northwest swell is expected to rapidly fill in Saturday night, peak Sunday, then slowly decline Monday through mid-week next week. Surf heights will be well above warning thresholds and may produce giant surf, over 40 feet during the peak of the swell along north facing exposures and near 30 feet or west facing exposures of the smaller islands. Rising seas due to this swell will likely meet SCA criteria Saturday night. In addition, the combination of rising surf and high tides from the new moon during the very early morning hours Saturday and Sunday will likely impact coastal properties and infrastructure, including roadways near the shorelines.
Background south swell energy is expected through Saturday. A new small long-period south swell could give south shore surf a minor boost Sunday through early next week. Surf along east facing shores will remain small due to the lack of trade winds over and upstream of the islands, but will gradually pick up Sunday into early next week as trades return and we may see another boost due to wrap from the extra large northwest swell.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.

Data Courtesy of NOAA.gov