Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny. Highs around 83 near the shore to around 70 above 3000 feet. East winds up to 15 mph.

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 67 near the shore to around 57 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Highs around 83 near the shore to around 71 above 3000 feet. East winds up to 15 mph.

South Kaua’i

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 78 to 83. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 66. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 78 to 84. East winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 70 to 77 in the valleys to around 62 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 65 in the valleys to around 55 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 70 to 77 in the valleys to around 63 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 73 to 83. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 60 to 69. Southeast winds up to 10 mph. Chance of rain 40 percent.

Wednesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 83. Southeast winds up to 15 mph. Chance of rain 30 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 70 to 81. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 61 to 71. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny with isolated showers. Highs 70 to 80. East winds up to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A high pressure system passing eastward, north of the state, will produce moderate to breezy trade winds into Wednesday. An approaching cold front will shift these winds from a more east to southeast direction from Wednesday afternoon into the weekend. A passing upper level low/trough will likely produce some rain shower enhancement across all islands on Friday and Saturday, favoring the overnight hours. All slopes of the Big Island should see a small boost in rainfall activity for the same time period. Expect wet weather trends starting early next week as a trailing cold front sweeps into Hawaiian waters.

Discussion

The satellite picture this morning starts with upper level water vapor imagery, where a weak upper trough near the Big Island continues to slowly drift eastward away from the islands. Infra-red imagery shows a few fairly stable cloud bands just upstream of the islands riding in on the easterly trade winds. Scattered showers will continue to develop mainly over windward and mountain areas through the early morning hours. Drier trends are forecast for most of the daylight hours.
A high pressure system northeast of the Hawaiian Islands will continue to drift eastward away from the state over the next few days. Expect moderate to breezy trade winds to peak today and then decrease as the high center drifts farther away from the islands from Wednesday onward. A cold frontal system approaching the islands from the northwest will cause the ridge to lift and weaken just north of the state. This change in surface pressure patterns will produce a trend to southeasterly winds over the western islands with east to southeast winds near the Big Island and Maui. Typically these southeasterly winds are drier for all the smaller islands falling into the leeward rain shadow of the Big Island mountains. However, shower activity will pick up a bit along the east to southeast slopes of the Big Island as winds drive available tropical moisture up the mountain slopes near the Ka'u and Puna Districts on the Big Island.
On Thursday, a cold front will approach the state from the northwest, the forward motion on this weakening front will stall out far to the northwest of Kauai in the latest operational model runs. A trapped cold pool south of the subtropical ridge will form a cut off low pressure system just west of Kauai. This upper low will then sweep across the islands from west to east on Friday and Saturday, unstable conditions under this cold core low will briefly increasing shower trends across the state. The continued east to southeasterly wind flow pattern will likely limit these showers to windward slopes of Kauai, Oahu, Molokai, and Maui. However, a boost in island wide shower trends are likely for the Big Island as leeward sea breezes and windward trade winds produce enough upslope forcing for brief periods of shower activity in the Friday and Saturday afternoon to early evening hours.
In the extended range forecast for early next week, we continue to see the potential for more wet weather riding into the Hawaii Region on the tail end of a passing cold front. Model solutions at this range tend to struggle with the details from run to run. We are taking a blended model approach to reduce the errors. Look for increasing rainfall trends at this point with moderate confidence. Island by island weather impacts for early next week will evolve over time, stay tuned for updates as the forecast time period grows shorter.

Aviation

Moderate to breezy easterly trade winds will prevail today through tomorrow as high pressure to the north of the state moves eastward. A relatively dry and stable airmass will limit shower activity, with only isolated to scattered light showers favoring windward and mauka areas. VFR conditions will prevail, except for within passing showers.
AIRMET Tango for tempo moderate mechanical turbulence lee of the island terrain is in effect this morning. This AIRMET will likely need to remain in effect through today.

Marine

Fresh to strong easterly trades will continue today, then gradually shift out of the east-southeast tonight through midweek due to a weakness forming in the ridge to the north. Although the winds will ease into the light to moderate range over the western end of the state during this transition, expect the strong winds to hold over the windier waters around Maui County and the Big Island. The Small Craft Advisory has been expanded to account for this by including the Big Island and Maui Windward waters where accelerations typically occur with this wind direction. Guidance remains in decent agreement and shows this wind pattern holding into the upcoming weekend as a couple of fronts pass far north of the islands.
Surf along exposed north and west facing shores will hold near the seasonal average through Wednesday (another northwest pulse arriving tonight), then trend back up to advisory levels late Wednesday night into Thursday as a fresh, long-period northwest swell arrives from a hurricane-force system centered around 1700 nm to the northwest this morning. Recent satellite data showed a large area of gale- to storm-force northwest winds associated with this system focused at the islands within the 310-330 degree directional bands. SOFAR drifter buoys reflected this with seas near the center of the fetch coming in around or just over 30 ft, which is near predicted levels. This swell will hold around the advisory levels Friday as it moves through, then slowly ease over the weekend.
Surf along east facing shores will steadily climb through the week due to a combination of the trades locally and the upstream trade wind belt expanding with fresh to strong breezes.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov