Photo Credit: Braden Jarvis

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs around 84 near the shore to around 74 above 3000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 65 to 70 near the shore to around 56 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs around 85 near the shore to around 75 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82. Northeast winds 15 to 25 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 69. East winds around 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny with isolated showers. Highs around 83. East winds around 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 77 in the valleys to around 66 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 59 in the valleys to around 51 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Thursday: Partly sunny with scattered showers. Highs around 78 in the valleys to around 67 above 4000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

North Kaua’i

Today: Breezy. Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 83. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 59 to 68. East winds 10 to 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny with scattered showers. Highs 77 to 84. East winds 10 to 15 mph. Chance of rain 30 percent.

East Kaua’i

Today: Breezy. Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 75 to 81. Northeast winds 10 to 20 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 57 to 70. East winds 10 to 15 mph. Chance of rain 40 percent.

Thursday: Partly sunny with scattered showers. Highs 76 to 82. East winds 10 to 15 mph. Chance of rain 30 percent.

Detailed Forecast

Synopsis

A strong high pressure system far north of the Hawaiian Islands will linger today with breezy to locally strong trade winds in the forecast. This high will then weaken from Thursday through Saturday producing more moderate trade winds across the island chain. Shower activity will favor windward and mountain locations, especially during the overnight and early morning hours each day through Saturday. As winds veer southeasterly early next week, shower chances will decrease a bit before increasing again by Tuesday as another low develops to the northwest of Kauai and slowly passes by just north of the island chain.

Discussion

The satellite water vapor channel continues to show a weakening sub tropical jet stream over the islands. This jet stream is positioned along the southern edge of a long and narrow upper level trough. Jet stream divergence will continue to spread high cirrus clouds over the state through the morning hours with diminishing ice crystal cloud coverage into Thursday as the jet slowly drifts eastward and weakens over the Hawaii region.
In the short range forecast, a strong high pressure system will linger north of the state producing breezy to locally strong trade winds today. This ridge will weaken from Thursday into Saturday with a slight decrease in trade wind strength. Upper level lows embedded within the upper trough will continue to enhance trade wind shower activity across Hawaii likely through Thursday. One of these stronger lows will produce a low level trough near the Big Island and Maui on Thursday, increasing moderate to locally heavy rain showers over these eastern islands. Chances for thunderstorms are also possible for the Big Island on Thursday with this system. Elsewhere, shower activity will trend higher over windward and mountain areas, especially in the overnight to early morning hours. Isolated showers remain in the forecast for most leeward areas. Slight decreasing shower trends are expected from Friday through Saturday as a weak ridge builds in over the islands.
The long range forecast continues to suggest some changes in the weather are on the horizon. Both the American (GFS) and European (ECMWF) show the high pressure ridge north of the islands breaking down as a low pressure system near the Dateline dives south and sets up northwest of Kauai. Easterly trade winds will veer from a more southeasterly direction from Sunday into Monday and shower activity will decrease west of the Big Island due to the rain shadowing effects of southeasterly winds. Deeper tropical moisture with southerly winds in the mid levels may enhance shower activity over Kauai and Oahu around the middle of next week.
Slight changes in this forecast track of this next low pressure system northwest of Kauai next week will produce large changes in rainfall activity, mainly affecting the forecast over the western islands from Kauai to Molokai. Weather model run to run consistency is fairly unsettled on this approaching system, therefore our confidence in the potential for heavy rain threats for any island next week remains low at this time. Stay tuned for weather updates as these island by island rainfall impacts evolve as the forecast time period grows shorter.

Aviation

Moderate to locally breezy trade winds will carry bands of showers off the Pacific towards east and northeast facing slopes and coasts. AIRMET Sierra for mountain obscuration is in effect for northeast Kauai and Oahu as well as windward slopes of the Big island. Conditions are expected to persist through mid-morning. Elsewhere, expect brief periods of MVFR conditions due to lower ceilings and reduced visibility in passing showers.
AIRMET Tango is in effect for both low level and high level turbulence. Occasional moderate turbulence below 8000 feet immediately west through southwest of mountains is the result of the moderate trade wind flow and is expected to persist through 24 hours and beyond. Occasional moderate turbulence above FL250 is the result of a passing upper level jet and is expected to end later this morning.

Marine

A strong high pressure cell located approximately 1,300 miles north northeast of Oahu will remain nearly stationary the next day or so. The downstream pressure gradient created by this high as it slowly meanders east southeast through Friday will result in fresh to locally strong regional trade winds. This morning's ASCAT satellite pass captured the western 2/3rds of the islands and confirmed Small Craft Advisory (SCA) winds through the smaller island bays and channels. While the majority of the nearshore wave energy resides in the short period wind wave spectrum, the recent north northeast swell has allowed what altimetry and buoy data have confirmed to be SCA-level sea state conditions with early morning nearshore seas heights reaching or slightly exceeding 10 feet. Thus, fresh to locally strong trades and/or rough seas will allow the all-water SCA to remain in effect through this afternoon. A new high moving down from the Aleutian Islands will be absorbed into the high northeast of the state Friday. This will subtly weaken trades from Thursday onward. Moderate to locally fresh trades will return early next week.
Recent nearshore buoy observations confirm that Tuesday's 6 to 8 foot north northeast (350-040 degree) swell that peaked surf along north-facing shores yesterday afternoon is on its way down. A small, medium period northwest (320 degree) swell is scheduled to arrive Friday into Saturday. East-facing shores will experience elevated rough wave conditions in response to several days of an upstream fresh trade fetch producing high, short period wind wave chop. East surf at some locations may near High Surf Advisory (HSA) levels later today but many eastern exposures will come in under the 10 foot HSA threshold. Surf along northeastern exposures will remain elevated, as well, as these shores will receive both the fading north northeast swell and east trade wind swell energy. Small, background south swell energy will maintain knee to chest high surf along many southern shores with a small medium period south southwest bump arriving Thursday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters,

Data Courtesy of NOAA.gov