West Kaua’i

Today: Partly sunny with isolated showers. Highs 84 to 89 near the shore to around 75 above 3000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Highs 84 to 90 near the shore to around 76 above 3000 feet. Northeast winds up to 15 mph shifting to the east in the afternoon.

South Kaua’i

Today: Mostly cloudy with isolated showers. Highs 80 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning. Highs 81 to 89. East winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Cloudy with scattered showers. Highs 73 to 82 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Cloudy with scattered showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 83 in the valleys to around 67 above 4000 feet. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 40 percent.

North Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 86. East winds up to 15 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with isolated showers. Lows 65 to 74. Southeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning. Highs 77 to 86. East winds up to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly cloudy with scattered showers. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with isolated showers. Lows 65 to 76. Northeast winds around 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 74 to 85. East winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A moderate trade wind flow will gradually become more stable today, as an area of low pressure west of Kauai moves away from the area. Showers will favor windward slopes, and while most leeward areas will be rather dry, spotty afternoon showers will develop along the Kona slopes of the Big Island. Trade winds will start to weaken on Thursday and will likely be disrupted on Friday, when a passing upper level disturbance is expected to produce isolated interior showers during the afternoon. A weakening front may move down portions of the island chain this weekend.

Discussion

A moderate and stable trade wind flow expected today. High pressure overhead will lead to a strengthening inversion that will produce stability, but the departing upper low will send a shield of high clouds over the island chain. The surface ridge north of the state will remain essentially unchanged and generate moderate trade winds. Guidance shows little organized moisture in the trade flow, which points toward modest windward and mauka rainfall along with a few afternoon showers across the leeward slopes of the Big Island. Drier and more stable conditions favor a decrease in showers on Wednesday.
Trade winds will start to decline on Thursday, as an approaching North Pacific front weakens the surface ridge north of Hawaii. The ridge aloft over the islands will hang on through the day, suggesting continued stable conditions and limited rainfall.
Trade winds will likely become disrupted Thursday night and Friday as the front advances. A fast-moving upper-level trough passing over the island chain will lead to some instability, but moisture may be lacking. As a result, day time sea breezes will likely lead to spotty interior showers Friday afternoon.
The shallow and weakening front may reach Kauai sometime Saturday and drift over other portions of the island chain Sunday. Timing with this feature remains highly uncertain, and the GFS and ECMWF show the aforementioned upper-level trough lifting to the northeast with ridging aloft build over the islands during this time. Since the frontal band will be very weak with no upper support, rainfall will likely be confined to windward and north slopes with little threat for flooding.

Aviation

Moderate trades persist for the next couple of days as an area of high pressure builds well north of the Hawaiian Islands. High clouds continue to meander across western islands from the southwest. Some isolated showers may develop along windward Big Island near PHTO and may result in brief periods of MVFR conditions. Otherwise, expect VFR conditions to prevail.
No AIRMETs are in effect.

Marine

A high pressure ridge north of the Hawaiian Islands will build through Wednesday, slightly increasing the trade winds to locally strong from Tuesday night into Wednesday. A trough and upper level disturbance west of the offshore waters will continue to produce isolated thunderstorms across the south and west offshore waters for a few more days. Moderate to fresh trade winds will strengthen slightly into the fresh to locally strong range through Wednesday, then steadily decline through Thursday as the ridge weakens and drifts south in advance of an approaching cold front farther north of the region.
A large reinforcing short to medium period north swell will continue to decline today. Surf heights will continue to fall as this north swell energy decreases. Winds and seas will remain below Small Craft Advisory criteria until Wednesday, where a combination of winds and seas will likely produce SCA conditions in most coastal waters and channel areas.
A gale low currently passing far north of the state will send the next large medium period north-northwest swell. This swell will build into the Hawaii region later tonight and peak late Wednesday. Surf heights will exceed advisory thresholds along exposed north and west facing shores. Advisory level surf could hold into Thursday, before steady declining. A reinforcing north- northwest swell is possible on Friday, which should help maintain moderate surf on Friday.
In the long range, a deep low pressure system is expected to develop to our north and northeast Friday into Saturday. This low will likely send a large north-northeast (020-030 degree) swell late this weekend. Due to the swell angle, heavy surges will be possible along north facing harbors such as Kahului and Hilo on Sunday.
A large north-northeast swell on Sunday may bring advisory level surf along east facing shores on Sunday. South facing shores will remain small throughout this week. A small long-period south- southwest swell is possible Friday into the weekend with a larger out of season south swell possible by early next week.

HFO Watches/Warnings/Advisories

None.