Photo Credit: Jason Weingardt

West Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 63 near the shore to around 52 above 3000 feet. Light winds. Chance of rain 40 percent.

Wednesday: Mostly sunny with scattered showers. Highs around 80 near the shore to around 68 above 3000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs around 78. Northeast winds around 10 mph in the morning becoming light. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 59 to 64. Light winds. Chance of rain 40 percent.

Wednesday: Mostly sunny with scattered showers. Highs around 79. Light winds. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Southeast winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 52 to 57 in the valleys to around 46 above 4000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny with scattered showers. Highs 67 to 75 in the valleys to around 62 above 4000 feet. Light winds. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 71 to 78. Southeast winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 55 to 64. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny with scattered showers. Highs 72 to 79. Northwest winds up to 10 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 71 to 78. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 53 to 65. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny with scattered showers. Highs 72 to 79. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A stubborn upper level low will gradually weaken and shift east today, allowing for a slow decrease in cloud cover, while winds also weaken across the state. Showers will favor windward areas this morning, then interior and leeward areas this afternoon. Another disturbance aloft could bring some showers into leeward areas late tonight and Wednesday, with light winds also bringing a few afternoon showers to leeward areas Wednesday afternoon. A cold front will usher in some cooler air and bring an increase in showers to north and northeast facing slopes and coasts Wednesday night through Friday as it moves through. Light to moderate trades appear in store for the weekend, with rain chances remaining highest over windward sections of the eastern islands.

Discussion

Currently at the surface, a 1028 mb high is centered around 1100 miles northeast of Honolulu, while a cold front is located around 900 miles west-northwest of Kauai. Moderate trade winds prevail across the island chain early this morning, strongest over the eastern end of the state. Infrared satellite imagery shows mostly cloudy conditions across much of the state, with pockets of lesser cloud coverage over the smaller islands. Radar imagery shows scattered showers moving into windward slopes and coasts, with mainly dry conditions in leeward locales. Main short term focus revolves around trade wind trends and rain chances during the next couple days.
The high northeast of the state will lift northeastward and further away from the islands during the next couple days, as a cold front approaches from the northwest. In response, the trades will ease across the state today, with the winds likely being light enough over the western islands and the more sheltered sections of the eastern islands to allow for sea breeze development this afternoon. Winds will ease further tonight with land breezes common statewide by daybreak Wednesday, followed by sea breeze development during the day. A cold front will then gradually push southeast down the island chain Wednesday night through Friday, ushering in moderate northerly winds which will slowly shift northeasterly by daybreak Friday. The front will stall out and dissipate in the vicinity of the Big Island on late Friday through Saturday, while a weak high slides by to the north of the state. Moderate northeast trades will hold on Friday, before easing into the light to moderate range over the weekend. High pressure north of the state could bring a slight increase in the trade wind speeds early next week.
As for the remaining weather details, showers will favor windward slopes and coasts this morning, with sea breezes allowing some interior and leeward shower development this afternoon. Showers should diminish fairly quickly this evening, with a few showers still moving into windward and southeast facing slopes of Maui and the Big Island. A shortwave trough approaching from the west may draw some deeper moisture northward later tonight and early Wednesday, increasing shower chances over leeward sections of the smaller islands as southwesterly boundary layer flow gets a boost from an approaching cold front. The shortwave trough is expected to exit east of the state Wednesday afternoon, with sea breezes bringing a few interior and leeward showers once again.
A cold front moving southeastward through the state will then usher in some cooler air and bring increasing showers to north and northeast facing slopes and coasts as it moves through Wednesday night through Friday. Model solutions are showing some differences in the progressiveness of the front Friday through the weekend, lowering forecast confidence. Overall, it appears that rain chances will remain highest over the eastern end of the state Friday through the weekend as the front stalls out and dissipates in this area, while the western islands may see very little rain as the drier post-frontal airmass settles in.

Aviation

Light to moderate easterly trades will gradually weaken today as high pressure north of the state moves east. Thus, afternoon sea breezes will likely develop along coastal regions.
Trade flow in the lower levels will keep shower activity mainly limited to windward areas this morning then transition to focus on interior regions by afternoon. Expect patches of mid level clouds today as an upper trough remains south of Hawaii.
Brief periods of MVFR ceilings and visibility will be possible in any of the heavier showers.
AIRMET Tango remains in effect below 8000 feet over and south through west of mountains for tempo moderate turbulence. These conditions will likely improve later this morning. AIRMET Tango also remains in effect for tempo moderate turbulence aloft between 120-FL280 for tempo moderate turbulence. See SIGMET PAPA series over the islands for areas of severe turbulence between Fl280-Fl350.

Marine

The high pressure system northeast of the islands will continue to move farther east today as a weakening cold front approaches the Hawaii region from the northwest. Wind speeds will blow from the east-southeast direction today and diminish over the next few days. Light to gentle westerly winds will filter into the region from tonight through Wednesday ahead of the approaching front. Land and sea breeze wind coverage will spread into near shore coastal waters from this afternoon through Wednesday. Moderate to locally fresh northerly winds will fill in as the front advances down the island chain Wednesday night through Thursday night, then winds will blow out of the northeast on Friday as the ridge builds in behind the front. Gentle to moderate east to northeast trade winds are forecast through the weekend.
Surf along exposed north and west facing shores will peak today just below High Surf Advisory levels as a long period northwest swell fills in. This swell will keep moderate surf heights along north and west facing shores today and tonight, then trend downward by Wednesday.
A more significant northwest to north-northwest swell is expected to move into the islands late Wednesday night through the second half of the week. Guidance shows a good sized area of gale- to storm-force winds focused towards Hawaii within the 310-340 degree directional bands lasting through Wednesday as the system moves eastward. Surf heights will likely exceed warning levels during the peak of this event from late Thursday through Friday, with swell heights decreasing through the upcoming weekend. Another overlapping moderate long period northwest swell will build in this weekend, possibly peaking at low end HSA thresholds by Sunday.
Surf along east facing shores will begin to ease through Wednesday as the trade winds diminish. Surf along south facing shores should gradually decline and return to background levels by Wednesday as the current small south swell dissipates.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov