West Kaua’i

Tonight: Mostly clear. Isolated showers after midnight. Lows around 72 near the shore to around 63 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs 84 to 90 near the shore to around 75 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Mostly clear. Lows around 71 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers after midnight. Lows 69 to 76. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs 78 to 88. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly clear. Lows 68 to 75. Northeast winds around 15 mph.

Kaua’i Mountains

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 68 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy. Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 72 to 79 in the valleys to around 66 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

Saturday Night: Partly cloudy. Breezy. Scattered showers after midnight. Lows around 67 in the valleys to around 59 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Breezy. Partly cloudy in the evening, then mostly cloudy with scattered showers after midnight. Lows 63 to 74. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 68 to 84. East winds 10 to 20 mph. Chance of rain 70 percent.

Saturday Night: Partly cloudy. Isolated showers after midnight. Lows 63 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Breezy. Partly cloudy in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 75. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 84. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday Night: Partly cloudy. Scattered showers after midnight. Lows 64 to 75. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A plume of moisture associated with now Tropical Storm Pena well south of the islands brought heavy rainfall to windward areas of the Big Island. While the deepest moisture has shifted off to the west, expect enhanced clouds and showers to continue into Saturday morning favoring Maui and Hawaii Counties. A second tropical disturbance will pass to the south of the state early next week, possibly enhancing shower activity to southern portions of the Big Island. The next best chance for statewide shower chances arrives late next week.

Discussion

Tropical Storm Pena formed late this morning 650 miles southeast of South Point, HI. Mid level ridging north of the state will steer this cyclone west for the next several days, staying well south of Hawaii. A plume of rich moisture tied to Pena which brought heavy rainfall to the Big Island over the last 24 hours has largely shifted to the west, but trades and moist low levels will keep shower chances going for windward areas of Hawaii and Maui into Saturday. Additional showers are possible around Kona where sea breeze convergence is occurring this afternoon.
A second disturbance behind the tropical storm will send another plume of deeper moisture westward Sunday into Monday. Guidance generally keeps this south of the Big Island, but it is expected to pass sufficiently close to keep an eye on. Shower chances increase for southern portions of windward Big Island Sunday night and Monday morning, but rainfall amounts will fall well short of the 2 to 5 inches that fell in BI windward areas in the last 24-30 hours.
The ridge to the north will settle farther southeast as the week wears on. Drier east northwest low level flow and lower inversion heights will keep shower chances limited mostly to windward areas of the BI and windward and mauka areas of the smaller islands. A surface front will reach the northern islands Thursday and the southern islands Friday. Some increase in shower potential is possible, but the strong ridging in place should limit chances for widespread rain.

Aviation

Breezy to strong trade winds will persist across the islands through the forecast period. Low clouds and showers riding in on the trades will maintain lower ceilings and frequent windward showers especially tonight. Conditions could improve slightly later tomorrow as drier air moves in.
AIRMET Sierra is in effect for mountain obscuration across windward Big Island and windward Maui. This AIRMET could continue through much of the night.
AIRMET Tango remains in effect for moderate turbulence within the lee of higher terrain the next few days.

Marine

Fresh to strong trade winds with periods of near gales in the channels will prevail through the weekend as high pressure persists north of the state. A Small Craft Advisory (SCA) remains in place for all Hawaiian Waters due to a combination of winds and elevated seas through Saturday night. The SCA will likely remain in place through at least Sunday night as Tropical Storm Pena passes several hundred miles to the south and keeps the local pressure gradient tight. Winds are expected to ease slightly late Monday and Tuesday as the ridge to our north erodes and Pena moves away to the southwest. The SCA will likely be trimmed back to the typical windy waters around Big Island and Maui at that time. Trade winds are expected to strengthen again on Wednesday.
A north-northwest swell will continue a slow decline through Saturday, and surf along exposed north and west facing shores has fallen below High Surf Advisory thresholds. A reinforcing medium- period energy out of the north-northwest (325 to 340 degree) should arrive late Saturday into Sunday. Surf should reach advisory thresholds during the peak of the swell Sunday morning. Another large northwest to north-northwest swell is Wednesday or Thursday.
A small south-southwest swell should produce surf slightly above seasonal average through Saturday. A tiny pulse from the south- southeast may maintain south shore surf near seasonal average Sunday and Monday, followed by background level surf through the remainder of the week.
Rough surf along east-facing shores will hold around seasonal average through much of the week. Select northeast exposures should see long- period energy from the declining north-northwest swell into tonight.

Fire weather

An easterly wave passing south of the islands will continue to bring elevated humidity levels and into Saturday morning. Fire weather conditions will remain below critical thresholds into next week. Temperature inversion heights will drop from 9-10 kft today to 6-8 kft for much of next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Sunday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Big Island Windward Waters, Kaiwi Channel, Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters, Maalaea Bay, Maui County Leeward Waters, Maui County Windward Waters, Oahu Leeward Waters, Oahu Windward Waters, Pailolo Channel.

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Data Courtesy of NOAA.gov