textproduct: Honolulu

SYNOPSIS

Surface high pressure continues to strengthen northeast of the state tonight and will bring an increase in trade wind flow. Low clouds and showers will remain through Monday morning mainly over portions of Maui, Molokai, and Oahu as an area of enhanced moisture moves in from the east. From late Monday through Friday, light easterly winds will return. Afternoon coastal sea breezes should help bing clouds and showers to interior and mountainous locations. From Wednesday onward, deeper moisture moving in from the southeast should bring increased precipitation chances to the Big Island, and perhaps Maui.

DISCUSSION

Showers continue this afternoon, mainly over Maui County and Oahu, with only isolated activity on the Big Island and Kauai County. Skies were mostly cloudy except over Kauai County and much of eastern Big Island. Minimal volcanic ash has been observed with today's 39th episode of Kilauea, and most of it has been carried southwest of the crater into relatively uninhabited areas. Winds have become light and variable as of 3 PM HST, allowing the ash to fall out close to the crater, with some light northeast drift.

The overall forecast remains consistent, with minimal changes in guidance. Trades averaging 10 to 20 mph will continue through Monday, then weaken to 5 to 10 mph from Tuesday to the end of the week as the surface pressure gradient slackens again. Rainfall will be light for most areas, but increased moisture will make it to the Big Island from Wednesday into next weekend. This moisture may briefly extend north and west toward Maui County (and perhaps even Oahu) Thursday and Friday, increasing the chance of showers there. This moisture will be associated with an increase in the height of the trade inversion, which makes for slightly deeper and stronger showers. But significant heavy rain is not forecast. The light winds for most of the week means a return to sea breeze showers over leeward areas, along with some weak windward and mauka enhancement.

AVIATION

Moderate and stable trades are expected for the period, along with some occasional land/sea breezes. Low-level moisture embedded within the trades may make for light showers and localized MVFR conditions at times, mainly for Maui County and Oahu, otherwise VFR conditions are expected.

AIRMET Sierra is in effect for mountain obscuration across windward Oahu and Maui County due to the aforementioned light shower activity. This is expected to improve this evening, however.

A sharp, though weak, upper level trough is producing moderate turbulence aloft over the Big Island, where AIRMET Tango is in place above FL300. This is also expected to subside by this evening.

MARINE

A large long-period south-southwest (200 degree) swell will peak tonight into Monday before gradually declining through the rest of the week. Latest 51002 buoy readings remain steady with heights of around 4 to 6 feet at 17 to 19 seconds. The large south-southwest swell combined with King Tides will create the potential for significant wave run up along south and west facing shores this afternoon and Monday afternoon. Due to the potential for significant wave run up, the High Surf Advisory was upgraded to a High Surf Warning for areas exposed to the south-southwest swell.

Very little swell energy is arriving along north facing shores, keeping surf tiny to flat. A small bump in surf is possible for north- facing shores by late Tuesday into Wednesday with the arrival of a small northwest swell and a smaller north swell. Gentle to moderate east-northeasterly winds expected through next week will keep surf along east facing shores below seasonal average.

A Coastal Flood Statement remains in effect for minor coastal flooding of vulnerable low-lying coastal roadways, docks, boat ramps and other coastal infrastructure. King Tides combined with water levels that are running higher than predicted will lead to minor flooding potential around the daily peak tide, which will be during the late afternoon and early evening hours, through at least Tuesday. While minor coastal flooding is expected along all shorelines, the combination of the south-southwest swell, King Tides and the daily high tide will make low-lying coastal areas along south and west shores susceptible to more widespread coastal flooding through the first half of next week.

A Marine Weather Statement also remains in effect due to the large long-period south-southwest swell producing harbor surges and breaking waves near harbor entrances along south and west facing harbors.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Warning until 6 AM HST Tuesday for Big Island South- Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro- Kahoolawe-Kauai South-Kauai Southwest-Kipahulu-Kohala-Kona-Lanai Leeward-Lanai South-Maui Central Valley South-Maui Leeward West- Molokai Leeward South-Molokai Southeast-Niihau-South Haleakala- South Maui/Upcountry-Waianae Coast.