Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny with isolated showers. Highs 85 to 91 near the shore to around 76 above 3000 feet. North winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 85 to 90 near the shore to around 74 above 3000 feet. Northeast winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 84 to 92. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows around 73. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 83 to 90. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with scattered showers. Highs 75 to 84 in the valleys to around 67 above 4000 feet. Northeast winds up to 10 mph increasing to up to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 90 percent.

Friday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 82 in the valleys to around 65 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 78 to 88. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Occasional showers in the evening, then showers likely after midnight. Lows 66 to 74. East winds 10 to 20 mph. Chance of rain 80 percent.

Friday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 76 to 87. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 76 to 88. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Occasional showers in the evening, then showers likely after midnight. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Friday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 86. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A front approaching the islands from the north will introduce moderate to locally breezy trade winds and increasing shower chances for the western end of the island chain today through Friday as it moves south and then dissipates near Maui County. Light background winds will return and become more southerly from Friday night through the weekend, allowing daytime sea breezes and overnight land breezes to prevail throughout this period. Broad circulation around a low pressure system north of the state could bring enhanced rainfall over portions of the islands early next week.

Discussion

Early this morning, the band of clouds and showers associated with a surface cold front north of the state has become more diffuse as it continues to slowly move south towards Kauai. Latest satellite imagery shows that overnight land breezes have largely diminished cloud cover over the islands and kept showers to a minimum, with little to no rainfall reported across the state since early evening.
The front will continue to slowly sag southward closer to Kauai throughout the day, gradually increasing shower chances and low cloud coverage across the western end of the state. Based on the latest guidance, some minor tweaks were made to the timing of the front's progression, but the overall forecast philosophy remains in tact. The front is expected to move further south down the island chain, reaching Oahu by tonight or early Friday morning. Behind this feature, moderate to locally breezy northeasterly trade winds will build across the western end of the state. The front will likely dissipate on Friday before it reaches the majority of Maui County and the Big Island. Therefore, the eastern end of the state will likely remain in a rather dry land/sea breeze pattern through Friday.
This weekend, another front will approach the state from the northwest. While the main Hawaiian Islands will remain ahead of this feature, winds will become lighter again as it approaches, and the light background flow will veer to become more southeasterly initially on Saturday, then southerly or southwesterly by Saturday night into Sunday. Regardless, the light flow will result in a return of afternoon sea breezes and nighttime land breezes from Friday night into Sunday, especially for the wind-sheltered smaller islands. The general southerly background flow may bring an uptick in showers over some south and southeast facing slopes.
Beyond the weekend, models show a large low pressure system far north of the islands moving southward. The broad circulation around this low could transport enhanced moisture from the tropics into the islands Monday through Tuesday, potentially bringing an increase in showers over the islands, including normally dry leeward areas. Models continue to suggest that the bulk of significant rainfall will remain to the north and west of the main Hawaiian Islands, though there will be potential for deeper tropical moisture to be drawn northward over the eastern end of the state. The potential for enhanced moisture, along with instability from an upper-level trough over the area and daytime heating, could result in afternoon deep convection over interior/leeward Big Island Monday and Tuesday afternoons. While specifics largely remain unknown at this time, details will become more clear over the next several days as the event approaches.

Aviation

Early morning soundings indicate that the island atmosphere is stable, with a strong low-level subsidence inversion based near 6 kft. A shallow cold front about 75 nm N of Kauai is marked by a increasingly diffuse band of showery and stable low clouds, while a surface high pressure cell is centered NNW of the islands. As the high moves E over the next 24 hours, it will push the gradually weakening front over the islands of Kauai and Oahu, bringing an increase in mainly windward showers. Little in the way of upper-level support is expected, so widespread showers are not expected. While trade winds are currently on the lighter side, the high will increase the low-level pressure gradient, leading to increasing trade winds that may become locally breezy by tonight.
There are currently no AIRMETS in effect. Increased shower coverage over windward Kauai may require AIRMET Sierra for tempo mountain obscuration by this afternoon/evening, potentially spreading to Oahu by tonight. AIRMET Tango may be required for low-level turbulence to the lee of the mountains on Kauai and Oahu as trade winds increase.

Marine

Trades will hold in the light to moderate range through Friday for most areas, which will allow localized afternoon sea breezes and overnight land breezes to form near the leeward coasts. The exception will be over the Kauai and Oahu waters tonight through Friday as the tail-end of a weakening front drifts southward into the area, bringing fresh to locally strong trades to the surrounding waters. This will be short-lived due to another front approaching from the northwest, which will lead to a return of light and variable winds by Saturday. Moderate to locally fresh southerly winds are expected Sunday into early next week as this front nears the islands from the northwest.
Surf along exposed north and west facing shores will steadily lower through Friday as a north-northwest swell eases and shifts out of the north. After peaking well above predicted, early morning observations at the offshore NDBC buoys to the northwest reflect this downward trend and are now in decent agreement with guidance (peak spectral energy down into the 12-14 sec bands). This energy extrapolated through the islands supports advisory level surf continuing through much of the day today. Guidance shows this trend continuing through the weekend, with heights dipping below the advisory levels by Friday. Seas should hover just below the Small Craft Advisory level today, then continue to lower Friday into the weekend. A fresh north-northwest swell is forecast to build Sunday night and Monday, with surf potentially nearing advisory levels late Monday through Tuesday for exposed north and west facing shores of the smaller islands.
Surf along south facing shores will hold above the October average into the weekend as a new long-period, south-southwest swell arrives and peaks today through Friday. Surf will ease through the weekend as this swell moves out. An upward trend is expected again early next week with overlapping long-period, south- southwest swells expected. The first one should slowly fill in Monday through Tuesday, with the second and larger one expected Wednesday through the second half of next week.
Surf along east facing shores will remain small today, then pick up tonight through Friday for Kauai and Oahu as a moderate, short-period northeast swell arrives. This will be a short-lived event with a quick drop off expected Saturday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for north and west facing shores of Niihau, Kauai, Oahu, and Molokai, and north facing shores of Maui.

Data Courtesy of NOAA.gov