Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny. Haze through the day. Isolated showers in the afternoon. Highs 82 to 87 near the shore to around 75 above 3000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 64 to 70 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs around 84 near the shore to around 74 above 3000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny with isolated showers. Haze. Highs 83 to 88. Light winds becoming east around 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Haze. Lows around 66. Northeast winds around 10 mph.

Tuesday: Mostly sunny with isolated showers. Highs around 84. East winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers. Haze. Highs 75 to 81 in the valleys to around 69 above 4000 feet. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 58 to 65 in the valleys to around 57 above 4000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 20 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 80 in the valleys to around 67 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Haze. Highs 77 to 84. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 60 to 69. Light winds. Chance of rain 20 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 84. East winds around 10 mph. Chance of rain 40 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Haze. Highs 76 to 86. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze. Lows 60 to 71. North winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 84. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Expect light to moderate background east to southeast winds as the high pressure ridge north of the islands remains weak. These lighter winds will allow daytime sea breezes to develop over most islands with a slight increase in clouds and possibly a shower or two over island mountain and interior sections. A cold front moves into the western islands on Wednesday, drifting slowly eastward on Thursday, then spreading enhanced showers into Maui and the Big Island from Friday into the weekend. Moderate to breezy northeast trade winds with this system will boost clouds and showers along windward mountain slopes. A powerful northwest swell will maintain very high surf and will produce coastal impacts along most north and west facing shores today.

Discussion

A weak low level trough passing north of Maui County this morning has not produced much clouds or showers over the eastern islands. Low level southeasterly flow will help produce a rain shadow effect for all smaller islands west of the Big Island. Regional satellite imagery continues to show fairly stable conditions under a building upper level ridge. Upper air balloon soundings this morning as of 2 AM HST from Hilo and Lihue show temperature inversion heights in the 5,000 to 7,000 foot range. These low inversion heights indicate very stable conditions over the region, limiting cloud heights and shower activity.
An upper level ridge will build over the Hawaiian Islands keeping more stable conditions over the region through Tuesday. Trade wind temperature inversion heights aloft will remain in the stable range from 5,000 to 7,000 feet during this time period with only isolated showers possible over each island. The forecast guidance continues to show a cold front moving into Kauai by Wednesday morning with increasing cloud and shower trends spreading eastward to Oahu by Wednesday afternoon and into Molokai and Lanai by Thursday. Moderate to breezy northeast trade winds will build in swiftly as the frontal cloud band passes each island.
By Friday, a high pressure system moving into the Central Pacific region will help push the clouds along the dissipating frontal boundary further eastward into Maui and the Big Island from Thursday night into Friday. A combination of northeast trade winds, an upper level trough digging in from the north and unstable clouds along the weakening frontal boundary will bring periods of showers and decent rainfall amounts to windward slopes of both Maui and the Big Island from Friday into the weekend. Drying trends are forecast for the western islands during this time period under a building ridge aloft.
Global forecast models are in good agreement that this rainfall will reach the eastern half of the state by Friday morning as the high pressure system building in behind the front shows a strong west to east progression. There is the potential for periods of heavy rain over windward Maui and the Big Island in this weather pattern set up. Stay tuned for more wet weather details this coming week as the forecast time period shortens and our confidence in island by island impacts improves.

Aviation

Light to moderate east southeast flow will continue. Ragged bands of weak cumulus will favor north and east facing coasts through mid-morning. Light sea breezes along leeward coasts in the afternoon will help to focus cloud cover over island interiors that will persist through the evening hours. Shower activity is expected to remain minimal through midday, but locally moderate showers are likely over inland portions of the Big Island late afternoon through early evening. Brief MVFR CIG and VIS are to be expected in showers, otherwise VFR conditions will prevail all areas.
No AIRMETs are in effect or anticipated at this time.

Marine

A powerful NW (320 degrees) swell will continue to bring extra large surf, and the potential for coastal impacts today as it gradually diminishes from NW to SE across the island chain. Latest buoy observations of significant wave height at NDBC buoys 51001/51101 NW of Kauai indicate a gradual decrease in wave height overnight, with average wave heights running about 16-18 feet. An early morning high tide will bring potential for coastal impacts statewide due to wave runup today, with special concerns for coastal roadways/homes/businesses along W facing shores of the Big Island, where the swell's peak will closely coincide with the high tide.
A High Surf Warning (HSW) remains posted today for N and W facing shores most exposed to the swell, while a High Surf Advisory (HSA) is in effect for W facing shores that are less exposed. See the Coastal Hazard Message (CFWHFO) for additional details. With the swell as large as it is, some energy will wrap into select breaks along S facing shores. A Marine Weather Statement (MWSHFO) is also posted to alert boaters to the potential for waves breaking in and near harbor entrances, among other marine hazards.
This swell will gradually diminish into Tuesday, but a new large NW (320 degrees) swell is expected to arrive Tuesday night and Wednesday. Although not expected to be as impactful as the current swell, peak surf heights will likely be large enough on Wednesday to prompt a HSW for exposed N and W facing shores. This next swell will gradually diminish Thursday into Friday, with the long-range outlook featuring a moderate-size WNW swell next weekend, with potential for a N swell as well.
A Small Craft Advisory (SCA) remains posted for virtually all zones through tonight for seas greater than 10 feet. Seas will briefly diminish below SCA heights Tuesday, but seas with the next NW swell will be large enough to require a SCA, especially since locally strong NE winds are expected to develop. High pressure building NW of the islands from Wednesday into Friday will push a cold front from NW to SE down the island chain, while also supporting fresh to strong NE trade winds. In the meantime, a surface ridge just N of the islands will support light to moderate E-SE winds through Tuesday, with winds lightest on the W end of the island chain.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST this evening for north and west facing shores of Niihau, Kauai, Oahu, Molokai, north facing shores of Maui, and west facing shores of the Big Island..
High Surf Advisory until 6 PM HST this evening for Maui Leeward West, Lanai Leeward.
Small Craft Advisory until 6 AM HST Tuesday for all Hawaiian waters except Maalaea Bay.

Data Courtesy of NOAA.gov