Photo Credit: Tyler Rooke

West Side

Today: Sunny, with a high near 86. East northeast wind 8 to 13 mph.

Tonight: Mostly clear, with a low around 70. East northeast wind 5 to 9 mph.

Tuesday: A 20 percent chance of showers after 11am. Mostly sunny, with a high near 88. East wind around 5 mph.

South Side

Today: Mostly sunny, with a high near 83. Calm wind becoming west southwest around 6 mph.

Tonight: Mostly clear, with a low around 66. Light and variable wind becoming east northeast 6 to 11 mph in the evening.

Tuesday: A 20 percent chance of showers after 11am. Mostly sunny, with a high near 82. East wind 6 to 9 mph.

North Shore

Today: Mostly sunny, with a high near 83. Breezy, with an east wind 16 to 20 mph, with gusts as high as 28 mph.

Tonight: Isolated showers after 8pm. Partly cloudy, with a low around 68. Breezy, with an east wind 10 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 10%.

Tuesday: A 20 percent chance of showers after 11am. Mostly sunny, with a high near 84. Breezy, with an east wind 10 to 17 mph, with gusts as high as 24 mph.

Central Maui

Today: Mostly sunny, with a high near 84. Breezy, with a northeast wind 13 to 17 mph, with gusts as high as 24 mph.

Tonight: Partly cloudy, with a low around 68. East wind 8 to 13 mph.

Tuesday: A 20 percent chance of showers after 11am. Mostly sunny, with a high near 85. Breezy, with an east northeast wind 8 to 16 mph, with gusts as high as 22 mph.

Upcountry

Today: Mostly sunny, with a high near 71. Calm wind becoming west around 5 mph.

Tonight: Partly cloudy, with a low around 54. Light and variable wind becoming east 8 to 13 mph in the evening.

Tuesday: Mostly sunny, with a high near 71. East southeast wind 5 to 10 mph.

East Maui

Today: Scattered showers, mainly after 11am. Partly sunny, with a high near 78. East wind 5 to 9 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 71. East wind 9 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.

Tuesday: Scattered showers, mainly before 11am. Partly sunny, with a high near 79. East southeast wind around 14 mph, with gusts as high as 18 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Lanai City

Today: Mostly sunny, with a high near 76. Northeast wind 9 to 14 mph, with gusts as high as 18 mph.

Tonight: Partly cloudy, with a low around 63. East northeast wind 5 to 9 mph becoming calm.

Tuesday: A 20 percent chance of showers after 11am. Mostly sunny, with a high near 76. East northeast wind around 5 mph becoming west in the morning.

Kaunakakai

Today: Sunny, with a high near 86. East wind 9 to 11 mph.

Tonight: Mostly clear, with a low around 71. Breezy, with an east wind 10 to 15 mph, with gusts as high as 21 mph.

Tuesday: Sunny, with a high near 87. East wind 5 to 11 mph becoming west in the morning.

Detailed Forecast

Synopsis

Breezy trade winds will gradually give way to light and variable winds over the western end of the island chain and light trades elsewhere by Tuesday evening. Trade showers will also be on the decline. The combination of the remnants of a front and a strong surface high pressure system will lead to a wet and windy trade wind regime this coming weekend that all starts on Friday, Christmas Day.

Discussion

A surface ridge is located some 400 miles NW of Kauai this early Monday morning. It will be moving toward the islands at around 10 miles per hour for the next 24 hours. The ridge will stall just N of Kauai Tuesday night before giving way to a new and stronger surface high that will be passing N of the islands between Friday and Saturday. This scenario will lead to trades giving way to light and variable winds over the western islands on Tuesday night and lighter trades across Maui County and the Big Island. The ridge is being pushed toward the island by a front that will dissipate upon reaching Kauai Thursday night. By the time it reaches Oahu sometime on Friday, the front will pretty much be done with.. However, the remnants will continue on to Maui County Friday evening, and on to the Big Island early Saturday morning. Trade winds will return to the western islands Wednesday night while the weakening front approaches Kauai. The trades are expected to start strengthening Thursday as the weakening front closes in on Kauai. Between Thursday night and Friday night, northeast trades will be turning strong and gusty area wide. The strongest trade winds will likely occur on Friday night and Saturday as the 1030 mb surface high passes N of the islands. Models are pointing to very strong and gusty trades, especially the mountain ridges and valleys, the Kohala and saddle areas of the Big Island, Lanai, and Maui’s central valley.
Further more, over the weekend, the remnant moisture from the ex- frontal band is expected to get hung up over the islands. So the combination of these two will lead to a wet and windy trade wind regime. And further more, these showers may get a boost from a passing upper level disturbance resulting in some enhanced or locally heavy trade showers. This entire scenario is subject to change in the coming days. The latest ECMWF run is suggesting a drier weekend, at least for the smaller islands, compared to the GFS version which is much wetter.
In the past few hours, the clouds and showers have loosen up and become less across windward Big Island. Otherwise, shower-bearing clouds are widely spaced upwind of all the islands. Do expect some scattered passing trade showers this morning, favoring the windward and mountain areas. These showers should be becoming isolated by mid or late morning, as per models showing an increasingly more stable air mass throughout today. This stable air mass is expected to hold through Thursday, so that on Tuesday and Wednesday, when sea breezes will be widespread, the showers will be limited to isolated.
We will be paying close attention to the extent of the Kilauea eruption that occurred just before midnight. After a couple of years absence, vog, or volcanic haze, from the latest eruption, could be back as part of the daily forecast. This volcanic haze had been a mainstay for the Kau district and a good part of leeward Big Island from roughly 1983 to up until the summer of 2018. This vog would time to time spill to the other islands, reducing visibility and causing respiratory issues.

Aviation

Fresh trades will continue into early today at which time a gradual weakening trend will commence in response to a weak front encroaching on the area from the north. AIRMET Tango for lee turbulence remains in effect in the meantime. A typical trade wind shower regime will continue through the morning with windward showers occasionally drifting leeward. At this time, nothing more than brief MVFR is expected with this activity.

Marine

A surface ridge about 400 nm N of Kauai will move slowly S as a front approaches from the distant NW, with the ridge expected to be just N of Kauai by tomorrow night. Winds and seas will gradually diminish as this occurs, most notably over Kauai and Oahu waters, while light to moderate E/SE winds linger over portions of Maui and Big Island waters.
In the meantime, moderate to locally strong trade winds persist, warranting a Small Craft Advisory (SCA) for waters around Maui and the Big Island today. Winds and seas will be below SCA criteria statewide from tonight into Wednesday, but an increasing NW swell on Wednesday will likely increase seas to near 10 feet in many areas, warranting a re-issuance of a SCA. Building high pressure to the N will bring increasing NE winds thereafter, driving seas up even further toward the end of the week, with potential for gale-force winds in some of the windier zones.
Moderate WNW swell will continue through Tuesday, maintaining moderate surf along exposed N and W facing shores. A large, long- period NW swell is expected to arrive tomorrow night, peak Wednesday night, and then slowly diminish through Friday. This will likely result in a multi-day High Surf Advisory (HSA) for most N and W facing shores, potentially including the Big Island’s Kona coast.
Out-of-season S swell will build over the next 24-48 hours, with max surf heights on Wednesday getting to the point that a HSA may be required for S facing shores. Rough surf along E facing shores is expected late in the week as NE winds become quite strong, likely requiring a HSA.
The winter solstice occurred at 12:02 AM HST this morning.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov