West Kaua’i

Tonight: Mostly clear. Lows 69 to 74 near the shore to around 62 above 3000 feet. Light winds.

Monday: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 85 to 92 near the shore to around 77 above 3000 feet. Light winds. Chance of rain 40 percent.

Monday Night: Partly cloudy with isolated showers. Lows 71 to 76 near the shore to around 63 above 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly clear. Lows around 73. Northeast winds around 10 mph.

Monday: Mostly sunny with isolated showers. Highs 82 to 90. East winds around 10 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 75. Northeast winds around 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 67 in the valleys to around 59 above 4000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 84 in the valleys to around 68 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows 66 to 74. East winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 87. East winds up to 10 mph. Chance of rain 40 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 66 to 75. East winds around 10 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows 64 to 77. Northeast winds around 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs 75 to 88. East winds around 10 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 66 to 78. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate trade winds will prevail through Monday as a shallow area of moisture brings increased humidity and higher shower chances to the central then western end of the island chain. Locally breezy trade winds and rather dry conditions will develop on Tuesday and Wednesday and will likely persist into next weekend.

Discussion

Gentle to locally moderate trade winds continue to push an area of shallow moisture over portions of the island chain. The trough associated with the moisture has largely dissipated over the islands but is strong enough to the north to ease the local pressure gradient and keep trades lighter than normal. The trough dropped up to a half of an inch of rainfall on windward Big Island last night and has produced scattered showers on windward Maui County today. Leeward and interior Big Island are experiencing scattered showers this afternoon, and the moisture was deep enough to trigger a few thunderstorms on the higher elevations of Mauna Loa. Dew points on these islands have also been elevated in the low 70s, leading to a humid feel. Meanwhile, fewer showers and lower humidity have prevailed on Oahu and Kauai.
The area of moisture will creep westward to Oahu tonight and Kauai on Monday. Humid conditions will develop on these islands as dew points climb into the lower 70s, and while rainfall from windward shower activity is not expected to be significant, daytime sea breezes could trigger isolated briefly heavy leeward showers Monday afternoon. Meanwhile, drier conditions will slowly filter in on Big Island then Maui County, even though dew points remaining in the upper 60s. Minimal windward showers are due over the eastern end of the state, mainly windward, though the Kona slopes of the Big Island may experience scattered afternoon showers.
Trade winds will gradually strengthen Tuesday and Wednesday as drier conditions develop. Even though a surface trough will linger north of the state, Tropical Depression One-C (which is forecast to become a tropical storm) passing well south of Hawaii will help tighten the local pressure gradient and drive stronger trades. There is still a bit of uncertainty as to how strong the trades will get, but the latest guidance suggests locally breezy winds will develop late Tuesday and be slightly stronger Wednesday. Ridging aloft will strengthen during this time, bringing a lower inversion that could contribute to gusty conditions on Wednesday. Under these stable conditions, only modest windward rainfall is expected, with dry weather favored leeward.
Moderate to locally breezy trade winds will persist into next weekend as surface high pressure holds north and northeast of the state. Relatively dry trade wind weather is expected.

Aviation

Gentle trade winds with localized areas of nighttime land and daytime sea breezes tonight into Monday as a surface trough tracks west from near Maui to Kauai through the next 24 hours.
There are currently no AIRMETs in effect, but AIRMET Sierra for mountain obscurations could be possible over windward areas of Maui County amd Oahu overnight with the upstream clouds and showers.

Marine

High pressure far northwest of the state will slowly build north of the area throughout the week. Trade winds will maintain gentle to locally fresh speeds through Monday then strengthen Tuesday into Wednesday to moderate to locally strong levels. As the trades strengthen, a Small Craft Advisory for the windier waters and channels around Maui County and the Big Island is expected by Tuesday or Wednesday. Trade winds could strengthen further by the end of the week, which could cause the expansion of the Small Craft Advisory to other coastal water zones.
Tropical Depression 01C located far southeast of the Big Island is expected to pass far south of the state as a tropical storm around the middle of the week. Minimal impacts are expected, but some moderate southeast swells will be possible. Over the offshore waters, Tropical Depression 01C could bring some isolated thunderstorms for the far southern areas of the offshore waters. For more info, please check the public advisories on Tropical Depression One-C under WMO header WTPA31 PHFO and under AWIPS header HFOTCPCP1. Forecast/Advisories on Tropical Depression One-C are issued under WMO header WTPA21 PHFO and under AWIPS header HFOTCMCP1.
South facing shores will remain small the next few days with mainly background energy. A storm force low east of New Zealand last week Wednesday (7/23) will send a moderate long-period south swell, which should be filling in as early as Tuesday. This initial south swell should peak on Wednesday near or slightly above the summer average. A much stronger hurricane force low developed southeast of New Zealand on Thursday (7/24) and tracked northward while gradually weakening through today. This low should send a long-lived south swell with forerunners arriving as early as Wednesday and steadily building through Thursday. This swell will likely peak late Thursday into Friday at High Surf Advisory thresholds and gradually fade over the weekend into early next week.
East facing shores will remain small through Monday before slowly rising Tuesday through the rest of the week as trade winds increase. Southeast swell from Tropical Depression One-C will also be possible during the second half of the week. Flat summer time surf will continue along north facing shores this week. An out of season small long-period northwest swell will be possible late next weekend from Typhoon Krosa currently located in the western Pacific.

Fire weather

Trade winds will remain weaker than normal and dew points will remain elevated over portions of the state through Monday, mitigating fire weather concerns. A rather dry, stable, and locally breezy trade wind flow will develop late Tuesday or Wednesday. A tropical cyclone passing well south of Hawaii during this time is producing some uncertainty in the strength of the winds for Wednesday, but near critical conditions are possible, with elevated fire weather concerns persisting into next weekend.

HFO Watches/Warnings/Advisories

None.

Kauai Now Weather is brought to you by Blue Hawaiian Helicopters.