textproduct: Honolulu

SYNOPSIS

Breezy easterly trade winds will persist through tonight, then ease into the light to moderate range from Thursday through Saturday. Clouds and showers will favor windward and mauka areas, with a period of increased shower activity possible through early Thursday as a band of moisture moves through the islands. A few afternoon clouds and showers may develop over interior and leeward areas Thursday through Saturday where localized sea breezes form. Trade winds are expected to strengthen again late this weekend and into early next week.

DISCUSSION

Short-range guidance remains in good agreement and depicts breezy easterly trade winds persisting today as a strong subtropical ridge remains anchored north of the state. A band of moisture over the eastern end of the state, combined with an elevated trade wind inversion near 10 kft and a weak upper-level trough, has led to showery conditions over windward sections of the Big Island and Maui this morning. Overnight upper air sounding at Hilo shows a modest increase in low-level moisture associated with this band, with precipitable water values above climatological normals to 1.57 inches. The latest rainfall summary reflects this showing peak accumulations nearing an inch in some of the windward Maui gauges over the past six hours (ending at 2 AM HST). This moisture may linger through Thursday morning, supporting enhanced rainfall chances across windward areas, potentially expanding to all windward sections of the island chain by tonight.

The surface ridge north of the islands is forecast to weaken from Thursday through Saturday, allowing trade winds to ease into the light to moderate range. At the same time, a drier and more stable air mass is expected to move into the region. As a result, shower activity should become more limited, with passing showers favoring windward and mauka areas during the overnight and early morning hours. Localized sea breezes will develop each afternoon, leading to a few clouds and showers over interior and leeward areas, particularly from Thursday through Saturday.

By late in the weekend and into early next week, strengthening surface ridge north of the state should support a return to a more typical breezy trade wind pattern.

AVIATION

High pressure north of the islands will sustain moderate to locally breezy ENE trade winds today and then decrease a little later tonight. An area of enhanced moisture over the eastern half of the state will continue to bring MVFR showers to Big Island and Maui windward areas today and could spread to the other islands later today and tonight at a lesser extent. MVFR conditions are expected within showers, while VFR prevails elsewhere.

AIRMET Sierra is in effect for windward Maui and the Big Island due to frequent shower activity causing mountain obscuration. This should continue through much of the morning and may spread to other islands.

MARINE

Surface ridge north of the area will hold today, then weaken Thursday through Saturday as a front passes far north of the state. Moderate to locally fresh trades will persist today before easing into the light to moderate category Thursday through Saturday. Fresh to locally strong easterly trades will return Sunday through early next week.

A series of southern hemisphere swells will continue through the week with the larger south swell of the week due to arrive this weekend. Currently, a small, medium-period south swell is overlapping a fading swell, producing near seasonal average surf along south facing shores. These swells will slowly decline through Thursday. A smaller pulse of south-southwest swells will fill in late Thursday into Friday keeping surf elevated along south facing shores.

Long-period energy from a storm that passed within our swell window around New Zealand earlier this week is expected to gradually fill in locally through the weekend. Wave models have this swell peaking Sunday into Monday that could drive surf heights to near the warning level. This swell will coincide with the peak monthly tides and will likely lead to significant wave runup and minor coastal flooding during the first half of next week, particularly during the peak daily high tide cycles.

A small west-northwest swell will hold into Wednesday and fade Thursday. East shore surf will slowly decline below seasonal averages through the rest of the week as trades ease.

HFO WATCHES/WARNINGS/ADVISORIES

None.