West Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows 68 to 73 near the shore to around 61 above 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs 83 to 88 near the shore to around 74 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows 68 to 73 near the shore to around 59 above 3000 feet. East winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 72. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 78 to 87. East winds 10 to 15 mph. Chance of rain 40 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 71. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 69 in the valleys to around 58 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 72 to 81 in the valleys to around 64 above 4000 feet. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 62 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 64 to 73. East winds 10 to 15 mph shifting to the southeast after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 85. East winds up to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 63 to 72. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 64 to 75. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers. Highs 71 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 62 to 75. East winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Strong trades into Friday as frequent showers persist over Windward Maui and Big Island. A drying trend is anticipated Friday night into the weekend as locally breezy trades prevail.

Discussion

Strong 592dm ridge at 500mb maintains a 1033mb surface high centered near 35N/150W this afternoon. The gradient around this high will support continued strong trades into Friday. Sustained winds and a few gusts have reached the Wind Advisory threshold this afternoon in the windiest locales and favored downslope areas of the Big Island and Maui County. Embedded within the background of strong trades is a band of remnant frontal moisture taking aim directly on Windward Big Island. 24 hour rainfall amounts have averaged 1-3″ in this area, and that includes the drought-stricken Hamakua Coast of the Big Island where multiple stations reported in excess of 2″ with a peak observation of 3.15″ upslope of Laupahoehoe as of 1pm HST this afternoon.
The latest satellite trends and model guidance suggest this band of showers will not be budging during the next 24 hours, though subtle veering of wind to a more E direction than the current ENE during Friday suggests a gradual progression away from the Hamakua District an increasing focus on the South Hilo and Puna Districts as the day progresses. Overall, seems prudent to anticipate at least an additional 1-3″ over the same areas by this time tomorrow bringing 48-hour totals into the 2-6″ range. The same can be said for windward portions of Haleakala. Elsewhere over the smaller islands, visible satellite indicates considerably less organized and shallower clouds over. Nonetheless, showers have persistently regenerated over the terrain throughout the day, particularly over the Ko'olau Range of Oahu. This is probably attributable diminished boundary layer stability owing to enhanced moisture trapped beneath the inversion. Little penetration of showers into central Oahu has been noted this afternoon, but that will likely change as showers deepen during the nocturnal period.
A drying trend commences late Friday into the weekend as a band of particularly dry mid-level air currently centered along 25N advances into the area. Inversion heights likely crash down to 5kft or lower by early Saturday bringing an end to meaningful rainfall across the area. Trades weaken during this time beginning as early as Friday, which will still be quite gusty but not likely to be supportive of extending the Wind Advisory. Isolated 50 mph gusts are not out of the question in the very windiest locales, but confidence in reaching criteria tomorrow is otherwise low.
The next round of upper troughing commences during the first half of next week bringing potential for mid-week frontal passage and a period of wetter weather.

Aviation

Strong trade winds will continue tonight into Friday, however, they will be gradually decreasing throughout that time as the high pressure far northeast of the state slowly weakens and drifts farther eastward. Regional satellite imagery and model guidance suggests that moisture embedded within the trades will continue to produce occasional MVFR, including isolated IFR conditions, over windward portions of the eastern islands as showers move into the area. For the western islands, occasional MVFR conditions will be possible, but windward showers are expected to be less frequent.
AIRMET Sierra remains in effect for mountain obscuration across north through east sections of all islands. This AIRMET will likely be needed for portions of the central and eastern islands through tonight, but improving conditions across windward Kauai and Oahu could warrant dropping it for those islands later this afternoon or evening.
AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain below 10,000 feet. This AIRMET will likely be needed for the next several days.

Marine

A strong surface high north-northeast of the islands, is driving fresh trade winds across Hawaiian waters. The high will sink southeast toward 30N and weaken slightly veering winds to a more easterly direction. A Small Craft Advisory (SCA) remains in effect for a combination of winds and seas until tomorrow night. Some zones will drop out of the SCA tomorrow evening as winds and seas ease for zones around Kauai and Oahu. The high pressure will meander northeast of the state near 30N tonight into early next week while gradually weakening. Trade winds are expected to ease to moderate to locally strong speeds overnight and Friday then possibly to more gentle to fresh speeds over the weekend. A front approaching from the northwest early next week could veer the winds out of the southeast with winds weakening to more light to moderate levels. GFS is more progressive with the front and impacts than the EC thus confidence in the extended forecast is low.
The current short period northeasterly (030 to 050 degree) swell will gradually decline through Friday. The High Surf Advisory (HSA) remains in effect through tomorrow night. Rough, choppy east shore surf will continue to gradually decline through the weekend as local and upstream trade winds speeds ease. Another small, long period, northwest swell will fill in over the weekend which should provide a small uptick in surf along north and west facing shores.
A small, long period, south swell that peaked yesterday will slowly fade through Friday. Small background south and southwest swells will fill in over the weekend keeping surf from going flat.

Fire weather

Strong trade winds will continue tonight into Friday, however, they will be gradually decreasing throughout that time as the high pressure far northeast of the state slowly weakens and drifts farther eastward. Regional satellite imagery and model guidance suggests that moisture embedded within the trades will continue to produce occasional MVFR, including isolated IFR conditions, over windward portions of the eastern islands as showers move into the area. For the western islands, occasional MVFR conditions will be possible, but windward showers are expected to be less frequent.
AIRMET Sierra remains in effect for mountain obscuration across north through east sections of all islands. This AIRMET will likely be needed for portions of the central and eastern islands through tonight, but improving conditions across windward Kauai and Oahu could warrant dropping it for those islands later this afternoon or evening.
AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain below 10,000 feet. This AIRMET will likely be needed for the next several days.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Friday for all east facing shores.
Small Craft Advisory until 6 PM HST Friday for all Hawaiian nearshore waters.
Small Craft Advisory until 6 AM HST Saturday for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Kauai Now Weather is brought to you by Blue Hawaiian Helicopters.