Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Mostly cloudy with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 80 near the shore to around 68 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 67 near the shore to around 56 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs around 82 near the shore to around 70 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 79. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 63 to 68. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs around 81. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Cloudy with showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 67 to 75 in the valleys to around 62 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers. Lows 56 to 61 in the valleys to around 50 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 69 to 77 in the valleys to around 64 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Breezy. Cloudy with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 72 to 79. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 68. East winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 74 to 81. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 79. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 57 to 69. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 74 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A weak cold front moving into the northwest islands from the northwest will slowly drift down the island chain, stalling out over Maui County later today. Clouds and periods of numerous showers will develop from Kauai to Maui into Tuesday. Winds have shifted northeasterly will become locally breezy behind the front from Kauai to Molokai today, then return to moderate speeds and fairly typical trade wind weather from Tuesday through the end of the work week. Another cold front approaching the islands next weekend could shift winds more southerly and increase shower activity for the northwest islands and east to southeast slopes of the Big Island.

Discussion

The satellite picture this morning shows a weakening cold front moving through the northwest islands of Kauai and Oahu. Clouds and periods of numerous showers will spread down the island chain today, stalling out as the front diminishes over Maui County. An upper level jet stream will also produce some high level cirrus clouds across the Hawaii Region over the next few days.
The keys to the time of arrival or rainfall amounts with this event will play out in the smaller mesoscale over each island. Mainly with developing convective showers along the wind shear boundary along the weakening cold front bringing showers into north and east slopes of each island. Flood advisories are possible as rainfall amounts accumulate in area streams and roadways.
The cold frontal zone stalls and diminishes today, allowing stronger northeasterly winds to blow across the island chain. These winds will drive clouds and showers along the remnant frontal zone back westward over Oahu, Kauai and Niihau on Tuesday and Wednesday. Longer range guidance shows yet another weakening cold front approaching the islands from the northwest on Thursday and Friday. Cold air moving in with this front will break down the ridge north of the state and cause wind directions to veer from an easterly to a more southerly direction by Friday with a period of enhanced showers along the eastern and southeastern slopes of the Big Island by Friday. Another round of wet weather is expected with this next system by next weekend, mainly over east to southeast slopes of the Big Island and near Kauai and Oahu as the weakening front moves over the northwest islands.

Aviation

A weak cold front will continue to move across the islands today resulting in increased showers and periods of MVFR or lower conditions across mainly the western half of the state. Areas east of Molokai will generally see isolated to scattered showers as the front stalls near Maui. Moderate to breezy north to northeasterly winds behind the front will continue to slowly move down the island chain tonight.
AIRMET Sierra for tempo mountain obscuration will remain in effect for Kauai and Oahu through the morning due to persistent showers.
AIRMET Tango for moderate turbulence between FL200 and FL400 will remain in effect for areas west of Molokai and will need to be extended east today as the jet stream moves across the islands.

Marine

Clouds and scattered showers associated with a cold front near Maui County is expected to weaken and stall as it moves over Maui County waters today. Fresh to locally strong trade winds will build in behind the front but lighter east winds are expected over Big Island waters through the period, spreading to all waters by midweek as the high to the distant northeast weakens.
A large NNW swell (340 degrees) has rapidly built in overnight over the western half of the state, and a High Surf Warning (HSW) has been issued for shores most exposed to the swell, with a High Surf Advisory for shores less exposed. Observed readings from the nearshore NDBC buoys 51208 has peaked well above forecast guidance. While the predominant period of the primary NNW (340 degrees) swell train will be around 14 seconds, the proximity of near gale force winds over waters just NW of the area will introduce a wide spectrum of wave energy extending into the shorter periods, resulting in rough and choppy surf along exposed N facing shores. The increasing seas will require an SCA for most waters through Tuesday. The swell will transition increasingly northerly (360 degrees) as it gradually diminishes late Monday/Tuesday. This swell could lead to moderate surges in Hilo and Kahului harbors.
A small S swell will gradually decline over the next couple of days. A small to moderate long-period NW (320 degrees) swell is expected Wednesday night and Thursday, followed by the potential for a very large NW (320 degrees) swell by the end of the week.
Surf along east facing shores will remain rough and choppy as the trade winds build back this week. Although, east facing shores exposed to the north swell wrap will see a rise coinciding with the north swell.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 AM HST Tuesday for Niihau, Oahu North Shore, Kauai North, Koolau Windward, Molokai Windward, Molokai North.
High Surf Advisory until 6 AM HST Tuesday for Kauai Leeward, Waianae Coast, Molokai West.
High Surf Advisory until 6 AM HST Tuesday for Maui Windward West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 AM HST Tuesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters.
Small Craft Advisory until 6 AM HST Tuesday for Kaiwi Channel, Maui County Windward Waters, Pailolo Channel, Big Island Windward Waters.

Data Courtesy of NOAA.gov