Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly cloudy. Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs around 85 near the shore to around 73 above 3000 feet. North winds up to 25 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 66 near the shore to around 52 above 3000 feet. Northeast winds up to 15 mph. Gusts up to 35 mph in the evening. Chance of rain 50 percent.

Thursday: Mostly cloudy with showers likely. Highs around 84 near the shore to around 72 above 3000 feet. Light winds. Chance of rain 70 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs around 82. Northeast winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 65. Northeast winds 10 to 20 mph. Chance of rain 30 percent.

Thursday: Mostly cloudy with showers likely. Highs around 81. Northeast winds up to 10 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Cloudy with frequent showers. Locally heavy rainfall possible. Highs 72 to 79 in the valleys to around 63 above 4000 feet. North winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy with frequent showers. Lows 52 to 57 in the valleys to around 47 above 4000 feet. North winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 90 percent.

Thursday: Mostly cloudy with showers likely. Highs 71 to 78 in the valleys to around 62 above 4000 feet. Northwest winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Cloudy with frequent showers. Locally heavy rainfall possible. Highs 75 to 84. North winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with frequent showers. Lows 55 to 65. North winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 80 percent.

Thursday: Mostly cloudy with showers likely. Highs 74 to 83. Northwest winds up to 10 mph in the morning becoming light. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Cloudy with frequent showers. Locally heavy rainfall possible. Highs 75 to 83. North winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with frequent showers. Lows 53 to 67. North winds 10 to 20 mph. Chance of rain 80 percent.

Thursday: Mostly cloudy with showers likely. Highs 74 to 82. North winds up to 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A cold front will move southeastward through Kauai this morning, Oahu this afternoon, then stall out over Maui tonight. A period of strong north winds and showery weather is expected following the frontal passage. This front will weaken into a trough over Thursday morning, then slowly shift westward Thursday afternoon through Friday, with showers favoring the western end of the state. Moderate to locally breezy trade winds and more typical windward and mauka focused showers will return over the weekend and hold in place through early next week.

Discussion

Currently at the surface, a cold front is just off the northwest coast of Kauai and is moving southeastward at 15 miles per hour. Meanwhile, a 1027 mb high is centered to the distant northeast, with ridging extending southwestward to a position a few hundred miles east of Hilo. Strong northerly winds are filling in behind the front, while out ahead of it, land breezes are present in most areas. Infrared satellite imagery shows increasing cloud cover associated with the front upstream of Kauai, with partly cloudy conditions prevail across most of state, aside for windward Big Island where mostly cloudy skies are present. Radar imagery shows numerous showers associated with the front moving towards Kauai, while isolated showers are present near the coast of the other islands. Main short term concern revolves around the progression of the cold front and its associated impacts.
Model guidance remains in good agreement showing the cold front moving through Kauai this morning, Oahu this afternoon, then stalling out and weakening over Maui tonight. Light winds will continue ahead of the front, with land and sea breezes dominant. Behind the front breezy north winds will fill in. The front will weaken into a trough Thursday morning, then retrograde westward Thursday afternoon through Friday. As a result, the winds will diminish on Thursday, becoming light and variable by the afternoon and allowing for sea breeze development in most areas. Moderate southerly flow is then forecast to develop Thursday night, tip southeasterly over the western islands with trades gradually filling in across the eastern end of the state Friday and Friday night. The trades should then return to the western end of the state on Saturday, with with moderate to locally breezy trade winds prevailing Saturday afternoon through the first half of next week.
As for the remaining weather details, the front will bring some widespread showery weather to Kauai today, with the showery conditions expected to overspread Oahu this afternoon. The showery weather will then progress into Maui County tonight, with coverage highest over Molokai. With the strong northerly winds and precipitable water values in excess of 1.5 inches, we will likely see some decent rainfall totals in windward areas, with 1-2 inches certainly possible across north facing sections of Kauai and Oahu. Some localized increase in stream levels and some minor ponding of water seems probable, but no significant flooding is expected. As the front weakens into a trough and shifts westward Thursday through Friday, the shower coverage should be highest over the western half of the state, with drier conditions over the eastern islands. The pattern should transition over to a typical trade wind set up Friday night through early next week, with showers favoring windward slopes and coasts.

Aviation

An advancing cold front over the far northwestern end of the island chain will produce strengthening northerly winds in the vicinity of Kauai this morning. In addition, layered clouds with embedded showers associated with the front will spread across Kauai. The strong northerly winds, clouds and showers will likely reach Oahu by this afternoon. The front will then move over portions of Maui County this evening, where it is expected to eventually stall late tonight. The band of layered clouds and showers will produce periods of MVFR CIGS/VSBYS, especially for north facing slopes, as it moves across each island. Elsewhere, Maui and the Big Island may continue to have weak background winds today. Therefore, clouds and spotty showers may potentially develop as local sea breezes become established over the eastern islands this afternoon.
AIRMET Sierra is being issued for mountain obscuration over north facing slopes of Kauai this morning. This AIRMET may also be needed for Oahu, as well as Molokai, later today or tonight as the front continues moving southeastward. AIRMET Tango will also be issued this morning for Tempo moderate low-level turbulence southwest through southeast of the higher terrain on Kauai. In addition, the upper-level dynamics may require AIRMET Tango to be issued for Tempo moderate clear air turbulence aloft above the western islands later today.

Marine

A front is approaching Kauai early this morning and will reach Oahu this afternoon. Gusty north winds and elevated seas will follow behind the front. A Small Craft Advisory (SCA) is now in effect for waters around Kauai and Oahu, but will likely need to be extended as the front moves over Maui County tonight. The front will weaken to a trough and retreat west Thursday through Friday. Southeast to south winds will develop behind the trough around the eastern waters first then rest of forecast waters. A high will build far north- northeast of the islands early in the weekend, signaling the return of moderate to strong trade winds into early next week.
The anticipated large, short period north swell energy is starting to show up at the far offshore NDBC buoys 51101 and 51001 with swell heights building to 4 to 5 feet between 10 to 14 seconds. This north swell will build down the island chain today bringing advisory level surf to north facing shores of Kauai and Oahu by this afternoon and evening. A High Surf Advisory (HSA) has been issued for north facing shore of Kauai and Oahu through Thursday afternoon. The HSA will likely need to be amended to include other zones later today as the swell is expected to peak locally Thursday then lower Thursday night through Saturday.
A series of moderate, long-period south swells will fill in today through Saturday. With no significant trade wind flow over and upwind of the state, most surf along east facing shores will be from north swell wrap through the week. Moderate, choppy east shore surf will likely return over the weekend and hold into early next week with the returning trades.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Thursday for Niihau, Oahu North Shore, Olomana, Kauai North, Kauai East, Koolau Windward.
Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.
Small Craft Advisory from 6 PM this evening to 6 PM HST Thursday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters.

Data Courtesy of NOAA.gov