Photo Credit: Braden Jarvis

West Kaua’i

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South Kaua’i

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Kaua’i Mountains

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North Kaua’i

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East Kaua’i

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Detailed Forecast

Synopsis

Trades will continue to strengthen today with gusts up to 50 mph possible over the windiest portions of Maui county and the Big Island. A dissipating front will bring increasing showers to Kauai and Oahu through tonight, while Maui County and the Big Island remain on the drier side. A more typical moderate to locally breezy trade wind pattern will take over Wednesday and Thursday, then restrengthen to breezy by the end of the week.

Discussion

A strong surface high positioned far northwest of the state is being forced south and east due to a progressive trough moving through the mid-latitudes. A shallow cold front, currently identifiable by a band of showery low clouds in the vicinity of Kauai and Oahu, defines the southern edge of the high. Recent radar imagery shows a marked increase in showers moving into windward areas of these islands. Local trades are currently in the breezy to locally strong range this evening, and will continue to increase today in response to pressure rises northeast of the state and an increasing local pressure gradient due to the advancing front.
The aforementioned cold front is quite shallow, with nothing in the way of upper-level support thanks to high pressure aloft parked directly over the state. It will, however, serve as an effective focus for low-level moisture convergence as it interacts with the island terrain. Winds could become quite gusty today behind the leading shower band due to a deep layer of stronger winds behind the front. Have increased winds over and downwind of terrain for Kauai and Oahu today, so portions of those islands have been added to the Wind Advisory already in effect through this afternoon. The latest high-res model guidance has the front stalling in the vicinity of Molokai as it dissipates through Tuesday. This could allow some of the frontal moisture to increase windward showers over portions Maui County late tonight into early Tuesday morning, but leave the Big Island well within the dry airmass.
Heading into Wednesday, a surface trough develops a few hundred miles west of Kauai as an upper level trough closes off northwest of the state. This should serve to weaken the local pressure gradient, allowing a more typical moderate to locally breezy trade wind pattern, characterized by windward and mauka showers favoring the overnight early morning hours, to prevail into the weekend. In the long-term, global models show a strong surface high building in far north- northeast of the state for the latter half of the weekend, which would tighten the pressure gradient over the islands and bring another round of strong, gusty trade winds.

Aviation

Breezy to locally windy trade winds are the result of a strong surface high to the north of the state. A strong trade wind inversion around 08 kft is the result of high pressure aloft. Given both these influences, AIRMET Tango will remain posted for low level turbulence over and downwind of terrain. Both winds and turbulence are expected to improve on Tuesday.
As of 2 am, late night satellite imagery revealed a dense cloud band associated with a dissipating cold front about 35 nm northeast of Kauai and pressing southward. Occasional MVFR conditions in numerous showers are expected with this feature. AIRMET Sierra for mountain obscuration is now in effect for Kauai and Windward Oahu. The front is moving quickly, and drier conditions are expected for the evening hours.
Elsewhere, trade winds will continue to steer shallow bands of stratocumulus towards north and east facing slopes and coasts. These low-topped clouds are expected to produce little rainfall, and VFR conditions will prevail across the eastern two thirds of the state today and tonight.

Marine

Surface high pressure located approximately 1,300 miles north northwest of Oahu is moving east and maintaining a tight pressure gradient over and upstream of the islands. This is producing fresh to strong trade winds across the near and offshore waters. Winds will likely reach gale force through eastern island bays and channels through the day. A Gale Warning is in effect for the typically winder waters around Maui County and Big Island, with a Small Craft Advisory in effect for the remaining waters, through tonight. The arrival of a low to medium period north swell this morning, in tandem with highly-elevated east wind waves generated by these strong trades, will lift combined seas to near or slightly over 10 feet through the day. Seas will approach 12 feet over those waters experiencing gale force winds.
Surf along north-facing shores will see a slight increase through the day as a small, medium period north northwest (340 degree) reinforcement fills in. Areas better exposed to trade swell will also experience an increase in surf heights. North-facing shore surf will then slowly decline from tonight through Thursday. Another small, medium period northwest swell may arrive around Thursday and persist into the weekend to help revive north shore surf heights. Regardless, these series of small impulses will not provide much change to below seasonal average north surf. Small, medium to longer period background south swell, with the occasional medium period south southwest impulse, will hold small surf along south-facing shores through the week. Surf along east-facing shores will remain up the next couple of days in direct response to the fresh to strong winds. Elevated, rough and choppy east surf conditions will peak today before subtly easing into mid week in response to weakening winds.

Fire weather

Northeast trades will continue strengthening today, while a KBDI well over 600 speaks to the dryness of fuels. A dissipating cold front will bring an increase in moisture and showers to the western end of the island chain today. This will improve fire weather conditions over Niihau, Kauai, and Oahu, so the Red Flag Warning has been cancelled for those islands. However, because the front is not expected to reach the eastern half of the state, the dry and stable airmass there will maintain critical fire weather conditions today, and potentially Tuesday, especially during the afternoon relative humidity minimum. The Red Flag Warning remains in effect for leeward areas of Maui County and the Big Island through this evening.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST this evening for Kauai Leeward, Waianae Coast, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Kauai South, East Honolulu, Honolulu Metro, Koolau Leeward, Molokai Leeward South, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Red Flag Warning until 6 PM HST this evening for Molokai Leeward, Lanai Makai, Lanai Mauka, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, South Big Island, Kohala, Big Island Interior.
Gale Warning until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 AM HST Tuesday for all remaining coastal waters.

Data Courtesy of NOAA.gov