textproduct: Honolulu

SYNOPSIS

We'll see another day of light winds with a few showers, mainly driven by sea-breezes. A cold front is expected to move through the state Sunday night into Monday, bringing a line of showers. Relatively dry northerly winds will follow this front, providing for a cool Tuesday morning. A second front is forecast to move through Wednesday night into Thursday. Neither of these systems appear to be flooding threats at this time.

DISCUSSION

Showers continue this morning on the Big Island from Cape Kumukahi southwest to South Cape, but the strongest showers are now offshore as downsloping winds have pushed most of the activity off the coast. Elsewhere, skies were mostly clear over the other islands.

The latest guidance is very similar to previous runs, showing a boundary stalling just west and north of the state today. This will bring enhanced moisture mainly to the western end of the state, but ridging aloft will bring too much stability, so showers are not expected to be numerous or strong. Additional showers are forecast for much of the Big Island, where weak southeast winds will allow for a healthy dose of sea-breeze convergence-driven convection. Saturday, the boundary will wash out and what little is left will pull back to the north and west, leaving another day of spotty sea-breeze driven showers.

Sunday, an upper level trough will move across the Central Pacific not too far north of the state, pushing a front toward the area. This front will pick up the leftover moisture from the previous system and push across the state from west to east. It is forecast to reach Kauai County Sunday night, Oahu and Maui Monday morning, and the Big Island Monday afternoon. The front should be accompanied by a band of moderate to strong showers followed quickly by relatively cool and dry northerly surface winds. Showers should be moving fast enough to limit any flooding threat. In the airmass behind the front, lows Tuesday morning should be around 5 degrees below normal, and likely even lower in sheltered valley locations of the western islands where cloud cover should be minimal. Trades will resume behind the front as surface high pressure builds back into the region.

Wednesday, the old frontal band will move back westward over the state as a new front approaches from the northwest. This next front will be helped along by yet another upper level trough just to the north, and should move across the area Wednesday night into Thursday. At this time, the moisture associated with this trough appears to be less impressive than the previous one. However, much can change in the model solutions between now and next Thursday, so it bears close watching. Finally, models show a surface high building in behind this front, bringing another round of trade winds and more typical weather for Friday.

AVIATION

A weakening frontal boundary will stall out near Kauai later today. Expect increasing shower trends for airfields on the Garden Isle later this morning with brief periods of MVFR conditions in showers lasting into Saturday.

AIRMET Sierra remains in effect for mountain obscuration above 2000 feet, this AIRMET will diminish later this morning. AIRMET Sierra may need to return for Kauai later this afternoon.

MARINE

A high pressure ridge over the central waters will remain stationary as a front approaches from the northwest. Light to gentle southeast to southerly winds will rule over the marine waters today. As the front dissipates and its remnants lift northward, gentle east to southeast winds will prevail Saturday and early Sunday, giving way to southerly winds again late Sunday. Due to these lighter winds, land and sea breezes are possible through the weekend. A stronger front will move down the island chain Monday and Tuesday, likely ushering in fresh northerly winds in it wake.

Surf along north facing shores will remain small as the west- northwest swell continues to gradually decline. Surf is expected to build in rapidly Saturday with long period forerunners potentially reaching the offshore buys this afternoon. This large long period northwest northwest (330 degrees) swell that likely peak Saturday evening producing surf near High Surf Warning (HSW) levels along north and some west facing shores. Surf will remain elevated on Sunday before a potentially even larger long period northwest (320-330 deg) swell will build through the day on Monday and hold through Tuesday likely above the HSW thresholds. Stay tuned as the low develops. Surf will likely remain elevated through the middle of next week.

Surf along east facing shores will continue to decline through the weekend as winds over and upwind of Hawaii remain weak. Some increase in east shore surf is possible early next week. Along south shores, surf will remain very small through the forecast period.

HFO WATCHES/WARNINGS/ADVISORIES

None.