Photo Credit: Braden Jarvis

West Kaua’i

Today: Breezy. Cloudy with scattered showers and isolated thunderstorms. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 15 mph increasing to up to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Cloudy with scattered showers and isolated thunderstorms. Lows around 68 near the shore to around 57 above 3000 feet. East winds 10 to 25 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Cloudy with scattered showers and isolated thunderstorms. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 15 mph becoming around 10 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Cloudy with numerous showers and isolated thunderstorms. Highs around 78. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Lows 64 to 69. Northeast winds 10 to 25 mph. Chance of rain 90 percent.

Saturday: Cloudy with showers and isolated thunderstorms. Highs around 78. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Kaua’i Mountains

Today: Breezy. Cloudy with showers and isolated thunderstorms. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Saturday: Showers and isolated thunderstorms. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

North Kaua’i

Today: Breezy. Cloudy with showers and isolated thunderstorms. Highs 71 to 78. Northeast winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Lows 60 to 69. East winds 10 to 25 mph decreasing to 10 to 15 mph after midnight. Chance of rain near 100 percent.

Saturday: Cloudy with showers and isolated thunderstorms. Highs 71 to 78. East winds 10 to 15 mph. Chance of rain 90 percent.

East Kaua’i

Today: Breezy. Cloudy with showers and isolated thunderstorms. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Showers and isolated thunderstorms. Lows 58 to 70. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Saturday: Showers and isolated thunderstorms. Highs 71 to 78. East winds 10 to 15 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

The remnants of an old cold front are drifting into the islands from the north this morning with a cut off low moving in from the west. These two low pressure systems will produce increasing shower activity over the islands of Kauai, Niihau and Oahu today and the eastern islands later tonight. A high pressure center passing north of the islands today will also bring a return to moderate to breezy trade winds lasting through the weekend. The upper level low will slowly move from west to east across the state this weekend spreading unstable wet weather to all islands, with heavy rain at times, and a few thunderstorms. More typical trade winds will return from Monday onward with passing showers as more stable conditions are forecast over the region.

Discussion

The weather pattern this morning shows a convergent cloud boundary associated with the remnants of an old cold front drifting into Kauai and Oahu. This surface boundary will combine forces with an unstable upper level cut off low drifting eastward into the western islands this morning. The combination of upper level and surface forcing from these two low pressure systems will increase shower activity over the western islands today with a few thunderstorms added to the mix. Trade winds are also expected to strengthen today over the western half of the state, then increasing over the eastern islands later tonight. These stronger trade winds will focus cloud and shower development over windward and mountain slopes of Kauai and Oahu today. The highest rainfall amounts are expected to fall along the windward and mountain slopes through today. However, thunderstorms also elevate the heavy rain potential even over leeward slopes. The potential for showers training over windward mountains elevates the flood threat, however we do not yet have high enough confidence to issue a flood watch product as of this morning's forecast package.
These wet weather conditions have already started over the western islands of Kauai and Oahu this morning, increasing showers will spread eastward across the rest of the island chain later tonight. The most unstable conditions with periods of heavy showers and thunderstorms move into Kauai County and Oahu from through Saturday. The eastern islands in Maui and Hawaii Counties will also see periods of rainfall, heavy at times with thunderstorms from Saturday into Sunday. The western islands, Kauai County and Oahu, will see decreasing rainfall trends on Sunday, as the upper low weakens and passes into the eastern half of the state. Stay tuned for forecast updates as this wet weather pattern and heavy rainfall threats evolve.
A more typical trade wind weather pattern with passing windward and mountain showers and moderate to breezy trades will return late Sunday for the western islands and by Monday over the rest of the state. A high pressure ridge will build in over the region keeping shower activity more limited to windward and mountain areas, especially in the overnight to early morning hours.

Aviation

Early this morning, showers and low clouds have increased from Kauai to Oahu in the vicinity of a trough near the western end of the state. A low aloft west of the islands will move over the state today through the weekend, increasing the potential for thunderstorms and heavy rain, especially over windward locations. MVFR ceilings can be expected for portions of Kauai and Oahu throughout the day today with wet weather remaining in the forecast and spreading further east to the remaining islands by tonight. Isolated IFR conditions will be possible within heavier showers or any thunderstorms that develop.
Based on latest observations and trends, AIRMET Sierra for tempo mountain obscuration above 1,500 feet has been updated to include Oahu as well as Kauai. This AIRMET will likely remain in effect through the day. AIRMET Tango for moderate mid and upper level turbulence remains in effect across the islands as well, though this will likely be cancelled later this morning as upper dynamics gradually weaken. However, as trade winds increase today through tonight, an AIRMET Tango for moderate low level turbulence will likely be needed.

Marine

A front will pass to our north and high pressure will build behind it today through the weekend. Fresh to strong northeast winds will accompany the tail-end of the front as it settles southward into the area later today. Winds will become easterly Saturday. Expect this pattern to hold through early next week as high pressure sets up north of the islands. Small Craft Advisory conditions due to strong winds are anticipated beginning this morning for some waters and these conditions may expand to other areas tonight and over the weekend. Seas will respond and may approach the 10 ft advisory threshold for exposed waters (windward waters) through the weekend.
Surf along north facing shores will slowly decline into the weekend. A medium-period north-northwest swell will arrive by the end of the day Saturday, then hold into Sunday before fading. On Monday, an upward trend is expected out of the northwest. This long-period northwest swell will slowly fill in through the day Monday, then peak sometime between Tuesday and Wednesday before lowering into the latter half of next week. If this materializes, surf could near advisory levels for exposed north and west facing shores of the smaller islands as it peaks. Surf along south facing shores will ease into the weekend as a long-period south swell moves through. Surf along east facing shores will trend up this weekend through next week as high pressure sets up to the north and a belt of fresh to strong easterly trades develops over and far upstream of the islands.

HFO Watches/Warnings/Advisories

Small Craft Advisory from 6 AM this morning to 6 AM HST Sunday for Kauai Northwest Waters, Kauai Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

Data Courtesy of NOAA.gov