FORECAST DISCUSSION

Synopsis

Areas of high pressure will reside north of the area through the week. The result will be for a breezy trade wind weather pattern across the state. Clouds and passing light showers will favor windward and mauka areas while most leeward locations will generally be dry. Winds are expected to diminish a bit over the weekend as an area of low pressure develops northwest of the area.

Discussion

Breezy to locally windy trade wind weather can be expected over the next several days as areas of high pressure reside north of the state. One area of high pressure will be passing by from west to east tonight and Tuesday. A front will pass by well north of the area which may result in a brief downtick in winds speeds on Tuesday. However another high will quickly build in north northwest of the area by Wednesday with a slight uptick in winds expected. The airmass over the area is rather dry and stable. However moisture embedded in the trades is providing for clouds and some passing light showers to fall over windward and mauka areas. This weather pattern is expected to continue for the next several days with shower activity highly dependent on incoming moisture availability. Cold temperatures aloft combined with some elevated moisture may allow for a slight chance of thunderstorms as well as the potential for a bit of freezing rain over The Big Island summits both Tuesday and Wednesday afternoon.Winds will begin to drop off later in the week as the pressure gradient over the area relaxes just a bit. As we head into early next week, global models indicate a mid level trough of low pressure will develop to the north and northwest of the area. This may cause for a less stable airmass to be in place with an uptick in shower activity possible. There are differences in the low level pattern with the GFS indicating us remaining in a light to moderate trade wind environment with moisture riding in on the trades, while the ECMWF has a lighter wind field over the area with some moisture being drawn up from the south over the area. Thus confidence on any real specifics in the weather details is rather low in the long range forecast.

Aviation

A strong high pressure system located north of the Hawaiian Islands will continue to produce strong northeast trade winds for the next few days. A strong low level inversion will keep cloud tops on ceilings below 7 kft for most areas with higher cloud tops up to 12 kft on the Big Island. Mostly VFR conditions are expected with scattered light showers and isolated MVFR along windward slopes. A few thunderstorms are possible over mountain interior areas of the Big Island on Tuesday afternoon. AIRMET Tango in effect for moderate turbulence over and south through west of all islands. Conditions likely continue through Tuesday.

Marine

Strong high pressure passing about 500 nm north of Kauai will keep strong to gale force trade winds in place tonight. A recent ASCAT pass detected some gale force winds in the Alenuihaha Channel and large areas of 25 to 30 kt winds elsewhere across waters around the eastern half of the island chain. With the surface high passing due north of the state tonight, we expect little change in winds and have elected to extend the gale warning for the Alenuihaha and Pailolo Channels and Maalaea Bay today. A Small Craft Advisory (SCA) remains in place for the remaining waters tonight, and with the gale warning likely expiring by morning, expect an SCA to be in place for all waters on Tuesday. Another area of high pressure will build north of the islands late Tuesday and Wednesday, likely keeping SCA conditions in place over most waters through Wednesday or Thursday. A steady decline in winds is expected heading into the weekend. Large combined seas comprised of a mix of north-northwest swell and wind waves are producing high surf across north facing shores and hazardous seas contributing to the SCA. Combined seas at the NOAA buoys to the northwest of the islands are down to 8 to 9 ft at 11 to 12 seconds, while larger seas mainly passing just east of the islands are down to 13 ft at 14 seconds at buoy 51000. These declining seas are still 2 to 3 ft above Wavewatch guidance at the local PacIOOS buoys and are high enough to warrant the extension of the High Surf Advisory (HSA) for north facing shores through the night. Based on the NOAA buoy data, expect surf to be below the advisory level before daybreak with a steady decline expected through the day on Tuesday. A pair of long period swells from distant sources will produce somewhat elevated surf along north and west facing shores later this week, while rough, short period trade wind seas maintain surf near to just below advisory levels along east facing shores through Thursday. The first northwest swell is expected to arrive on Wednesday and peak in the double overhead range Wednesday night and Thursday. The second northwest swell will likely be larger and may lead to advisory level surf Friday night and Saturday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for Niihau, Kauai Windward, Kauai Leeward, Oahu North Shore, Oahu Koolau, Molokai, Maui Windward West, Maui Central Valley, Windward Haleakala, Big Island North and East. Wind Advisory until 6 AM HST Tuesday for Lanai, Kahoolawe, South Big Island, Big Island North and East, Kohala. Small Craft Advisory until 6 PM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters. Gale Warning until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

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Synopsis/Discussion...Burke Aviation...Bohlin Marine...Wroe

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