Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 79 near the shore to around 67 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 66 near the shore to around 55 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 79 near the shore to around 67 above 3000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs around 78. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 67. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly cloudy with numerous showers. Highs around 78. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Occasional showers in the morning, then numerous showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Tonight: Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 55 to 60 in the valleys to around 49 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Monday: Breezy. Frequent showers. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

North Kaua’i

Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then occasional showers after midnight. Lows 58 to 67. East winds 10 to 20 mph. Chance of rain 90 percent.

Monday: Breezy. Frequent showers in the morning, then numerous showers in the afternoon. Highs 71 to 78. East winds 10 to 20 mph. Chance of rain near 100 percent.

East Kaua’i

Today: Mostly cloudy with scattered showers. Highs 71 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 56 to 68. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Breezy. Frequent showers in the morning, then numerous showers in the afternoon. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

A low level trough moving into the Hawaiian Islands from the east will combine forces with a developing upper low over the region and produce wet weather conditions across the state lasting into the middle of the week. The highest rainfall coverage will favor windward and mountain areas. Trade winds will continue to blow in the moderate to locally windy range into next week. A new high is forecast to build north of the islands on Tuesday increasing trade wind speeds up to the locally windy range.

Discussion

Satellite imagery this morning continues to show a rather interesting weather pattern developing over the next few days that will bring wet weather to all Hawaiian Islands lasting into the middle of this week. First, a low level trough shows up on infra- red satellite imagery moving into the islands from the east. This low level trough will combine forces with a deepening upper level trough and a subtropical jet stream shown over the Hawaii region on satellite water vapor imagery. Local radar imagery shows shower activity picking up along all windward slopes this morning as the low level trough slowly moves into the islands. The upper air balloon sounding from Hilo shows a more unstable atmosphere with temperature inversion heights rising to around 10,000 feet above sea level. A very wet weather trend indeed.
This complex weather pattern with both low level and upper level forcing may bring several inches of rainfall to the windward slopes of Maui and the Big Island from this evening through early Tuesday morning. Windward and mountain slopes of all islands will also see enhanced rainfall totals during this wet weather time period with higher rainfall coverage favoring the overnight hours. Isolated thunderstorms are also a good possibility as this trough moves slowly from east to west through the island chain.
Ensemble weather model forecasts from the National Blended Model, the European and American (GFS) ensembles are continuing to show the highest rainfall totals falling along the eastern slopes of the Big Island from the North Kohala area, down along the Hamakua Coast, into the Hilo and Puna Districts. Rainfall activity will continue to trend higher for the Big Island through the day today with more consistently heavier showers expected by this evening. Using the 90 percent ensemble threshold we see storm total amounts in the 4 to 8 inch range for these eastern Big Island slopes over a 36 hour time period. A Flood Watch for the Big Island was issued this morning to cover this increasing flood threat.
Trade winds will continue to blow at moderate to locally windy levels through much of the week. A high pressure system currently northeast of Hawaii will slowly drift towards the southeast and a cold front passing north of the island chain produces a slight weakening in the trade wind speeds today. Trade wind speeds pick up to breezy levels by Monday, then increasing to locally windy levels from Tuesday through Thursday, as yet another high center will build in north of the state. No end in sight to this trade wind weather with passing showers forecast from the middle to end of the week. Most of the shower activity will favor windward and mountain areas during the overnight to early morning hours.

Aviation

Moderate to breezy trades will persist through tonight and then strengthen heading into Monday. Clouds and showers caught up in this flow will bring periods of MVFR conditions to windward areas through the forecast period. An upper level trough moving in from the west with the subtropical jet will help to enhance shower development, especially near the Big Island as a plume of moisture moves in from the east later today…bringing more persistent MVFR conditions or lower for that end of the state.
AIRMET Sierra is in effect for tempo mountain obscuration along windward slopes due to clouds and showers. This AIRMET will likely be needed through today and into tonight for at least portions of the area.
AIRMET Tango is in effect for moderate leeward mountain wave turbulence over all islands due to breezy winds. This AIRMET will likely be needed through today. The subtropical jet will also bring the potential for moderate high level turbulence over and to the north and east of the state later today.

Marine

Generally moderate trade winds, locally strong over those waters surrounding Maui County and south of Big Island, continue across the nearshore waters. There has been a subtle decrease in overall wind speeds as high pressure centered approximately 700 nautical miles northeast of Oahu settles more southeast. The high will still maintain a tight enough pressure gradient across the coastal waters to warrant a Small Craft Advisory (SCA) for those windier Maui County and Big Island marine zones through this morning. A slight boost in wind speeds around Kauai, along with an incoming northwest swell that will pick combined seas up, the SCA has been expanded to include the Kauai waters including the Kauai Channel this afternoon…then windward Oahu and Maui waters including the Kaiwi Channel this evening. More areawide fresh trades will return by Tuesday morning as a new high fills into the wake of the aforementioned southeastern-exiting high. An approaching upper level trough out west, with a northeast-exiting jet stream ahead of it, in the vicinity of the eastern waters tonight through Monday morning will increase the thunderstorm threat across Big Island's windward coastal waters.
A moderate size, medium period north (010 degree) swell moving through the islands is forecast to peak through the day. North- facing harbors, particularly Kahului and Hilo Harbors, may experience minor surges from this incoming north swell through the day. A similar size moderate, medium to long period northwest (310 degree) swell will be arriving in Kauai's nearshore waters early this morning and reach Maui during the early afternoon hours. This swell will likely increase north and west-facing shore surf heights to near High Surf Advisory levels at its peak tonight into early Monday. Choppy, moderate trade wind swell may slightly decline today before rebuilding early this week and maintaining a rough chop along east-facing shores for several days. No significant south swell expected this week and will result in very small south-facing shore surf.

HFO Watches/Warnings/Advisories

Flood Watch from this evening through late Monday night for Big Island,
Small Craft Advisory from 2 PM this afternoon to 6 AM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.
Small Craft Advisory from 8 PM this evening to 6 AM HST Monday for Kaiwi Channel, Maui County Windward Waters.
Small Craft Advisory until 6 AM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov