Photo Credit: Jeni Ji Cousins

West Side

Today: Breezy. Partly sunny with scattered showers and slight chance of thunderstorms. Highs around 79. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 62 to 70. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 80. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

South Side

Today: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 79. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 63. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy with scattered showers. Highs around 80. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

North Shore

Today: Cloudy with frequent showers and slight chance of thunderstorms. Highs around 79 near the shore to around 68 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tonight: Cloudy with frequent showers and slight chance of thunderstorms. Lows 60 to 68 near the shore to around 48 near 5000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Saturday: Cloudy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 80 near the shore to around 68 near 5000 feet. Northeast winds around 10 mph. Chance of rain 90 percent.

Central Maui

Today: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs around 79. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows 61 to 66. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Cloudy with numerous showers and slight chance of thunderstorms. Highs around 80. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Upcountry

Today: Cloudy with scattered showers and slight chance of thunderstorms. Highs around 58 at the visitor center to around 48 at the summit. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered rain showers and slight chance of thunderstorms. Lows around 41 at the visitor center to around 34 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy with scattered rain showers and slight chance of thunderstorms. Highs around 58 at the visitor center to around 48 at the summit. Northeast winds around 10 mph. Chance of rain 50 percent.

East Maui

Today: Cloudy with frequent showers and slight chance of thunderstorms. Highs around 79 near the shore to around 68 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tonight: Cloudy with frequent showers and slight chance of thunderstorms. Lows 60 to 68 near the shore to around 48 near 5000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Saturday: Cloudy. Frequent showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs around 80 near the shore to around 68 near 5000 feet. Northeast winds around 10 mph. Chance of rain 90 percent.

Lanai City

Today: Breezy. Partly sunny with scattered showers. Highs 72 to 78. Northeast winds around 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 63. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs 72 to 78. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaunakakai

Today: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 76 to 82. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 56 to 70. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs 76 to 82. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Cool, dry and breezy northeast trade winds will continue over Kauai and Oahu through early Saturday, as cloudy and locally wet conditions persist near a dissipating front over the Big Island and Maui County. A trough, remnants of the front, will linger over the island chain during the weekend and possibly Monday, bringing strong northeast trade winds to Kauai and Oahu. A disturbance aloft will increase the potential for locally heavy rainfall late Saturday and Sunday.

Discussion

A stalled front is focusing showers across windward slopes of northern Big Island and Maui County, while cool, dry, and stable conditions persist over Oahu and Kauai. Meanwhile, a sharp upper level trough is generating thick layered clouds across the Big Island and Maui and is maintaining enough instability to trigger a few thunderstorms along the front on northern Big Island. The heaviest showers have been occurring in remote portions of the Kohala mountains, and numerous gages on the Hamakua Coast, North Kohala District and windward Maui have measured over a half inch of rainfall during the past six hours, while the West Wailuaiki station has picked up over two inches. In a sharp contrast, the breezy northeasterly flow in place across Oahu and Kauai has produced no rainfall, and dew points in the mid to upper 50s are maintaining a cool feel.
Expect little change through tonight as the front weakens to a surface trough and the upper level trough broadens and slowly weakens. The focus for rainfall should remain along the surface trough, maintaining higher rain chances and the possibility of thunderstorms along windward slopes of northern Big Island and Maui County. Interior sections of the Big Island may experience an afternoon heavy shower or thunderstorm, though high clouds blanketing the eastern half of the island chain may inhibit convection. In addition, the high summits of the Big Island could see snow showers, mainly in the afternoon. On Oahu and Kauai, expect morning windward clouds to deliver no rainfall and to largely burn off by mid morning. Dew points may creep up as the air modifies tonight, but chances for showers will remain very low.
For Saturday, the surface trough will drift westward as upper level trough begins to deepen west of the state. Wet conditions will hold across windward Maui County and should shift back to windward Oahu. The deepening upper level trough will generate more widespread high clouds and may trigger a few thunderstorms across the wetter windward areas. Interior Big Island could also see a few afternoon thunderstorms and summit snow showers as well. Over on Kauai, drier conditions will persist.
Saturday night into Monday, chances for heavy rainfall and thunderstorms increase, but the details remain uncertain. The GFS and ECMWF model both sharpen the upper level trough just west of Kauai Saturday night and produce a compact upper level low to the southwest of the state Sunday. This will lead to mid level ascent that will thicken high clouds over the island chain and produce moist and unstable conditions. The GFS continues to produce what appears to be a spurious surface low over the state, and the more believable ECMWF solution draws ample moisture over the Big Island, while the lingering surface trough continues to feed low level moisture over windward slopes of Maui County and Oahu, and perhaps to Kauai be late Sunday. Due to ongoing model inconsistencies, confidence is not sufficiently high for the issuance of any flood related headlines at this time. There is increased confidence that the sharpening low level trough will lead to strengthening northeasterly trade winds over Kauai and Oahu on Sunday.
Though wet conditions will likely linger into Monday, the GFS and ECMWF show the upper level low drifting away from the state to the southwest, suggesting that chances for heavy rainfall will decrease as high clouds thin. Breezy east to northeast winds will persist, focusing the bulk of the shower activity over windward areas.
Beyond Monday, the forecast favors trade winds, but the uncertainty remains unusually high regarding rainfall. The longwave pattern points toward lingering upper level troughing, suggesting that we could see another day or two of active showers.

Aviation

Dry and stable conditions, with limited showers, will persist across Kauai and Oahu through today. Increased moisture and instability east of Oahu associated with a stalled front will continue to generate low clouds and showers, especially across windward slopes of Maui county and the Big Island. Expect MVFR conditions in low clouds and showers, with potential IFR conditions as well. AIRMET Sierra is in effect for this and will be updated as conditions warrant.
Models and a lack of reports show that earlier turbulence has eased, allowing expiration of AIRMET Tango. Neither AIRMETS Tango nor Zulu, for icing, are expected through today.

Marine

A front over the southeast waters will linger over the eastern part of the state as it becomes a trough later today. This feature will continue to produce periods of showers and isolated thunderstorms around Maui County and the Big Island. Moderate to locally strong northeast winds will strengthen today as a high builds northwest of the state. Over the weekend a stronger high will build northwest of the state, and a trough over or near the state will sharpen the gradient, strengthening northeast trades to strong to near gale speeds over the western half of the state by Sunday. A Small Craft Advisory (SCA) is currently in effect due to the combination of high seas and locally strong winds for most zones through today. The SCA will need to be readjusted as seas drop below 10 feet throughout the day.
As the current (310-320 degree) northwest swell fades, a series of moderate north swells will move through today into the first half of next week. These north swells will keep surf elevated, especially along north facing shores. A new long period moderate northwest swell (310 degree) is expected to boost surf heights back to High Surf Advisory levels along north and west facing shores Sunday into Monday. Surf along east facing shores should see wrap from the north to northwest swells through early next week. Elsewhere, small surf remains in the forecast for south facing shores into early next week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Friday for north facing shores of Niihau, Kauai, Oahu, Molokai, and Maui.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters.

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Data Courtesy of NOAA.gov