Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 81 near the shore to around 69 above 3000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 69 near the shore to around 63 above 3000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs around 81 near the shore to around 69 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 78. East winds 10 to 15 mph. Chance of rain near 100 percent.

Tonight: Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 69. East winds 10 to 15 mph. Chance of rain 90 percent.

Wednesday: Partly sunny with scattered showers. Highs around 78. East winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 68 to 75 in the valleys to around 59 above 4000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 62 to 67 in the valleys to around 59 above 4000 feet. Southeast winds up to 20 mph. Chance of rain 90 percent.

Wednesday: Breezy. Mostly cloudy with numerous showers. Highs 68 to 75 in the valleys to around 59 above 4000 feet. Southeast winds up to 15 mph shifting to the east up to 25 mph in the afternoon. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 71 to 80. Southeast winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 65 to 70. Southeast winds up to 25 mph. Chance of rain 90 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 71 to 80. East winds up to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Breezy. Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 71 to 79. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 60 to 72. East winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 71 to 79. East winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The flooding threat will continue today and may linger into Wednesday for the western end of the state as deep tropical moisture pools northward over the region. Drier air and strong easterly trade winds are expected Wednesday into the second half of the week as low pressure to the west drifts away from the area. A wetter trade wind pattern is possible this weekend as an upper disturbance settles southward into the area.

Discussion

Deep tropical moisture pooling northward over the islands in response to deep low pressure located a few hundred miles to the west supports the wet pattern continuing. The upper air sounding at Lihue reflected this moisture and was saturated through much of the column with a PW coming in at 1.8″. Bands of heavy rain continue to develop and lift northward over Kauai County early this morning, with peak rainfall rates ranging from 1 to 2 inches at the gauges. Elevated streams combined with saturated soils and additional heavy rainfall expected will keep the threat of flash flooding up today. Although the overnight activity eased over leeward Oahu, another round of heavy showers is possible today as the island remains in a confluent east-southeast flow. The same is possible for the southeast facing slopes of the Big Island. At Hilo, some drier mid- to upper-level air above a weak temperature inversion was depicted between 9000 and 10000 ft (PW of 1.55″). Although a few bouts of mixed precip can’t be ruled out over the Summits today where any convection forms, this drier air that has moved in reduced forecast confidence enough to cancel the Winter Weather Advisory.
Guidance remains in good agreement and shows the plume of deep tropical moisture over the islands and trough to the west remaining in place into Wednesday, then beginning to shove away from the area through the second half of the week. If this is realized, the flood threat may linger into Wednesday, especially for Kauai County. Some mid-level dry air is shown spreading westward into Oahu Wednesday, which should translate to a gradual improving/drying trend from east to west. For the second half of the week, the east-southeast low-level flow will back to a more typical easterly trade wind direction. Wind speeds may reach the advisory level as strong high pressure (1040 mb) sets up north- northeast of the state. For the upcoming weekend, guidance shows an upper trough moving in from the northeast. Lowering upper heights and increasing instability associated with this upper feature could support increasing trade wind shower coverage. Although the bulk of the showers will favor windward areas, the brisk trades will manage to carry some into leeward areas, especially through the overnight and early morning periods this weekend.

Aviation

Abundant low level moisture and unstable atmosphere will maintain showers with locally heavy rainfall and isolated thunderstorms across much of the state. This pattern will continue MVFR, and localized embedded IFR, conditions today. This will continue the need for AIRMET Sierra due to tempo mountain obscuration at times through the TAF period.
Additionally, strengthening trades will increase the potential of low-level mechanical turbulence downwind of mountains, especially for the central smaller islands today. Therefore, AIRMET Tango for low-level moderate turbulence continues for Maui, Molokai, and Oahu.
A period of potential light ice continues in a layer between 150/FL250, as a band of mid and upper level moisture lingers across the state.

Marine

A high pressure ridge building in from the northeast will produce strong to near gale force trade winds across Hawaiian waters through the end of the week. A developing low pressure system west of the state and abundant tropical moisture will produce periods of showers, heavy at times, with isolated thunderstorms across the region through Wednesday. A Small Craft Advisory remains in effect for most waters due to a combination of winds and seas through at least Friday.
Surf along east facing shores will remain rough through the week due to persistent and strong trade winds over and upstream of the Hawaiian Islands. Surf heights along east facing shores are reaching High Surf Advisory levels today through Wednesday due to strong winds. East shore surf will likely hold at or near low end advisory levels through the weekend.
A series of small, medium to long period northwest (310-330) swells will move through the island waters through the weekend. Expect surf heights along north and west facing shores to remain well below the seasonal average through Sunday. South shore surf will also remain small through the weekend.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward.
Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters except Maalaea Bay,

Data Courtesy of NOAA.gov