textproduct: Honolulu

SYNOPSIS

Scattered showers across Maui County and the Big Island should decrease this evening as weather conditions stabilize. A fair weather day is expected across many areas on Sunday with sea breezes developing during the day. A dissipating front is expected to brush the state Sunday night into Monday, which should bring an increase of showers primarily over windward and mauka areas through Monday.

DISCUSSION

Water vapor satellite imagery show a short-wave trough swinging through the state with showers and isolated thunderstorms developing ahead of the trough axis, which is centered near Molokai. For rest of this afternoon, scattered showers and isolated thunderstorms will be possible over Maui and the Big Island with brief periods of heavy rainfall possible. Showers will generally be on the decrease this evening with conditions stabilizing overnight and land breezes developing across many areas.

Another interesting feature seen on satellite is the volcanic plume caused by the Kilauea eruption today. Satellite estimated the plume heights to be over 35,000 feet and we have received pilot reports of the plume reaching 38,000 feet earlier today. The volcanic plume has weakened some from earlier today but you can still see the plume drifting towards the east due to the westerly winds aloft. Due to the significant amounts of debris/tephra/ashfall falling in public areas surrounding Kilauea, a Ashfall Warning was issued earlier today.

For Sunday, an upper level ridge building over the state will bring stable conditions. At the surface, a ridge of high pressure near the state will result in light and variable winds. Daytime sea breezes will develop in many areas, which should allow for afternoon clouds and some scattered showers over interior and mountain areas. Any shower activity should remain light to moderate in intensity due to the stable atmosphere.

Starting Sunday night, weather conditions will begin to change as the tail end of a cold front approaches the state from the north. There are still quite a bit of uncertainty regarding the how far south the cold front will get with the GFS model showing the front stalling out and dissipating just north of the state. At the surface, with a 1021 mb high building to the north of the state behind the front, I am leaning towards the ECMWF solution with scattered showers increasing across the smaller islands Sunday night into Monday. Moderate to locally breezy trades should increase on Monday if the ECMWF solution holds true.

In the extended, an upper level ridge will build over the state on Tuesday with a surface ridge expected near the state as well. Stable conditions are expected with light and variable winds expected from Tuesday through at least Thursday. A land and sea breeze pattern is expected during this time with afternoon clouds and light showers possible over interior and mountain areas.

AVIATION

Ashfall from Kilauea has impacted aviation near and south through southeast of Hilo, and an ashfall warning is in effect.

Scattered showers continue this afternoon, but most locations remain in VFR conditions. Isolated thunderstorms have formed on Big Island. Surface winds are fairly light and in most areas have come around out of the southeast, but many leeward areas are seeing west or northwest winds due to seabreeze impacts. Drier conditions are expected tomorrow with predominantly VFR conditions statewide.

Currently, no AIRMETs are effect.

MARINE

Light to moderate trades veer to southerly and become variable at times as a front approaches from the west. Light trades briefly return early next week followed by another around of variable to southerly winds ahead of another front.

For N shores, short period remnants of existing NW swell are on the decline today and surf will follow suit as the period continues to shorten and swell size declines. A new small, medium to long period NW swell builds across area waters tonight and quickly peaks during the overnight hours resulting in a brief overnight bump to surf. Energy directed at N facing shores then fades into early next week. A moderate medium to long period swell maintains elevated surf during the middle of next week followed by a large medium period NW swell during the late week period. This latter swell is forecast to peak near the High Surf Warning threshold for N and W facing shores.

Surf along E shores remains small into next week owing to a lack of trades. S shores remain nearly flat in the near term with a small boost from tiny long period energy poised to arrive late Sunday and continuing well into next week.

HFO WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 6 AM HST Sunday for Big Island Summits.