Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny, with a high near 87. Light and variable wind becoming east around 5 mph in the afternoon.

Tonight: Isolated showers after 9pm. Partly cloudy, with a low around 66. Calm wind. Chance of precipitation is 20%.

Sunday: Scattered showers, mainly after 7am. Partly sunny, with a high near 83. Calm wind becoming west 5 to 7 mph in the afternoon. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

South Side

Today: Isolated showers after 2pm. Increasing clouds, with a high near 87. Northeast wind around 5 mph becoming calm. Chance of precipitation is 20%.

Tonight: Isolated showers before 9pm. Partly cloudy, with a low around 64. Light and variable wind. Chance of precipitation is 20%.

Sunday: Scattered showers after 7am. Partly sunny, with a high near 83. Calm wind becoming west 5 to 7 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

North Shore

Today: Mostly sunny, with a high near 85. Windy, with a northeast wind 8 to 13 mph increasing to 18 to 23 mph in the afternoon. Winds could gust as high as 33 mph.

Tonight: Isolated showers after 9pm. Partly cloudy, with a low around 65. Northeast wind 8 to 13 mph becoming light and variable after midnight. Chance of precipitation is 20%.

Sunday: Scattered showers, mainly after 7am. Partly sunny, with a high near 81. Calm wind becoming north northwest around 6 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Central Maui

Today: Mostly sunny, with a high near 85. Breezy, with a light north northeast wind becoming northeast 13 to 18 mph in the morning. Winds could gust as high as 26 mph.

Tonight: Isolated showers after 8pm. Partly cloudy, with a low around 63. North northeast wind around 5 mph becoming calm in the evening. Chance of precipitation is 20%.

Sunday: Scattered showers. Partly sunny, with a high near 81. Calm wind becoming north northeast around 6 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Upcountry

Today: Mostly sunny, with a high near 73. Calm wind becoming west northwest around 6 mph.

Tonight: Mostly clear, with a low around 54. Calm wind.

Sunday: Scattered showers. Partly sunny, with a high near 69. Calm wind becoming west 5 to 9 mph in the morning. Chance of precipitation is 30%. New precipitation amounts between a quarter and half of an inch possible.

East Maui

Today: Scattered showers. Mostly cloudy, with a high near 83. East southeast wind 5 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 61. South southeast wind 5 to 11 mph becoming west southwest after midnight. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Scattered showers. Partly sunny, with a high near 79. South southeast wind 5 to 9 mph becoming calm in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Lanai City

Today: Scattered showers after 1pm. Increasing clouds, with a high near 76. Calm wind becoming west northwest around 5 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers before 8pm. Cloudy during the early evening, then becoming partly cloudy, with a low around 64. West southwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Scattered showers. Partly sunny, with a high near 74. Light and variable wind becoming northwest 5 to 10 mph in the afternoon. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Kaunakakai

Today: Mostly sunny, with a high near 82. Southeast wind 5 to 8 mph becoming calm in the afternoon.

Tonight: Partly cloudy, with a low around 67. Calm wind.

Sunday: Scattered showers. Partly sunny, with a high near 79. Calm wind becoming west northwest around 6 mph in the afternoon. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Detailed Forecast

Synopsis

Light to moderate trade winds will continue today with clouds and showers favoring windward and mountain areas. Rainfall chances will quickly rise through the day Sunday as the winds shift out of the south to southwest ahead of a strong cold front approaching. This front will quickly advance down the island chain Sunday night, then stall around the Big Island Monday through Tuesday. Heavy showers and a few thunderstorms will be possible along ahead of this front. Cool and gusty northerly winds are expected following the frontal passage over the western end of the state early next week. Trade winds may return late next week.

Discussion

Short-term guidance has initialized well with the current pattern and depicts mostly dry conditions with light to moderate trade winds continuing across much of the area today. The exception will be over and around Kauai where showery conditions will remain possible due to a trough nearby.
A transition period is expected tonight through Sunday as a cold front associated with a gale currently north of Midway approaches. Low-level winds will quickly shift out of the south and southwest ahead of this approaching boundary – potentially increasing to moderate levels over and around Kauai/Oahu later Sunday. Increasing instability and lift out ahead of this front and its attendant shortwave trough aloft will be enough to trigger spotty pre-frontal showers Sunday afternoon over Kauai and Oahu.
The cold front is forecast to reach Kauai late Sunday, then move down the island chain Sunday night through Monday. Model reflectivities are in decent agreement and depict the leading edge of the main line of showers along the front reaching Kauai late Sunday afternoon, then to Oahu and Maui County Sunday night. Lowering upper heights combined with 40-50 kt 0-6 km shear ahead of this upper trough will support a few thunderstorms Sunday night into Monday. The one limiting factor with regard to the strength of these storms could be the phasing between the upper trough and deep moisture axis along the front (appears to be a lag in the latest model cycle). If these were to align, a few strong storms can’t be ruled out – especially over the coastal waters Sunday night.
Gusty northerly winds (potentially reaching advisory levels beginning Sunday night) and cool conditions will follow the frontal passage across the western end of the state early next week. Guidance reflects this and depicts dewpoints dipping into the 50s for Kauai and Oahu.
There remains subtle differences in the global models on how far east the front will progress before stalling. The GFS moves the front to just east of the Big Island on Tuesday while the ECMWF has the front stalling over the Big Island. Either way, the Big Island and possibly east Maui will remain rather wet on into Wednesday, which could result in localized flooding concerns.
Winter weather conditions can’t be ruled out over the Big Island summits Monday night into midweek due to a combination of the deep moisture axis associated with the front hanging up or stalling and cold temperatures aloft arriving with the shortwave trough.
As we head on into Thursday, high pressure will build in northeast of the area resulting in strengthening trade winds. Moisture associated with the frontal boundary is then forecast to move back westward likely providing for a wet trade wind pattern to set up across the state. With the differences in the long range models continuing, changes to the forecast our possible next week.

Aviation

A weak surface trough has stalled northwest of Kauai, and its influence on the weather over Hawaii is diminishing early this morning. Light to moderate low-level trade winds appear to be filling in across most of the state, including Kauai. The trade winds will deliver low clouds and isolated showers along some of the windward coasts and slopes of the islands this morning. The trade winds are expected to remain weak enough to allow local afternoon sea breezes to become established over most islands. These sea breezes may cause low clouds and a chance of showers to develop over the interior sections of some of the islands later today. Brief periods of MVFR conditions may occur along some windward sections of the state this morning, and across the interior terrain of some of the islands this afternoon. Otherwise, expect primarily VFR conditions to prevail across the state today.
As we head into this evening, local nighttime land breezes may again develop over most islands. However, later tonight and Sunday, the winds will begin to shift out of the southwest, and gradually strengthen as a strong cold front approaches the region from the northwest. The strengthening southwesterly winds may start to bring increasing cloud cover and showers up toward Kauai by early Sunday.
No AIRMETs are currently in effect, and none are anticipated through this evening.

Marine

In summary, an active winter pattern this holiday weekend, with giant surf today and tonight, and a potent cold front moving down the island chain late Sunday into Monday.
The largest NW swell of the winter season so far will rapidly build through the day, with peak surf heights of 40 to 50 feet (with locally higher waves) expected along exposed shores, where a High Surf Warning is in effect. Based on overnight observations from offshore NDBC buoys 51001/51101 NW of Kauai (now at 19 feet 19 seconds), the expectation is that the peak of the swell will occur on Kauai around late morning, on Oahu shortly after mid- day, and mid- to late-afternoon on Maui. A High Surf Advisory has been issued for exposed N and W facing shores of the Big Island for surf building this afternoon, and peaking overnight. The swell will gradually diminish from NW to SE on Sunday and Sunday night, but a new NW swell arriving into Monday will likely push surf to warning levels once again, with peak surf heights lower than today’s swell.
The giant NW swell, and today’s increased E/SE winds, have prompted a Small Craft Advisory for all waters as seas build rapidly, and a Marine Weather Statement due to the potential for surges and significant wave action in and near exposed harbors. Due to the period and size of the NW swell, some (much reduced) swell may wrap into select S and E facing shores.
A surface ridge N of Kauai has strengthened overnight, while a trough NW of Kauai has all but dissipated, leading to increased E to SE winds, with locally strong winds expected through this afternoon over some Maui and Big Island waters. The ridge will move back S (and over the islands) tonight as what is expected to be a vigorous cold front rapidly approaches from the NW. This front will force the ridge to move SE of the Big Island Sunday and Sunday night, leading to a brief period of light to moderate S to SW winds, until the front’s passage ushers in near gale force N winds Sunday night. A strong high to the NW of the islands will continue to support strong to near-gale force NE winds over most waters into Monday as the front stalls over the eastern islands. As the front stalls, it will continue to act as a focus for shower development as it transitions to a trough, and then moves back toward the smaller islands as trade winds gradually return Tuesday and Wednesday.
The front will initially bring the potential for locally heavy showers and maybe a thunderstorm as it moves relatively quickly through Kauai and Oahu, and then slows over Maui County and the Big Island. A strong trough aloft is expected Monday and Tuesday, maintaining (and maybe even increasing) the potential for heavy showers and thunderstorms along the boundary.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 AM HST Sunday for Niihau, Kauai Windward, Kauai Leeward, Waianae Coast, Oahu North Shore, Oahu Koolau, Olomana, Molokai, Maui Windward West, Maui Central Valley, Windward Haleakala.
High Surf Advisory from noon today to 6 PM HST Sunday for Kona, Big Island North and East, Kohala.
Small Craft Advisory until 6 PM HST Sunday for all Hawaiian waters except Maalaea Bay,
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay.

Data Courtesy of NOAA.gov