West Kaua’i

Tonight: Partly cloudy. Scattered showers in the evening. Lows 71 to 76 near the shore to around 62 above 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny with isolated showers. Highs around 89 near the shore to around 77 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Tuesday Night: Mostly clear. Lows 72 to 77 near the shore to around 62 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 71 to 76. Northeast winds around 10 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 90. East winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 72 to 77. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 67 to 72 in the valleys to around 60 above 4000 feet. East winds around 10 mph. Chance of rain 70 percent.

Tuesday: Partly sunny with scattered showers. Highs 76 to 88 in the valleys to around 68 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 68 to 73 in the valleys to around 61 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Lows 66 to 75. East winds around 10 mph. Chance of rain 70 percent.

Tuesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 89. East winds 10 to 15 mph. Chance of rain 30 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows 67 to 76. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 67 to 78. East winds around 10 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 68 to 79. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate trades will strengthen over the next couple of days to moderate to locally strong as a high north of the state builds. Clouds and showers will focus along windward and mauka areas, particularly overnight and early morning as a rather dry and stable airmass settles over the state and persists into next weekend.

Discussion

Afternoon satellite and radar imagery show clouds and showers over and along leeward and interior areas due to afternoon sea breezes, in addition to clouds and showers along windward and mauka areas under a light to moderate trade wind flow. The higher elevations of Mauna Loa on the Big Island is also experiencing some isolated thunderstorms with locally heavy showers. High resolution model guidance is still on track with trade winds strengthening tonight into Tuesday to moderate to locally breezy as a high north of the state strengthens. Expect increasing clouds and scattered to numerous showers to focus mainly along windward and mauka areas, particularly around Kauai as low-level moisture lingers into Tuesday.
Tuesday afternoon, mid- level ridging should provide more stability around the state, thus did not put thunder in the forecast for the upper slopes of the Big Island Tuesday afternoon. Low- level moisture should return to near summertime normal with typically scattered clouds and showers mainly focusing along windward and mauka areas during the overnight and early morning hours. This pattern is expected to continue into the weekend as the surface high remains anchored north of the state.
Tropical cyclone activity continues to heat up far south and southeast of the Hawaiian Islands as Tropical Storm Iona has now been upgraded to Hurricane Iona and Tropical Depression 2C has now been upgraded to Tropical Storm Keli. There is also third area the National Hurricane Center (NHC) is tracking for tropical cyclone development east of Keli. The track of all three systems will likely continue to drift westward, passing far south of the Hawaiian Islands through the rest of the week based on NHC advisories and global model forecasts. There is currently no immediate threat to the main Hawaiian Islands from these systems. We will continue to monitor these tropical systems as they pass far south of the state for potential in lowering inversion heights, and limiting clouds and showers Wednesday into the weekend.

Aviation

Trade wind pattern today will continue into tomorrow with showers focused on the windward and mtn areas. Prevailing VFR to isolated MVFR conditions are possible. There will likely be some lower clouds tonight that could cause isolated mtn obsc. No airmets currently in effect.

Marine

The current gentle to moderate trade wind flow will gradually build to fresh to locally strong levels on Tuesday and Wednesday. Trades will increase as a weak surface trough dissipates near the islands. This will allow the pressure gradient to tighten locally as high pressure to the far northwest drifts southeastward and Hurricane Iona and Tropical Storm Kali pass several hundred miles south of the state. A Small Craft Advisory (SCA) goes into effect tonight for the typically windy waters around the Big island and Maui County, and the SCA expands to the Kaiwi Channel and all waters around the Big Island and Maui for Tuesday and Wednesday. The fresh to strong trades and the SCA will likely persist through the weekend.
Although the tropical cyclones are forecast to pass several hundred miles south of Hawaii over the next couple of days, more information on Hurricane Iona can be found at WMO header WTPA21 PHFO and AWIPS header HFOTCMCP1, and information on Tropical Storm Keli can be found at WMO header WTPA22 PHFO and AWIPS header HFOTCMCP2. Isolated thunderstorms along the northern periphery of these systems may effect the far southern portion of the offshore waters, and while some short-period southeast swells may reach southern shores of Hawaii, a much larger and unrelated south swell will dominate.
An active period of south swell is due this week. The first in a series of long-period swells will arrive late Tuesday afternoon or evening and will push south shore surf to summertime average on Wednesday. Long-period forerunners of a much larger swell, which built through the day at the PacIOOS Aunuu buoy off of American Samoa, will overlap the first swell on Wednesday, and the bulk of the swell will peak at 4 to 5 feet in Hawaiian waters on Thursday, producing surf in excess of the High Surf Advisory threshold through Friday. The swell will gradually decline over the weekend and will be followed by another sizable south swell early next week.
East shore surf will trend up over the next few days as strengthening trade winds generate larger wind waves. Surf along east facing shores will rise to seasonal average late Wednesday or Thursday and hold into the weekend, followed by a likely decline early next week.
Flat summer conditions along north facing shores may be interrupted this weekend by a small long-period northwest swell from Typhoon Krosa, currently in the western Pacific.

Fire weather

Expect higher humidity levels to gradually lower to more typical summertime levels through Tuesday as a drier and more stable airmass builds over the state. Humidity and wind speeds will near critical conditions Wednesday into the weekend as breezy conditions develop. Some uncertainty remains in the wind speeds later this week and will continue to monitor for possibility of any headlines.

HFO Watches/Warnings/Advisories

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

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