Kauai Weather Forecast for August 20, 2023
West Kaua’i
Today: Mostly sunny with isolated showers. Highs 86 to 93 near the shore to around 78 above 3000 feet. Southeast winds around 10 mph. Chance of rain 20 percent.
Tonight: Mostly clear. Isolated showers after midnight. Lows around 73 near the shore to around 63 above 3000 feet. East winds around 10 mph. Chance of rain 20 percent.
Monday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 87 to 93 near the shore to around 79 above 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.
South Kaua’i
Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 85 to 92. Northeast winds 10 to 15 mph. Chance of rain 40 percent.
Tonight: Partly cloudy with scattered showers. Lows 71 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.
Monday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 86 to 92. East winds 10 to 15 mph. Chance of rain 50 percent.
Kaua’i Mountains
Today: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 76 to 85 in the valleys to around 68 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.
Tonight: Breezy. Mostly cloudy with scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.
Monday: Breezy. Partly sunny with scattered showers. Locally heavy rainfall possible in the afternoon. Highs 77 to 86 in the valleys to around 69 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.
North Kaua’i
Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 78 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.
Tonight: Partly cloudy with scattered showers. Lows 67 to 75. East winds 10 to 15 mph. Chance of rain 50 percent.
Monday: Partly sunny with scattered showers. Highs 79 to 90. East winds 10 to 15 mph. Chance of rain 50 percent.
East Kaua’i
Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 89. Northeast winds 10 to 15 mph. Chance of rain 50 percent.
Tonight: Mostly cloudy with scattered showers. Lows 66 to 79. Northeast winds 10 to 15 mph. Chance of rain 50 percent.
Monday: Partly sunny with scattered showers. Highs 78 to 90. East winds 10 to 15 mph. Chance of rain 50 percent.
Detailed Forecast
Synopsis
Moderate trade winds deliver a few clouds and showers to windward areas today, while leeward areas remain mostly dry. Tropical moisture associated the remnants of Fernanda will move over the state on Monday, bringing locally heavy rainfall to windward areas of the Big Island, and potentially Maui County. Windward areas of Oahu and Kauai will also receive some showers. Little significant rainfall is expected over most leeward areas, including leeward Maui. A trend toward breezy and increasingly dry trade wind weather is expected to begin on Tuesday.
Discussion
Satellite imagery shows an overnight increase in low cloud coverage over both windward and leeward waters, with radar indicating a modest increase in shower coverage. A few showers are moving into windward areas, some with small cores of heavier rain, moving too quickly to provide much relief from the recent dry conditions. Model analyses indicate the local increase in low cloud cover is related to the passage of a low-level trough to the N of the islands. Water vapor imagery shows a broad low aloft centered just S of the Big Island, with this feature drifting N toward the islands. The center of the remnant circulation of Tropical Cyclone Fernanda is about 500 miles ESE of Hilo, tracking toward the W near at 15 to 20 mph. The associated field of increased moisture (PWAT > 2″) extends outwards up to 200 miles N of the center, about 300 miles to the E.
The short-term forecast anticipates moderate trade winds that will likely allow localized leeward sea breezes to develop this afternoon. A few showers will move into windward areas, especially this morning, with fewer showers by the afternoon as the effects of the passing surface trough wane. While generally benign weather will prevail today, it looks to be a little cloudier and wetter than the past couple of days, especially windward. Most leeward areas will remain dry, including leeward Maui.
Model guidance continues to indicate that the bulk of the moisture associated with Fernanda's remnant will pass S of the islands from tonight through Tuesday. However, a significant moisture surge is expected over the Big Island and Maui late tonight through Monday, bringing the potential for heavy showers, primarily over windward areas. In addition to the surge in PWAT, the low aloft (and its mid- level reflection) will be located over the islands, providing increased instability due to cooling mid-level temperatures, and divergence aloft as a negatively-trough develops. Simulated satellite imagery depicts a period of deeper convection near and over the Big Island on Monday, thus a slight chance of thunderstorms has been added to the forecast. In addition, the arrival (and temporal extent) of heavy showers over windward Maui has been time shifted to be a bit later as indicated by latest guidance.
Although the potential for heavy rain is fairly high, it should be fairly short-lived, and is not expected to lead to flash flooding. There's a good chance of nuisance-level flooding, but the threat of flash flooding is not great enough to warrant the issuance of a Flood Watch at this time. Anticipated rainfall amounts are lower over Kauai and Oahu as the increase in PWAT is not expected to be as great as that seen farther S. However, dew points rising into the lower 70's will make it feel muggy statewide.
By Tuesday the mid-level low will lift N of the area, and the trough aloft will weaken, allowing stability to increase. This will lead to drier trade wind weather, with building high pressure far NNE of the islands supporting breezy trade winds. Pronounced drying is expected by mid-week as a mid-level ridge develops over the area.
Aviation
Moderate easterly trade winds will continue, with clouds and showers favoring windward and mountain areas. Rainfall chances will trend up over the far eastern end of the state tonight through Monday as an area of deep tropical moisture approaching begins to fill in. This will translate to periods of MVFR CIGS/VSBYS for windward portions of the Big Island and Maui County.
There are currently no AIRMETs, and none are expected through this afternoon. AIRMET Sierra for mountain obscuration will become a possibility tonight into Monday for windward sections of the Big Island and Maui County.
Marine
Surface high pressure far north of the state will maintain moderate to locally fresh trade winds through tonight. As the high builds on Monday, trade winds will strengthen to locally strong speeds with a Small Craft Advisory likely for the windier waters around Maui County and the Big Island. At the same time, the remnants of Fernanda will pass south of the islands, bringing an increase in showers, especially over the windward waters Monday through Tuesday and a slight chance of thunderstorms over the Big Island waters on Monday. High pressure will remain far north of the state through the second half of next week with fresh to locally strong winds persisting.
Surf along east facing shores will remain small through the rest of the weekend due to lighter than normal trades over and upstream of the state. A long-period east swell generated by Hurricane Hilary could bring an increase in surf Monday through the middle of next week. The latest forecast guidance continues to indicate a long- period swell peaking around 3 to 4 feet Tuesday and holding through Wednesday, before quickly lowering through Thursday. Forecast confidence for this swell's details remains low due to its distant source and the compact nature of tropical cyclones. South shore surf will remain small through the weekend. A small, medium-period south to south-southeast swell arriving early next week should produce a modest increase along south facing shores.
HFO Watches/Warnings/Advisories
None.
Data Courtesy of NOAA.gov