textproduct: Honolulu

SYNOPSIS

An unstable and somewhat wet trade wind pattern will continue through tonight, with brief downpours possible. From Wednesday into early next week, an area of high pressure north of the islands will push drier air into the region. Trades are expected to become windy by Thursday and Friday, then will gradually ease back to locally breezy levels this weekend.

DISCUSSION

Early this morning, local radar imagery shows just a few light scattered showers moving into the islands on locally breezy easterly trade wind flow. Similar to the day prior, the heavier showers that occurred at select spots yesterday quickly diminished during the late afternoon and evening, leaving only light, isolated showers favoring windward areas overnight. Regional satellite imagery early this morning does show a few bands of moisture upstream of the state, however, and although moisture content has decreased from the previous couple of days, the early morning 12z soundings from Lihue and Hilo still show ample precipitable water available.

Drier air is forecast to arrive from tonight into Wednesday night as high pressure north of the state strengthens. In the meantime, expect a relatively wet trade wind weather pattern to continue, with moderate to briefly heavy rain from showers that will generally favor windward and mauka areas, as well as the Kona slopes of the Big Island during the afternoon.

From late Wednesday onward, precipitable water values are anticipated to decrease back down to around 1 inch, and this drier air will persist into next week. Increased stability and stronger trade winds are expected by Thursday. Latest global guidance remains in good agreement with the high to our north strengthening, which should result in windy conditions across the region. Winds could potentially reach Wind Advisory levels Thursday into Friday for some areas, then decreasing back to locally breezy levels during the second half of the weekend.

AVIATION

Moderate to locally breezy trades expected hold for the next couple days. Brief periods of low ceilings and showers will primarily affect windward mountain areas. MVFR conds possible in heavier SHRA, otherwise VFR prevails.

AIRMET Sierra remains in effect for mountain obscuration for windward Kauai, Maui and the entire area of the Big Island. These conditions will diminish later this morning.

MARINE

The pressure gradient back from a surface high centered about 1,400 nautical miles northeast of the islands remains tight enough to support moderate to locally fresh trades the next couple of days. The anchored high will expand and strengthen through mid to late week. The resultant very tight gradient back across the Central Pacific will produce fresh to locally strong to near gale force nearshore winds the later half of the week. A Small Craft Advisory (SCA) is currently in effect over the windier zones surrounding Maui County and Big Island. The SCA will likely be expanded in area later this week to account for more areawide strengthened trades.

A small size, short to medium period north northwest swell is expected to fill in through the day. A gale low skirting the Aleutian Islands the next couple of days will send the tail ends of small north northwest swells through late this week.

A series of small, long period south southwest swells will provide near summer average size surf along south-facing shores throughout the week. Strengthening trades later this week will keep short period, elevated eastern wind wave chop alive well into the weekend.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.