Photo Credit: Jason Weingardt

West Kaua’i

Rest Of Today: Partly sunny. Windy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 82 near the shore to around 71 above 3000 feet. Southwest winds 10 to 30 mph increasing to 20 to 30 mph in the afternoon. Chance of rain 70 percent.

Tonight: Windy. Mostly cloudy with occasional showers. Lows around 64 near the shore to around 53 above 3000 feet. Southwest winds 10 to 30 mph shifting to the west 10 to 15 mph after midnight. Chance of rain 90 percent.

Wednesday: Mostly sunny. Isolated showers in the morning. Highs around 82 near the shore to around 70 above 3000 feet. West winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Today: Windy. Partly sunny with scattered showers. Highs around 81. Southwest winds 15 to 30 mph increasing to 25 to 30 mph in the afternoon. Gusts up to 50 mph. Chance of rain 50 percent.

Tonight: Windy. Mostly cloudy with numerous showers. Lows 60 to 65. Southwest winds 15 to 30 mph with gusts to 50 mph becoming west 10 to 15 mph after midnight. Chance of rain 70 percent.

Wednesday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs around 81. West winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Rest Of Today: Mostly cloudy. Windy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 70 to 78 in the valleys to around 65 above 4000 feet. Southwest winds 10 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Tonight: Windy. Mostly cloudy with occasional showers. Lows 53 to 58 in the valleys to around 47 above 4000 feet. Southwest winds up to 30 mph with gusts to 50 mph shifting to the west up to 20 mph after midnight. Chance of rain 90 percent.

Wednesday: Breezy. Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 69 to 77 in the valleys to around 64 above 4000 feet. West winds up to 20 mph. Chance of rain 20 percent.

North Kaua’i

Rest Of Today: Windy. Partly sunny with scattered showers. Highs 75 to 82. Southwest winds up to 30 mph increasing to 10 to 30 mph in the afternoon. Gusts up to 50 mph. Chance of rain 50 percent.

Tonight: Windy. Mostly cloudy with occasional showers. Lows 56 to 65. West winds 10 to 30 mph with gusts to 50 mph decreasing to 10 to 15 mph after midnight. Chance of rain 90 percent.

Wednesday: Breezy. Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 74 to 81. West winds 10 to 20 mph. Chance of rain 20 percent.

East Kaua’i

Rest Of Today: Windy. Partly sunny with scattered showers. Highs 75 to 82. Southwest winds 10 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 54 to 66. Southwest winds up to 25 mph with gusts to 50 mph shifting to the west up to 15 mph after midnight. Chance of rain 70 percent.

Wednesday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs 74 to 81. West winds up to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

An approaching front will produce breezy and gusty southwest winds today, along with bringing an increase in showers, especially for Maui County and the Big Island. The front will pass over Kauai tonight and weaken and dissipate near Oahu on Wednesday. Weak high pressure building over the island chain late Wednesday and Wednesday night will bring a drying trend. Mostly dry weather will then persist Thursday through early next week, as winds gradually pick up out of the south and southwest ahead of a slowly approaching cold front.

Discussion

Currently at the surface, a cold front is located around 250 miles west-northwest of Kauai, with a ridge of high pressure positioned a couple hundred miles south of the Big Island. The gradient between these two features is supporting moderate to breezy southerly winds across the island chain early this morning. Infrared satellite imagery shows broken stratocumuls moving northward into the islands, with cloud coverage the highest in leeward areas and over much of Maui County. Radar imagery shows scattered showers moving into south facing slopes and coasts, with coverage the highest over Maui County where a pre-frontal convergent band has set up. Main short term focus revolves around the need for a Wind Advisory today in advance of the approaching front.
The cold front to the west-northwest will track steadily eastward today, strengthening the south to southwest winds across the island chain. The latest guidance continues to indicate a low level inversion hanging on through much of the day, particularly over the western islands, while 850 mb winds increase to 45 to 50 knots by mid to late afternoon. Gustiness has already developed downwind of the higher terrain with wind gusts of 35 mph. The winds are expected to continue to strengthen this morning, peaking at advisory levels from mid morning into early this evening. As a result, a Wind Advisory has been issued through midnight HST tonight for most of the state with the morning forecast package.
The front will move into Kauai this evening, then stall out and dissipate near Oahu late tonight and Wednesday morning. This will lead to a gradual easing of the winds from west to east across the state, with moderate west-southwest flow expected in most areas by late Wednesday afternoon. The winds will ease further Wednesday night as a ridge builds northward over the islands, with light southerly winds expected on Thursday. A slow moving cold front will begin to approach far to northwest of the state Thursday night, eventually nearing Kauai early next week. As a result, we should see light to moderate southerly winds develop for Friday, increase to mostly moderate speeds by late in the weekend, with moderate to locally breezy conditions possible early next week.
As for the remaining weather details, we should continue to see showers moving into south facing slopes and coasts today in advance of the approaching front, with coverage the highest over Maui County where a pre-frontal convergent band is expected to remain. Maui County and leeward sections of the Big Island appear to be the main targets for shower activity tonight through Wednesday as the pre-frontal convergent band slowly shifts eastward. Meanwhile, fewer showers are expected across Kauai and Oahu today, until the trailing cold front leads to an increase in showers over Kauai late this afternoon and tonight, with increasing showers possible over Oahu after midnight into Wednesday morning.
The airmass stabilizes quickly late Wednesday and Wednesday night, with showers diminishing across the island chain. Mainly dry conditions should then persist across the entire state Thursday through early next week, with only a few light showers possible at times in the slowly increasing south to southwest flow.

Aviation

MVFR/IFR conditions with low cloud ceilings are favoring the the islands in Maui County this morning along a prefrontal convergence band. Predominantly VFR conditions remain in the forecast over Kauai, Oahu and the Big Island through the early morning hours. A cold front approaching Kauai from the northwest today will continue to strengthen southwest winds over all islands with stronger wind gusts expected to last through the evening hours. Shower bands are expected to develop as southwesterly winds increase today. In this southerly to southwesterly wind pattern we expect shower activity to favor the mountains peaks and south through west slopes of each island.
The cold frontal band will reach Kauai by this evening with MVFR conditions and showers spreading across the island. A large prefrontal convergence band will continue to develop over Maui County and the Big Island producing additional showers and periods of MVFR conditions through the evening hours.
AIRMET Sierra remains in effect for IFR conditions due to low ceilings and visibilities on the island of Lanai. These IFR conditions are being caused by a prefrontal convergence zone over the island. Expect these IFR conditions over Lanai to change to MVFR levels later this afternoon.
AIRMET Sierra also remains in effect for mountain obscuration due to low cloud ceilings affecting Molokai and Maui. This AIRMET for mountain obscuration will spread into the Big Island later this morning, and to Kauai by tonight as the cold front moves into the island.
AIRMET Tango remains in effect for moderate low level turbulence over mountains and along north through east sections of all islands due to strengthening southwest winds.

Marine

Fresh to locally strong south and southwest winds will hold through today as a cold front approaches. A Small Craft Advisory (SCA) is now in effect for most waters around the state due to strong winds and building seas from a large north swell. The cold front is forecast to move down the island chain tonight through Wednesday, then diminish. Light and variable winds return late Wednesday through Thursday. Winds will strengthen out of the south to moderate Friday before strengthen again to moderate to fresh Sunday into early next week as a couple of front passes by to the north.
Offshore NDBC buoys are hovering around 16 feet 16 seconds largely due to a large north- northwest swell (340-350 degrees) that is moving through the island chain. This swell will boost surf to low end warning levels today along north facing shores. A Marine Weather Statement has also been issued through today for harbor surges at Kahului and Hilo Harbors due to the large north swell. This swell is expected to decline tonight as a large, long- period northwest (310 deg) swell fills in from the northwest which will maintain advisory level surf Wednesday for north facing shores, and will bring west facing shores up to advisory level. This swell will increase further late Wednesday, leading to warning- level surf for exposed north and west facing shores through Thursday. A gradual downtrend is expected Thursday night through Friday, with heights dipping back below advisory levels on Friday. For the upcoming weekend, guidance shows a large, long- period west- northwest (300 deg) swell filling in Saturday, peaking Saturday night into Sunday before slowly trending down into early next week.
Surf along east facing shores will remain small due to the lack of trades locally and upstream of the state. The exception will be a rise in surf for shores exposed to the large northerly swells. Surf along south facing shores will come up late tonight through midweek due to a mix of fresh to strong south-southwesterly winds locally and a small, long-period south swell. A downward trend is expected through the second half of the week.

HFO Watches/Warnings/Advisories

Wind Advisory until midnight HST tonight for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Maui Windward West, Maui Leeward West, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island East, Big Island North.
High Surf Warning from 6 AM this morning to 6 PM HST this evening for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Koolau Windward, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
High Wind Warning until 6 PM HST Wednesday for Haleakala Summit, Big Island Summits.
Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.
Small Craft Advisory from 6 AM this morning to 6 AM HST Thursday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters.
Small Craft Advisory from 6 AM this morning to 6 AM HST Wednesday for Oahu Leeward Waters, Maalaea Bay, Big Island Leeward Waters.

Data Courtesy of NOAA.gov