Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly cloudy with numerous showers. Highs around 86 near the shore to around 71 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 69 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 71 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy with numerous showers. Highs 78 to 84. East winds around 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 69. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 85. Southeast winds up to 10 mph. Chance of rain 30 percent.

Kaua’i Mountains

Today: Occasional showers. Highs 73 to 82 in the valleys to around 64 above 4000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Cloudy with numerous showers in the evening, then partly cloudy after midnight. Lows around 67 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 70 percent.

Tuesday: Partly sunny with scattered showers. Highs 72 to 82 in the valleys to around 64 above 4000 feet. South winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 85. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 72. Southeast winds up to 10 mph. Chance of rain 60 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 84. Light winds. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy with numerous showers. Highs 73 to 83. East winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers in the evening, then partly cloudy with isolated showers after midnight. Lows 64 to 73. Light winds. Chance of rain 70 percent.

Tuesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 84. South winds up to 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Light southeasterly winds, afternoon sea breezes and weak troughing aloft will produce brief periods of slow moving showers over some islands through Tuesday. Some of these showers may become heavy at times especially along the eastern slopes of Oahu and Maui, and the southeastern slopes of the Big Island. On Wednesday the weather pattern trends more unstable as southerly winds develop over the state in response to a kona low approaching the islands from the north. Deep unstable tropical moisture will move over all islands from the south, resulting in periods of heavy rainfall, thunderstorms and strong gusty winds. The threats from flooding and thunderstorms will be elevated for all islands from Wednesday into the weekend.

Discussion

Local radar imagery this morning shows moderate showers anchored over the Koolau Mountains on Oahu from a Molokai convergence plume caught up in the light southeasterly winds. Showers over the eastern mountain slopes of Oahu will continue at least through the morning hours. Satellite imagery using the water vapor channel continues to show the weak upper low drifting northeastward away from the Hawaiian Islands today. Upper air balloon soundings from Hilo and Lihue show very weak to non-existent subsidence inversion. This means periods of wet weather should be expected today statewide. The forecast grids were updated significantly this morning in the medium to long range forecast to include higher chances for showers and thunderstorms from Wednesday on into the weekend.
The weather pattern for the next few days keeps the Hawaiian Islands in a light southeasterly wind pattern with land and sea breezes forming over each island through Tuesday. Forecast guidance and satellite water vapor imagery continues to show weak upper level troughing that will enhance some shower activity across the state. Southeasterly winds tend to produce small scale convergence plumes in the lee of island mountains and when combined with upper level instability tend to create enhanced showers over eastern Oahu. Southeasterly flow will also combine with sea breezes to drive clouds and low moving moderate to heavy showers up the mountain slopes of east Maui and the southeast slopes of the Big Island over the Kau and Puna districts. Localized slow moving heavy rain may also develop and Flood Advisories may be needed mainly in the afternoon to early evening hours through Tuesday.
Wednesday through Friday…Another unstable weather pattern develops across the Hawaiian Islands as a unseasonably deep kona low approaches the islands from the north. A cold front riding in ahead of this system will help to produce southerly kona winds over the islands starting early Wednesday morning. These southerly winds will draw up a deep and unstable tropical moisture plume ahead of the approaching cold front. The cold front will weaken into a trough on Thursday as it merges with the tropical moisture plume right over the islands. Forecast models have been remarkably consistent in showing both features will impact all islands with heavy rain and thunderstorm threats during this time period.
Several threats are likely in this weather pattern from Wednesday onward including heavy rain with flooding, thunderstorms in the strong to severe range, and strong gusty winds. The severe thunderstorm threat will favor the western islands closer to the approaching surface front/trough, the upper level cold pool and the strongest wind shear. The forecast guidance over the past few days suggests these threats will last for several days from Wednesday through Friday and possibly linger into next weekend. A very wet and unstable pattern for this time of year. Stay tuned.

Aviation

Lingering instability aloft combined with a moist southeasterly flow will allow for a few heavy showers across the state through the forecast period, with the slight possibility remaining for isolated thunderstorms over the Big Island today. The heaviest showers will mostly be focusing over southeast facing slopes of each island. Winds will remain light enough to allow for a land/sea breeze pattern where clouds and showers will build up over island interiors during the afternoon/early evening hours and clear out overnight. MVFR conditions are expected in any heavier showers, with brief IFR conditions possible.
AIRMET Sierra for tempo mountain obscuration is in effect over the the southeast facing areas of the Big Island and east facing areas of Oahu. AIRMET Sierra for IFR conditions may also be needed for the southeastern slopes of the Big Island later today as showers periodically become heavy.

Marine

Moderate trade winds will gradually ease today and tonight, then become more southerly on Tuesday as troughing amplifies to the west of the state. Moderate southerly winds will develop in advance of a front Wednesday. The front will move into the western islands Wednesday night and Thursday, then weaken into a trough and shift westward Friday. Light to moderate northwest winds may briefly develop behind the front over the far western end of the state, otherwise moderate southerly winds should prevail into the weekend.
Surf along south facing shores will slowly decline today and tonight. A series of overlapping, long-period south swells will then move through the islands Tuesday into the weekend. This will be a long lived south shore event, with surf holding well above the summertime average Wednesday through the weekend.
A small, long-period northwest swell will peak today, then slowly decline Tuesday, giving north shore surf a slight boost. A series of reinforcing northwest swells will keep some small to moderate sized surf moving into north facing shores Wednesday through the weekend.
Surf along east facing shores will remain well below normal levels through the weekend.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov