Marine Weather and Tide Forecast for Princeville, HI

DISCUSSION
Latest satellite and radar imagery shows an upper-level cutoff low to the south of the Big Island helping to provide some instability upstream of the state. This is helping to enhance showers moving into windward areas of the islands this morning, embedded within breezy trades generated by a strong surface high to the far northeast.
As we progress through the morning and afternoon hours, expect a slight decrease in shower coverage. However, the possibility for a brief heavy shower or two will still be greater around Maui County and the Big Island today with lingering instability from the low aloft. The kona slopes of the Big Island will also see an increase in low clouds and showers as the sea breeze kicks in.

Breezy trades will hold today before gradually weakening during the first half of the week due to a weak front approaching and passing north of the state, weakening the high northeast of the state. Clouds and showers will remain focused along windward and mauka regions.
The eastern half of the state will still have a good chance for enhanced tradewind showers as the upper level low weakens and shifts north just east of the Big Island Sunday night into Monday. Mid-level ridging will build over the state as the upper low exits the area to the east, creating a gentle, dry and stable tradewind weather pattern through Tuesday.

A strong cold front approaching the state midweek will shift the winds out of the southeast and weaken on Wednesday, becoming light and variable Wednesday night through much of Thursday. This will allow for sea and land breezes to develop, with showers favoring island interiors each afternoon. The front is expected to quickly sweep across the state during the second half the next week.
Depending on the strength and progression of a cold front through the islands Thursday night and Friday, we could see more widespread rain affect the islands, with some heavier showers and even a few thunderstorms not out of the question. In the wake of the front, we will transition back into a typical trade wind regime through next weekend.

AVIATION
Moderate to locally breezy trade winds will bring scattered showers to north through east sections of the islands today, with isolated showers and VFR conditions expected elsewhere. The trades will ease slightly tonight and Monday as an approaching front weakens the ridging north of the islands. Meanwhile, an upper level low is forecast to bring moderate upper level turbulence, with isolated pockets of severe turbulence, over the eastern half of the state from late this morning through the afternoon.

AIRMET Sierra has been issued this morning for tempo mountain obscuration along windward sections of the smaller islands. While shower activity is expected to generally decrease throughout the day, this AIRMET will likely be needed through at least noon.
Additionally, AIRMET Tango remains in effect for low-level mechanical turbulence associated with the breezy trade winds. AIRMET Tango also remains in effect for moderate to isolated severe upper level turbulence from Maui to the Big Island.

MARINE
Surface high pressure far northeast of the state will drive moderate to locally strong trades today before easing overnight.
Trade winds will weaken further on Monday and Tuesday due to a front passing north of the area. The trade winds will become entirely disrupted later in the week when a second cold front is forecast to move through. A Small Craft Advisory (SCA) is currently in effect for the windier waters and channels around Maui and the Big island, but will likely be canceled later this afternoon.

The current moderate long-period northwest swell will peak this evening then taper off. It will be joined on Monday by a larger northwest swell. This second swell will crest Monday night or Tuesday before gradually declining Wednesday through Thursday.
Surf heights could exceed High Surf Advisory (HSA) criteria Monday afternoon through Tuesday night. Towards the end of the week, an even larger northwest will build. This third, and largest swell could bring warning level surf to most north and west facing shores as early as Friday.

Surf along east facing shores will hold relatively steady today, then lower a bit Monday and Tuesday as the trades ease. East shore surf looks to become very small Wednesday and Thursday as the trades become disrupted, with a north swell potentially giving surf a boost to exposed shorelines on Friday.

South shore surf will remain very small through the middle of the week. An out of season long-period south swell may move through the islands at the end of the week, bringing a sizable boost to south shore surf.

FIRE WEATHER
No critical fire weather conditions expected through the forecast period as low-level moisture remains sufficient, with wind speeds remaining below critical thresholds. In addition, a front could bring a period of more widespread rainfall to the islands around the end of the week.

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.