West Kaua’i

Today: Partly sunny with scattered showers. Highs 82 to 88 near the shore to around 74 above 3000 feet. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 68 to 73 near the shore to around 61 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 60 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 82 to 87 near the shore to around 73 above 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs 79 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 72. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly cloudy with numerous showers. Highs 77 to 85. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy with numerous showers. Highs 72 to 80 in the valleys to around 64 above 4000 feet. Light winds becoming northeast up to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then showers after midnight. Lows 63 to 69 in the valleys to around 58 above 4000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Wednesday: Windy. Cloudy with showers. Highs 70 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 20 mph increasing to 10 to 30 mph in the afternoon. Chance of rain 90 percent.

North Kaua’i

Today: Mostly cloudy with numerous showers. Highs 74 to 85. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows 64 to 72. East winds up to 10 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly cloudy with numerous showers. Highs 73 to 84. East winds up to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly cloudy with numerous showers. Highs 72 to 84. Northeast winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then showers after midnight. Lows 64 to 75. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Wednesday: Mostly cloudy. Breezy. Showers in the morning, then numerous showers in the afternoon. Highs 69 to 82. Northeast winds 10 to 20 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

An upper level low southwest of the islands will pull moisture over the eastern half of the state through Tuesday. This feature, along with a developing surface trough, will bring an increased chance of heavier showers Tuesday night through Wednesday, especially for windward portions of Maui and the Big Island. The chance of heavy rainfall diminishes late Wednesday into Thursday, though breezy showery trades will persist. A brief period of stable and drier trade wind conditions is expected on Friday, followed by more showery weather into the weekend as a cold front advances toward the island chain.

Discussion

Latest satellite imagery shows thick mid to upper level clouds streaming in from the southwest from Oahu to the Big Island causing overcast conditions. Near the surface, moderate trades continue to push typical scattered showers along windward and mauka areas especially over the western end of the state as evident on radar. Meanwhile on the eastern end of the state some showers are beginning to fall across east and southeast portions of the Big Island. With freezing levels around 13Kft to 14Kft a wintry mix of rain and snow at the summits of Mauna Loa and Mauna Kea is possible. A Winter Weather Advisory remains in effect through 6PM this evening.
An upper level trough to the northwest deepens and a surface trough to the southwest of the Big Island, will continue to produce unstable conditions aloft. This is conducive to some heavy rain developing south of the Big Island, in association with the aforementioned surface trough. However, uncertainty remains an issue. The GFS is still a little more bullish with the intensity than the ECWMF, though it has been trending slightly weaker with the last couple runs. This pocket of deep moisture should lift northward late tonight into Wednesday, causing conditions to deteriorate further for windward portions of the Big Island and Maui. Strong trades, combined with deep moisture and instability aloft, may lead to a periods of heavy rainfall for these areas and a Flood Watch may be needed late tonight through Wednesday. The limiting factor will be if current trends hold, flooding will be limited and the Flood Watch wouldn't be necessary. Forecast rainfall totals currently range from around an inch with the ECMWF's weaker forcing to around two inches from the GFS.
As for the rest of the islands, tonight through Wednesday, the surface high building far north of the state will bring strong trades with scattered to numerous showers that will affect both windward and leeward sides of the islands. The flooding threat remains low over the smaller islands due to the speed these showers will be moving and the lack of forcing.
Any potential threat for heavy rain will decrease late Wednesday, but breezy and wet conditions are expected into Thursday. The strong surface high passing to the north will maintain breezy trade winds, and even though PWATs will be decreasing, both the GFS and ECMWF keep abundant moisture around the islands, pointing to a rather wet pattern.
A brief period of stable and drier trade wind conditions is expected on Friday, followed by the potential for more showery weather into the weekend and early next week as a cold front approaches the island chain. Once again models vary on timing and location so please pay attention for further updates.

Aviation

Trades will strengthen and back to the east northeast. Low cigs and trade wind SHRA will be focused over windward and mauka locations. As deeper moisture streams up from the southeast, SHRA will increase across the island chain. IFR/MVFR conds are possible in these heavier SHRA. Some locations on the western side of the state may stay VFR.
AIRMET Sierra while not in effect at this time, will likely be needed for portions of the island chain through Thursday.
AIRMET Tango is in effect for mod turb in the mid to upper levels.
AIRMET Zulu is in effect for some light icing due to the influx of high clouds.

Marine

A front about 600 nm miles northwest of the Kauai coastal waters (about 450 nm northwest of the offshore waters) will continue to move to the east, approaching the region over the next couple of days. The front is pushing the ridge to the north of the region to the east which will result in a weakening of the winds today, as the winds also veer to the east-southeast. The front is expected to weaken as it enters the northwest offshore waters later today, and then lift to the north tonight and tomorrow. Near gale-force winds are possible behind the front in the northwest offshore waters. An upper level trough over the islands, combined with moisture surging northward on the east side of said upper trough could produce thunderstorms over the offshore waters.
Behind the front, a new high building north of the islands will help trades strengthen across the region to fresh to locally near gale speeds. Combined with incoming northwesterly swells, expect winds and seas to exceed Small Craft Advisory (SCA) thresholds for exposed coastal waters Wednesday into Thursday. Some of the high resolution models suggest that SCA level winds could reach some of the typical windier waters later today, however with confidence low, am holding off on issuing the SCA at this time.
A small, short period NE and small, medium period NW swell will continue to slowly decline this morning. Overlapping NW to NNW swells rest of this week will keep surf heights boosted along exposed N and W facing shores. A pair of small to moderate, long period NNW (310-340 degree) swells will arrive today, peaking Wednesday near or above High Surf Advisory (HSA) levels. Buoy 51001 started to pick up the 16 second energy around 1am, around the same time the WaveWatch guidance suggested, but a little smaller than guidance. Surf is then expected to gradually declining Wednesday night through the end of the week. Another overlapping small, short to medium period N (350-010 degree) swell arrives from Thursday into Friday. Then another moderate, long period NW (310-330 degree) swell arrives Friday, peaking near HSA thresholds over the weekend.
Surf along E facing shores will continue to decline this morning due to the weakening of the local and upstream trade winds. As a new high pressure builds N of the state Wednesday through Thursday, rough and choppy surf along E shores could near HSA levels. For S shores, periods of tiny background south swell energy will continue to move through keeping surf from going flat.

Fire weather

Moderate trades and higher humidities will maintain conditions below critical fire weather thresholds. Wet conditions are expected into Thursday, with heavy rainfall possible over recent burn areas on the Big Island.

HFO Watches/Warnings/Advisories

Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.

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