West Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 67 near the shore to around 57 above 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Sunday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 79 to 87 near the shore to around 74 above 3000 feet. Light winds. Chance of rain 20 percent.

Sunday Night: Mostly clear. Lows around 67 near the shore to around 57 above 3000 feet. Light winds becoming northeast up to 15 mph after midnight.

South Kaua’i

Tonight: Mostly clear. Lows around 67. Southeast winds up to 10 mph in the evening becoming light.

Sunday: Sunny and haze. Highs 81 to 87. Northeast winds up to 15 mph.

Sunday Night: Mostly clear. Isolated showers after midnight. Lows around 68. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Partly cloudy. Lows 57 to 67 in the valleys to around 55 above 4000 feet. Light winds.

Sunday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 74 to 80 in the valleys to around 66 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy with scattered showers. Lows 58 to 67 in the valleys to around 56 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly clear. Lows 60 to 67. South winds up to 10 mph in the evening becoming light.

Sunday: Sunny and haze. Highs 75 to 83. Northeast winds up to 10 mph.

Sunday Night: Partly cloudy with isolated showers. Lows 61 to 69. Southeast winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly clear. Lows 61 to 70. South winds up to 10 mph in the evening becoming light.

Sunday: Sunny. Haze through the day. Isolated showers in the afternoon. Highs 75 to 85. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

Sunday Night: Partly cloudy with isolated showers. Lows 61 to 72. Northeast winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Relatively dry conditions will persist the next couple of days under hazy and partly cloudy skies. Recent more humid southerly flow will transition to slightly drier gentle trade winds going into Monday. Trades will strengthen to more breezy magnitudes from Tuesday through the remainder of next week. Showers will become more frequent each subsequent day next week, mainly focusing on windward areas and across upslope mauka. Late week rain chances will increase as residual moisture from a remnant boundary moves in from the east as the resident atmosphere becomes more unstable.

Discussion

Deep upper to mid layer ridging sits atop the islands this evening. This will maintain stable conditions as, despite several days of this more humid southerly flow, the islands lie within a fairly dry air mass (by early March standards). A northeast-to-southwest orientated surface ridge axis extending from a 1030 mb high located about 1,500 miles northeast of the area is laying across the state. This afternoon's ASCAT pass verified the presence of this ridge axis as persistent moderate east to southeast winds across eastern islands and surrounding waters become southerly over the western half of the chain. The ridge aloft is maintaining very stable conditions with sparse available moisture as evidenced by the statewide empty rain gauges. The only caveat were the few windward and mauka Kauai rainfall gauges that picked up less than a tenth of 24 hour rainfall. Generally, southerly winds have kept island-wide dew points elevated (average coastal upper 60s) thus making it feel more humid by winter standards. The greatest concentrations of volcanic haze (vog) remain confined to Maui County and leeward Big Island but recent GOES GeoColor daytime imagery did depict haze creeping into eastern Oahu late this afternoon. As the surface ridge axis travels north tonight, east winds filling in underneath it will aid in lowering dew points to more seasonable lower to middle 60s while transporting vog further west over Oahu into Monday. Thus, Sunday's conditions will be less sticky but more hazy over Oahu and Kauai.
The surface ridge will move north through early next week as a stronger area of high pressure develops far to the northwest. This will allow gentle to locally breezy trades to develop across the entire island chain Sunday. Persistent upper ridging aloft will maintain stable and rather dry conditions the next couple of days. The highest chance of any rain will be across windward-facing coastal and mauka area and at higher elevation. As trades fill in from the east tomorrow, Kauai's leeward areas may experience thicker afternoon clouds and occasional light showers. Vog concentrations will likely thin out as strengthening trades better mix out haze through a deeper boundary layer. Trade winds will strengthen from Monday into Tuesday.
A new front approaching from the northwest Monday will likely become parallel to the upper level westerlies and dissipate just before it reaches the state. Surface high pressure will move in north of the state Tuesday and the resultant downstream pressure gradient from the high over the islands will produce several days of gusty, breezy trades. Stable conditions will generally remain the theme Monday, but windward locales will experience more overcast and frequent shower activity Tuesday and Wednesday. Residual moisture from the diffuse frontal boundary north of the state (mentioned above) will sag south toward Kauai and likely increase windward Kauai's precipitation chances Tuesday. In addition to the remnant frontal moisture over the north nearshore waters, ribbons of higher moisture from the east will periodically advect in on well-established trades later in the week. There will be a touch more instability in response to lowering heights (cooler temperatures aloft) in association from a trough passing far north of Hawaii in tandem with the weaker southern branch of the polar jet passing over the state. This less stable and more moist scenario should increase the probabilities of a more wet trade wind pattern during the second half of next week.

Aviation

A weak surface ridge over the state will produce light to moderate southerly flow across the western islands and southeasterly flow across the eastern islands tonight. Moderate easterly trade winds fill in by Sunday.
VFR conditions will prevail with no AIRMETs expected.

Marine

A regime change will occur over the next 24-48 hours. High pressure building N of the islands will lead to fresh to near gale-force trade winds that will remain in place for the foreseeable future. In the short term, a ridge of high pressure near Kauai and Oahu will change little as a front passes to the NW, with light and variable winds over Kauai and Oahu waters, and light to moderate E-SE winds over Maui and Big Island waters. By late Sunday, strong (1035 mb) high pressure will build N of the islands, and move slowly E through the week. A Small Craft Advisory will be needed for all waters as winds strengthen, and short-period wind waves increase to near 10 feet.
The current NW swell will continue to decline through the remainder of the weekend, with a new NW swell building Monday potentially leading to advisory-level surf at its peak. NW swell will diminish Tuesday and Wednesday, with another NW swell around Friday likely leading to advisory-level surf. A small S swell is possible tomorrow and Monday. Choppy surf along E facing shores will increase in response to the building trade winds supporting short-period wind waves.

HFO Watches/Warnings/Advisories

None.