West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 69 near the shore to around 60 above 3000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the morning. Highs 81 to 86 near the shore to around 73 above 3000 feet. Light winds. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Lows around 69 near the shore to around 59 above 3000 feet. Light winds.

South Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows around 70. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 78 to 86. Light winds.

Tuesday Night: Partly cloudy. Lows around 70. Light winds.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 60 to 68 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 73 to 81 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Isolated showers in the evening. Lows 60 to 67 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 20 percent.

North Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening. Lows 63 to 70. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 76 to 84. Light winds. Chance of rain 20 percent.

Tuesday Night: Partly cloudy. Lows 62 to 70. Light winds.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 62 to 73. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 73 to 84. Light winds.

Tuesday Night: Partly cloudy. Lows 62 to 73. Light winds.

Detailed Forecast

Synopsis

Stable and dry conditions with light southeasterly background winds will continue for the first half of the week. This will result in daytime sea breezes and nighttime land breezes each day. A weakening front approaching from the northwest could increase shower chances for the western islands Wednesday through Thursday, though there remains some uncertainty. Trade winds will build back into the region and strengthen from Thursday onward, bringing back periods of passing showers to windward and mountain areas that will favor the typical overnight to early morning hours.

Discussion

This afternoon, multiple low pressure circulation centers can be seen on regional satellite imagery in the North Pacific, near and north of 40N far north of the main Hawaiian Islands. A long surface frontal boundary stretches from the southernmost of these low pressure circulations southwestward to the International Date line to near 160E. High clouds ahead of the front, which is currently located about 350nm northwest of Kauai, have begun streaming over the western end of the state today. Meanwhile, a high pressure ridge remains in place over the island chain, which has resulted in yet another day of stable conditions and light southeasterly background winds prevailing over the state. Given the light background flow, daytime sea breezes have increased interior clouds over the islands today, but these interior clouds will clear tonight as land breeze circulations resume. Rainfall has been scarce within this dry, stable regime.
This stable pattern with light southeasterly background winds will continue for most areas through at least late Tuesday into early Wednesday. Throughout this time, daytime sea breezes will increase interior clouds over the islands each day, followed by land breezes clearing skies over the islands each night. Shower chances will remain limited, and any showers that do occur would be light.
Global models continue to show that the aforementioned cold front to our northwest will gradually weaken as it approaches over the next couple of days. It is then expected to move near Kauai and stall on Wednesday. As this occurs, shower activity will likely increase over Niihau and Kauai for 12 to 24 hours, until the front breaks apart and drifts back westward away from the islands. Differences between the various global models remain, with the ECMWF notably showing wetter trends for the islands in Kauai County. The GFS, however, continues to favor a drier solution where the weakening boundary stalls and then moves back westward away from the state before reaching the Garden Isle.
A high pressure system will build in north of the state for the second half of the week, increasing easterly trade winds across the region. Expect some southeasterly winds to linger on Thursday morning, with winds becoming more easterly and stronger from Thursday night into next weekend. As the ridge over the islands lifts northward, our typical trade wind shower activity returns with brief passing showers forecast along windward and mountain areas, favoring the overnight to early morning hours each day.

Aviation

A light southeasterly wind regime will continue through Tuesday, allowing daytime sea breezes and overnight land breezes to occur. VFR conditions are expected under a relatively dry and stable air mass through Tuesday. A thin veil of high clouds will move over the state from west to east starting this evening.
No AIRMETs are in effect and none are expected.

Marine

A weak surface ridge will remain over the area through Tuesday and maintain light to moderate southeast background flow. This pattern will allow for daytime sea breezes and nighttime land breezes along waters adjacent to the coasts. A cold front is projected to approach Kauai from the northwest on Wednesday and is expected to stall and quickly weaken to a trough by late Wednesday. The trough is then expected to retrograde back westward towards the end of the week as a ridge of high pressure builds north of the state. Moderate to locally strong easterly trade winds is expected to return Friday into Saturday.
The current, large, long-period northwest (310-320 degree) swell will steadily decline through tonight. A High Surf Advisory is now in effect through tonight for exposed north and west facing shores of most islands. A series of northwest to north-northwest (310-330 degree) swells are expected during the second half of the week, with each pulse becoming slightly bigger and veering towards the north- northwest direction. The first pulse will be filling in on Wednesday and will be more of a medium period swell out of the northwest. Surf heights may approach advisory thresholds, but at this time we are expecting surf heights to stay just below advisory thresholds on Wednesday. A slightly larger and longer period pulse is expected on Thursday out of the northwest followed by a slightly larger north-northwest on Friday. Surf heights should exceed advisory thresholds around Thursday with surf heights likely holding above advisory thresholds through Saturday.
East shore surf will remain small through Thursday due to weak winds, then become choppier as trade winds increase Friday through the weekend. Expect minimal background energy for south facing shores through much of the week.

Fire weather

Critical fire weather conditions are not expected this week. Although stable and dry conditions will persist through mid-week, winds will be light and variable, preventing critical fire weather concerns. Locally breezy trades will return during the second half of the week, but increased relative humidity is expected.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for north and west facing shores of Niihau, Kauai, Oahu, and Molokai, for north facing shores of Maui, and for west facing shores of the Big Island.