textproduct: Honolulu

SYNOPSIS

Surface high pressure centered northeast of the state will continue to drive moderate to locally breezy trades across the islands today. There will be a decrease in cloud and shower coverage as the day progresses as a drier and more stable airmass moves in. Expect little change in the weather pattern on Tuesday, though trades will be slightly weaker. Wednesday into Thursday, light easterly flow will lead to a sea breeze and land breeze regimen. Thus, most cloud cover and shower activity will be limited to interior and mountainous terrain during the afternoons. In addition, deeper moisture moving in from the southeast Wednesday through Friday should bring increased precipitation chances to the Big Island, and perhaps Maui.

DISCUSSION

IR satellite loop and RADAR imagery from early this morning continued to show a band of low clouds and scattered showers pushing westward over the island chain. Rainfall amounts from midnight have not been all that impressive, with windward sites on all islands picking up less than a quarter inch of rainfall accumulation. On Oahu, the cloud layer was deep enough to spill over the Koolau range and onto leeward locations, though only a few hundredths of an inch were reported.

A 1025 mb surface high, centered roughly 1,600 miles northeast of the state, will remain parked in place through late today and allow moderate to locally breezy trades to linger. Cloud cover and showers should gradually dwindle through the day as these trades help usher in a drier airmass. As stability aloft increases, a model time-height cross-section shows the boundary layer temperature inversion height, or capping inversion, lowering to 5000 to 6000 feet. A few isolated showers may affect windward locations late today through tonight night, but nothing of significance. Tuesday's weather to be very similar to today's, though the aforementioned surface high lifts further north, away from Hawaii, leading to slightly weaker trades.

On Wednesday, an upper level trough begins to dig southward over the central north Pacific, along with the development of a surface frontal boundary northwest of the state. This should help weaken local pressure gradients further and bring light and variable background flow. For the smaller islands, diurnal heating, combined with weak surface flow, will lead to a diurnal sea breezes and nocturnal land breezes. Clouds and showers should mainly be limited to over the island interiors and mountainous terrain. Meanwhile, by late Wednesday, both the GFS and ECMWF have been consistent with advecting a pocket of deeper moisture associated with a weak surface trough up from the southeast towards the Big Island. This feature could act to increase shower coverage, especially along eastern portions of the Big Island. The exact timing and and impacts, if any, from this potential increase in rainfall will be refined in the coming days. Long range models continue to push this band of moisture up through Maui County and to a lesser extent Oahu on Thursday into Friday, before lifting it northward. Light southeast flow, combined with this batch of moisture, could lead to an increase in shower activity over the islands interiors during the afternoons. Typical June trade wind weather should by this weekend.

AVIATION

Light to moderate trades persist through the morning hours, occasionally light enough for sea breezes to develop. Trades increase slightly throughout the morning, with periods of gusty winds at times. Low-level moisture embedded within these trades may lead to light shower activity resulting in periodic MVFR conditions, namely across windward and mauka areas. Otherwise, VFR conditions prevail.

AIRMET Tango remains in effect for moderate turbulence over the Big Island between FL300 to FL400.

MARINE

Moderate trade winds today will become light to moderate with local land and sea breezes through the week as high pressure weakens.

The large long period south southwest swell will hold around warning levels today and a High Surf Warning is in place through tonight. Buoy 51002 readings this morning are hovering around 4 to 6 feet at 17 to 19 seconds. As the period has dropped slightly from yesterday, the consistency of the sets could increase, which could lead to more water accumulating near the shorelines. The surf will then gradually lower Tuesday and Wednesday, then another pulse arrives Wednesday night into Thursday which could push surf back up to advisory levels. The large south- southwest swell combined with King Tides will continue to create the potential for significant wave run up along south and west facing shores through the afternoon.

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 Niihau-Kauai Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kohala- Kauai South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Southeast-Molokai Leeward South-Lanai Leeward-Lanai South-Maui Central Valley South-Kipahulu-South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast.