A high pressure system will strengthen north of the Hawaiian Islands, producing moderate to locally windy trades. Light to moderate showers will focus over windward and mauka areas with brief showers spilling over to leeward areas, especially during the overnight and early morning hours. Confidence is increasing that an upper level trough will deepen to the north of the state from Thursday into next weekend, creating a surface low to our north. This would turn our winds out of the southeast starting around Thursday, and may eventually drive a weak front through the state.
Two radars (Molokai and Upolu) remain temporarily out of service, limiting radar coverage from Oahu to northern portions of the Big Island. With that said, the two functioning radars showed isolated windward and mauka showers over Kauai and eastern Big Island. Satellite indicated a typical trade wind pattern of mostly cloudy windward and mostly sunny leeward across most islands. Winds were gusty and mainly out of the northeast. Average speeds were 15 to 20 mph, with gusts of 30 to 40 mph.
A large surface high pressure system was centered near 35N and 155W this afternoon. This high will remain nearly stationary for the next few days, then weaken and begin to move east Wednesday. As it does, a low will move in from the northwest. While the exact track this low ends up taking is not known with confidence at this time (the time frame involved is Thursday into next weekend), it appears there is enough agreement within the model suite to forecast a change to southeast winds sometime around Thursday. After that, if the low drops far enough south, it may push a cold front through the state just after the forecast period ends (so next Sunday or Monday).
In the meantime, we'll see a typical trade wind pattern of mainly windward and mauka showers, with a few making it over to leeward areas due to the relatively strong winds. These showers will be most numerous at night and in the early morning, as usual. Winds will gradually weaken from Tuesday into Wednesday.
Breezy trades. Isolated to scattered showers, concentrated mainly along windward and mauka locations, most numerous late at night through the mornings. Showers may produce brief periods of MVFR ceilings and visibility.
AIRMET Sierra remains in effect for north through east sections of the Big Island above 2500 feet due to low clouds and showers.
AIRMET Tango remains in effect for for tempo moderate turbulence downwind of terrain below 9000 ft.
Robust surface high pressure centered far north of Hawaii will maintain fresh to strong trade winds at current strength for the next couple of days, and a Small Craft Advisory (SCA) remains in effect for all waters except windward Big Island through early Tuesday. Trades will steadily decrease late Tuesday and Wednesday as the high weakens and is displaced eastward by an approaching low far northwest of the islands. The SCA will likely be trimmed back to the typically windy waters around Big Island and Maui at that time. Trade winds will lower to gentle strength, or may become disrupted, as the low passes to the north Thursday and Friday.
A north-northwest swell and a smaller overlapping west-northwest swell will slowly decline through Monday and fade on Tuesday. A very small northwest swell may arrive Thursday, followed by a moderate north- northwest swell next weekend.
The current south swell will continue a slow decline over the next day or so. South shore surf will drop below seasonal average Monday and will remain relatively small through much of the week. A moderate south-southwest swell is expected next weekend.
Rough trade wind swell will produce east shore surf just above seasonal average through Tuesday, then decline later in the week as trade winds decrease.
Small Craft Advisory until 6 AM HST Tuesday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Kaiwi Channel-Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters-Maalaea Bay-Maui County Leeward Waters-Maui County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters-Pailolo Channel.
