Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly cloudy. Isolated showers in the afternoon. Highs around 80 near the shore to around 68 above 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then numerous showers after midnight. Lows around 67 near the shore to around 56 above 3000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 60 percent.

Monday: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs around 80 near the shore to around 68 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

South Kaua’i

Today: Mostly cloudy. Isolated showers in the afternoon. Highs around 79. Northeast winds around 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then numerous showers after midnight. Lows 63 to 68. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 60 percent.

Monday: Cloudy with numerous showers and slight chance of thunderstorms. Highs around 79. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy. Isolated showers in the afternoon. Highs 67 to 75 in the valleys to around 62 above 4000 feet. Light winds. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then numerous showers after midnight. Lows 56 to 61 in the valleys to around 50 above 4000 feet. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 60 percent.

Monday: Cloudy with numerous showers and slight chance of thunderstorms. Highs 67 to 75 in the valleys to around 62 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy. Isolated showers in the afternoon. Highs 72 to 79. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 59 to 68. Light winds. Chance of rain 50 percent.

Monday: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs 72 to 79. Southeast winds up to 10 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly cloudy. Isolated showers in the afternoon. Highs 72 to 79. Light winds. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the evening, then numerous showers after midnight. Lows 57 to 69. Light winds. Chance of rain 60 percent.

Monday: Cloudy with numerous showers and slight chance of thunderstorms. Highs 72 to 79. Southwest winds up to 10 mph shifting to the south in the afternoon. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Mostly dry weather and light winds are expected today, with abundant high clouds continuing to stream overhead. A trend toward muggier and wetter weather is expected to begin tonight, then continue through Monday night, bringing some widespread beneficial rain to most areas. Light to moderate southeast to south winds will develop Monday and Tuesday, with a few locally heavy downpours possible. Shower coverage will be on the decline and sunshine will be on the increase by mid week, with a more typical trade wind weather pattern developing Wednesday night and holding in place through next weekend.

Discussion

Currently at the surface, a trough of low pressure is located around 300 miles south of Honolulu. Meanwhile a 1003 mb low is located to the distant northeast and a cold front to the distant northwest of the islands. The low northeast of the state has effectively cut off the strongest gradient associated with a 1033 mb high well north-northeast of the state, resulting in light trades across the islands, with land breezes present in many area early this morning. Infrared satellite imagery shows considerable high clouds and mostly cloudy conditions across the state. Radar imagery shows a few light showers affecting windward sections of Maui and Molokai, with dry conditions elsewhere. Main short term focus revolves around the potential for some widespread rainfall and some elevated rainfall totals during the next couple days.
The trough of low pressure south of the state will lift steadily northward today. Light background trade winds will prevail today, with sea breezes developing in many areas. Relatively dry conditions will prevail, with a shower or two possible in windward Oahu, Molokai and Maui this morning. Considerable cloud cover will continue to stream over the state, but we could see a shower or two develop over the island interiors this afternoon with the assistance of sea breezes.
Big changes are in store for the local area tonight through Monday night, as we transition out of a cool dry pattern where we've enjoyed dewpoints in the 50s recently, to a humid and wet regime with dewpoints climbing into the 70s. Deep tropical moisture and precipitable water values in excess of 2 inches will overspread the islands tonight through Monday night as the trough moves northward and through the islands. Winds are expected to remain fairly light, but will swing around to the southeast and south during this time. Guidance is in good agreement showing widespread rainfall affecting the islands, although the GFS delays the onset over the smaller islands until Monday, while the ECMWF brings the rain in tonight. Overall, we will show elevated rain chances state wide during the tonight through Monday night time frame, with most areas seeing some beneficial rainfall. Although there could be some locally heavier rain at times, this pattern doesn't appear to be a setup for flash flooding, with abundant cloud cover preventing vigorous deep convective shower development. That said, there remains enough instability that a rumble or two of thunder can't be ruled out statewide on Monday.
Considerable differences continue to plague the extended portion of the forecast, with the GFS advertising continue unsettled weather, while the ECMWF suggests a gradual return toward trade winds. For the moment given the uncertainty, will keep a trade wind pattern reflected in the forecast from Wednesday night onward in favor of the ECMWF. As a result, we expect a light wind regime to hold in place Tuesday through Wednesday, with lingering deep moisture keeping rain chances elevated, although we should see a drop off in shower coverage and a gradual decrease in cloud cover each day. By Wednesday night and continuing into next weekend, we will show a return to more typical trade wind weather pattern with trades holding generally at moderate speeds.

Aviation

Light to moderate winds will deliver low clouds and showers to windward sections of the smaller islands today, occasionally producing MVFR conditions. A band of thick high clouds should move north of the islands, allowing clearer views of low cloud distribution. Little to no shower activity is expected over the Big Island this morning as dry trades veer to southeasterly over the eastern end of the state. Deepening moisture over the Big Island will lead to expanding clouds and showers there this afternoon.
No AIRMETS are in effect now, but AIRMET Sierra may be needed later for mountain obscuration across windward slopes of Maui and Molokai.

Marine

The current large north-northeast swell continues to gradually subside early this morning. However, swell heights are elevated, so combined seas remain 10 feet or greater over waters exposed to this swell. As a result, a Small Craft Advisory (SCA) remains in effect through this afternoon for all Hawaiian waters, except Maalaea Bay. The High Surf Warning (HSW) has been adjusted to a High Surf Advisory (HSA) through early Monday morning for north and east facing shores of most of the smaller islands, while a HSA is now in effect for north and west facing shores of the Big Islands. The HSA has been cancelled for west facing shores of Maui, and north facing shores of Lanai, but surf will likely remain somewhat elevated along those beaches this morning. A Marine Weather Statement is also posted for the potential of moderate to locally strong harbor surges in north facing harbors, especially Hilo and Kahului Harbors. Note that the large north- northeast swell combined with the morning high tide will continue the potential for localized wave runup onto roadways and properties along exposed north and east shores, especially Hilo's Bayfront Highway, for a few more hours this morning.
A surface low pressure system, which is currently about 780 nm north-northeast of Hilo, is moving slowly toward the north- northwest. This feature has caused the pressure gradient to relax across the area, which will keep the background flow relatively weak in the vicinity of the state today. A surface trough lifting up across the state from late tonight through Monday is expected to cause the background flow to shift out of the southeast to south. In addition, enhanced moisture moving up across the state will produce widespread showers and a slight chance of thunderstorm over portions of the coastal waters from late tonight through Monday. Note that there still is some uncertainty in the forecast later this week due to the potential formation of a tropical low far southwest or west of the islands.
The north-northeast swell will continue to gradually subside through Monday. A new long-period west-northwest swell (310 degrees) is forecast to arrive tonight. This swell is expected to gradually increase, with surf approaching the HSA criteria along most north and west facing shores of the smaller islands by Tuesday. This swell is expected to gradually lower from Tuesday night through Wednesday. Another slightly larger west-northwest (310 degrees) swell spreading down across the area Thursday and Friday could produce peak surf heights well above the HSA thresholds along most north and west facing shores. Other than some lingering short-period north-northeast swell energy wrapping into exposed east facing shores during the next few days, surf is expected to be small along most east facing shores later this week. Only minimal background surf is forecast along south facing shores this week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Niihau, Oahu North Shore, Olomana, Maui Windward West, Kohala, Kauai North, Kauai East, Koolau Windward, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters except Maalaea Bay,

Data Courtesy of NOAA.gov