textproduct: Honolulu

SYNOPSIS

Expanding sea breezes favor interior clouds and a couple of showers this afternoon. Trades return early to mid-week favoring showers windward and mauka. A remnant frontal band will bring a brief increase in trade wind showers Friday night.

DISCUSSION

Subtle height falls over the western end of the state favor a trade wind inversion sloping downward from around 10kft at Lihue to 7kft at Hilo. Afternoon sea breezes maintain interior clouds and a few showers this afternoon, but dampened heating beneath abundant high clouds has kept shower coverage and intensity in check. Land breezes will bring clearing this evening, except for portions of Windward Big Island where a few showers are noted moving onshore at press time. Trades then ease back into the area through the first half of the week, building over eastern areas first.

Longwave ridging maintains building high pressure over the north central Pacific through late this week. Attendant surface high then ushers an orphaned frontal band through the islands Friday night bringing strengthening trades and a brief uptick in showers mainly windward and mauka. Noticeably cooler and drier airmass in the wake of this front with dewpoints falling toward 60, perhaps even touching the upper 50s, this weekend.

AVIATION

Light winds have allowed daytime sea breezes to occur today, with afternoon showers over island interiors and kona slopes. Winds will gradually strengthen and become slightly more easterly tomorrow. Showers will decrease tonight but may return over windward and mauka areas, as well as Big Island kona slopes tomorrow. MVFR conditions will occur within showers, while VFR will prevail elsewhere.

AIRMET Sierra is in effect for Kauai due to CLD and SHRA, but these conditions are expected to improve as the evening progresses.

MARINE

A surface ridge near Kauai continues to bring gentle to moderate southeast to south winds to the waters near the smaller islands, and locally fresh east to southeast winds around Big Island. A weakening shearline over the offshore waters northwest of Kauai will continue to weaken and drift to the west over the next day or two. Isolated thunderstorms remain a possibility over the offshore waters near this boundary.

As the shearline drifts west, the ridge will retreat to the north, and this will allow east to southeast winds to spread across the waters from south to north. Easterly trade winds are expected to strengthen Tuesday and Wednesday as high pressure builds to the north. Winds are expected to reach Small Craft Advisory (SCA) levels for the typical windier waters near Maui county and the Big Island. SCA wind conditions may expand to additional waters Thursday as high pressure builds north of the region.

A large, medium period northwest (330-340 degree) swell is expected to arrive late this evening, and build through Monday. This swell is expected to produce surf near High Surf Advisory (HSA) levels along north and west facing shores at its peak. An overlapping long period north-northwest swell will build Monday night and will likely push surf above the advisory level by Tuesday. Resulting seas may reach the 10 foot SCA across exposed waters during the peak of the swell. This swell will gradually decline through the remainder of the week.

A slight increase in choppy east shore surf is expected late Monday though mid-week as trade winds rebuild. Surf along south facing shores will remain tiny to small through the forecast period.

HFO WATCHES/WARNINGS/ADVISORIES

None.