Photo Credit: Jason Weingardt

West Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Highs around 83 near the shore to around 68 above 3000 feet. East winds up to 10 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows around 68 near the shore to around 58 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs around 85 near the shore to around 70 above 3000 feet. Light winds. Chance of rain 40 percent.

South Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Highs 75 to 82. East winds around 10 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows around 68. Northeast winds around 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 77 to 84. East winds around 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Cloudy with showers and isolated thunderstorms. Highs 70 to 80 in the valleys to around 60 above 4000 feet. East winds around 10 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 63 to 68 in the valleys to around 55 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 71 to 82 in the valleys to around 63 above 4000 feet. East winds around 10 mph. Chance of rain 40 percent.

North Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Highs 73 to 83. East winds around 10 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 62 to 71. East winds up to 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 75 to 85. East winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Today: Cloudy with showers and isolated thunderstorms. Highs 70 to 80. East winds around 10 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 62 to 71. Northeast winds around 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 72 to 82. East winds around 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

An unstable upper low slowly drifting eastward through the islands will continue to produce periods of heavy rain and thunderstorms with elevated flood threats statewide today. Weather conditions around this upper low will support some of these thunderstorm intensities becoming strong to severe. Heavy rain, flooding, frequent lightning and strong gusty winds will be the primary threats. By Monday the upper low weakens and lifts towards the northeast away from the island chain, decreasing the thunderstorm and heavy rain activity. However this wet weather pattern will likely continue through the week as another stronger low pressure system approaches from the north, possibly producing southerly kona winds over the western islands by Wednesday.

Discussion

The satellite water vapor channel imagery this morning continues to show an unstable cold core upper low over Maui County drifting slowly eastward. The orientation of this low will pivot over the islands as a secondary pulse of energy moves into Kauai and Oahu today extending the threat for heavy rain and thunderstorms over the western islands. This rather large and unstable upper low will produce periods of heavy rainfall and thunderstorms across the state into Sunday. Some of these thunderstorms will grow into the strong to severe intensity range. The main threats with this system will be heavy rain, flooding, frequent lightning, and strong gusty winds near thunderstorms. The Flood Watch was extended for all islands through this evening. This watch may decrease in coverage for the western islands by tonight.
In the short term, global model guidance shows the upper low pivoting over the islands today before slowly weakening and drifting northeastward away from the state. Enough instability and vertical wind shear will produce periods of isolated to scattered thunderstorms across the state. Some of these storms will become strong to severe in intensity with strong gusty winds, hail, and the potential for water spouts. Flash flooding, strong gusty winds and frequent lightning will develop quickly in this weather pattern and for these reasons outdoor activities this weekend should be postponed if possible.
Monday through Tuesday…Heavy rain and thunderstorm threats diminish by Monday as the low weakens and slowly drifts northeastward away from the state. Weak upper level troughing however will keep wet weather in the forecast with southeasterly winds over the islands through Tuesday.
Wednesday through Friday…Another unseasonably strong low will approach the islands from the north on Wednesday. A surface low forming under the upper low will be stronger than the previous system and may produce southerly kona winds over the western half of the state. The latest forecast guidance shows the surface low center will setup roughly 400 to 600 miles west-northwest of Kauai. This unstable southerly kona wind flow may bring another round of heavy rain and thunderstorms favoring the western islands of Niihau, Kauai and Oahu from Wednesday through Friday. In the latest model solutions Kauai County will be under the highest threat for flooding, thunderstorms, and strong gusty winds during this time period. This portion of the long range weather forecast will likely change over time. Much of these severe weather impacts are highly dependent upon the location of this low pressure system relative to each island. Small changes to the location of the low center will make large changes to the island forecast. Stay tuned for changes to the long range local weather forecast, as the time period grows shorter, and island by island weather impacts evolve.

Aviation

A strong upper level disturbance will continue to move across the state today. Enhanced shower activity and isolated to scattered thunderstorms will produce periods of MVFR and local IFR. Light winds should allow for sea breeze development this afternoon, with scattered showers possible over the interior and sheltered leeward areas.
AIRMET Sierra for tempo mountain obscuration remains in effect for the Big Island this morning. It may become necessary to include the smaller islands later today as shower activity increases.
AIRMET Tango for moderate to isolated severe mid to upper level turbulence remains in effect as the upper level disturbance moves across the state.
AMD NOT SKED for PMDY continues due to equipment issues, with no timeline for restoration.

Marine

Strong to severe thunderstorms are possible through today as an unusually strong upper level disturbance moves across the area. These thunderstorms have the potential to produce strong wind gusts, hail, and frequent lightning. Marine interests should continue to monitor for Special Marine Warnings that may be issued. Light and variable winds will prevail across local waters, except within and near thunderstorms. Light to moderate easterly trade winds will begin building back into the region on on Sunday.
A long-lived south swell will affect the islands this weekend. Although the swell will persist for the next several days, surf should continue to trend down as the period declines. Another series of overlapping, long-period south swells will give another sizable boost to south shore surf Wednesday through late next week.
A small, reinforcing short-period north-northwest swell will increase north and west shore surf through this morning, then decline later today into Sunday. A new small, long-period northwest swell will build Sunday night, giving north shore surf a boost early next week. Surf along east facing shores will be well below normal levels through the middle of next week.

HFO Watches/Warnings/Advisories

Flood Watch through this evening for all Hawaiian Islands.
Wind Advisory until 6 PM HST this evening for Big Island Summits.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.

Data Courtesy of NOAA.gov