Photo Credit: Tyler Rooke

West Side

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 76 to 84. Light winds. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 72. Southwest winds around 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 73 to 82. North winds 10 to 20 mph. Chance of rain 70 percent.

South Side

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 86. Light winds. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 73. Southwest winds around 10 mph shifting to the northwest after midnight. Chance of rain 30 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 85. Northwest winds 15 to 20 mph. Chance of rain 70 percent.

North Shore

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 76 to 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 69 near the shore to 47 to 54 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 75 to 81 near the shore to around 64 near 5000 feet. Northwest winds 10 to 20 mph. Chance of rain 70 percent.

Central Maui

Today: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 86. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71. Southwest winds around 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 78 to 84. Northwest winds 15 to 20 mph. Chance of rain 70 percent.

Upcountry

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 61 at the visitor center to around 57 at the summit. Southwest winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 47 at the visitor center to around 44 at the summit. West winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 59 at the visitor center to around 55 at the summit. Northwest winds 10 to 20 mph. Chance of rain 70 percent.

East Maui

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 76 to 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 69 near the shore to 47 to 54 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 75 to 81 near the shore to around 64 near 5000 feet. Northwest winds 10 to 20 mph. Chance of rain 70 percent.

Lanai City

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 73 to 80. South winds around 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 63. Southwest winds around 10 mph shifting to the north after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 70 to 78. North winds 10 to 15 mph. Chance of rain 70 percent.

Kaunakakai

Today: Sunny with isolated showers in the morning, then partly sunny with showers likely in the afternoon. Highs 68 to 86. Light winds. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers. Lows 56 to 72. Southwest winds around 10 mph shifting to the north after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 65 to 84. North winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Unsettled weather will persist through the forecast period. An upper low near the Big Island will lift northeastward as a weak surface trough drifts west across the state today. A cold front will move across the island chain Thursday night and Friday, then stall near the Big Island Saturday. Low pressure will drop down toward the state later in the weekend and into early next week, with wet weather expected across portions of the state.

Discussion

Satellite loops show an upper low just southeast of the Big Island and a surface trough extending almost north to south across the Kaiwi Channel. Overnight soundings show a moist and slightly unstable airmass, but light winds near and east of the surface trough axis allowed land breezes to develop from Oahu eastward, keeping these islands mostly clear overnight. Moisture embedded in low level easterly flow west of the trough axis provides fuel for passing showers this morning across Kauai. The upper low will lift off to the northeast today and tonight. The surface trough will linger across the western islands, with scattered showers expected mainly for windward and mauka areas of all islands later today after land breezes collapse.
A front is forecast to reach Kauai Thursday night, then move across the island chain Friday before stalling near the Big Island Friday night and Saturday. The front will be accompanied by a band of showers, and possibly thunderstorms, as it moves down the island chain. Cool northerly flow will fill in behind the front, with showers becoming focused over north facing slopes. Post- frontal winds may be strong enough over Kauai to warrant a Wind Advisory there. Expect showers, and possibly thunderstorms, to continue along the front as it stalls near the Big island. Very strong winds are expected to develop over the Big Island summits by Friday night, then continue into early next week. A High Wind Watch is now in effect for the Big Island summits for Friday night through Sunday night. Snow is expected at the summits as well as the front reaches the Big Island, and a Winter Storm Watch is now in effect from Friday night through Saturday night.
A deep low will drop southward, beginning Friday, to a position just north and west of Kauai over the weekend. Associated instability, along with low level convergence, will increase rainfall chances for a good portion of the state Sunday through Tuesday. However with this type of weather scenario, it is very difficult to pin down impact details. Heavy rainfall will be a threat and shower bands may line up over portions of the state for extended periods of time, increasing the threat for flooding. A Hydrologic Outlook has been reissued for this event, and a Flash Flood Watch will likely be issued as we get closer to onset. Winds will be blowing from the south and southwest later this weekend into early next week. Some areas over and downwind of terrain may see locally gusty winds at times.

Aviation

A northeast to southwest oriented surface trough near Oahu this early Thursday morning will stall out in the Kauai Channel later today. It will remain there until it is absorbed by the cold front slated to reach Kauai early this evening. The front will progress eastward to Oahu around midnight, then on to Maui County early Friday morning. The front is likely to stall near the Big Island Friday.
Except for Kauai, winds will be veering to the south and southwest prior to the front’s arrival. Showers have quieted down across the Big Island, compare to 24 hours ago. The line of heavy showers that formed off the east facing shores at sunset, has dissipated, thanks to a land breeze. A land breeze has formed with most of the other islands as well, resulting in fair skies over land. There is a pool of clouds and showers located in the leeward waters of Oahu and Lanai. A few of the showers are heavy with tops to 25k feet. This area of moisture may affect some of the central islands later today in the form of scattered showers, as the winds turn southerly. AIRMET Sierra for mountain obscuration is a possibility for some of these islands. The front will be ushering in a very strong northerly wind flow to Kauai that will raise AIRMET Tango, commencing with the 04z aviation package. Along with the winds, are the clouds and showers containing IFR ceiling and vis leading to AIRMET Sierra for extensive mountain obscuration.

Marine

A nearly north to south oriented surface trough in the vicinity of the Kaiwi Channel is moving slowly toward the northwest. The close proximity of this feature to the state continues to produce northeast winds over the western islands, and southeast winds over the eastern islands early this morning. Looking ahead, a vigorous cold front is forecast to enter the northwest Hawaiian Offshore Waters by this evening, and then move rapidly down the island chain from late tonight through Friday. This front is expected to stall near, or just east of the Big Island by late Friday. Strong and gusty north to northwest winds and building seas will likely accompany the passage of this front. The surface winds are expected to be strongest over the western end of the state. This has prompted the issuance of a Gale Watch for the potential of gale force conditions developing over the waters surrounding Kauai during the day on Friday. Elsewhere, the arrival of the strong north to northwest winds and a large swell early Friday will boost the seas to 10 feet or higher across most of the Hawaiian waters. Therefore, expect a Small Craft Advisory (SCA) to be issued for most waters east of Kauai starting Friday.
The current small to moderate northwest swell will persist through this evening. Locally generated wind waves plus a building north-northwest swell with a period of 10-11 seconds is expected to start spreading across the area as the front moves down. By late Friday, a very large, medium period north-northwest swell (350 degrees) will likely arrive, and then peak on Saturday. Surf heights produced by this swell will likely be above the High Surf Warning thresholds along most exposed north and west facing shores of the islands. The peak of this swell also appears to coincide with a spring high tide late Saturday night. This could potentially allow localized beach erosion to occur, as well as significant wave runup reaching some coastal areas, including vulnerable low-lying nearshore roadways. In addition to the elevated surf, significant harbor surges are expected along exposed north facing harbors, such as Kahului Harbor.
The stalled surface front is forecast to weaken into a surface trough, and then move westward over the state this weekend. The latest forecast guidance continues to indicate a surface low pressure system will eventually develop west of the state later this weekend. This system, which is described as a Kona Low, will likely bring strengthening southerly winds along with widespread heavy rainfall and the threat of thunderstorms with strong and gusty winds over most of the marine area from Sunday into early next week. In addition, the strong winds and elevated, rough seas will likely continue to require a SCA for most of the coastal waters into early next week.
Expect minimal surf along east facing shores through Friday. Surf is expected to rise along some east facing shores this weekend due to the very large north-northwest swell wrapping into select areas. Surf along south facing shores may rise slightly over the weekend and early next week due to locally generated wind waves produced by the strong south to southwest winds, as well as a series of small background south and southeast swells.

HFO Watches/Warnings/Advisories

High Wind Watch from Friday evening through late Sunday night for Big Island Summits.
Winter Storm Watch from Friday evening through late Saturday night for Big Island Summits.
Gale Watch from Friday morning through Friday afternoon for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.

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Data Courtesy of NOAA.gov