FORECAST DISCUSSION

Synopsis

A weak front will reach Kauai late this afternoon and move into Oahu on Memorial Day. The front will then stall and slowly dissipate as it moves across the eastern islands through mid week. High pressure will build north of the state behind the front, allowing the trade winds to return for much of next week.

Update

Initial visible satellite images of the day reveal nearly clear skies across the state this morning, except for lingering low cloudiness over the Kau and Kona districts on the Big Island. Land breezes are also keeping clouds and isolated showers from moving ashore. The forecast has been updated to reflect current conditions, and also to slightly increase afternoon POPs over interior Oahu and leeward Big Island.

Prev discussion issued 355 am hst

Currently at the surface, weak and broad troughing is present over the islands this morning, with a better defined cold front located around 150 miles north of Kauai. Infrared satellite imagery shows clear to partly cloudy skies in place across most of the state, with more extensive cloud cover over the Big Island where the majority of shower activity has been seen overnight. Main short term concern for today revolves around rain chances. Today... Weak troughing will remain in place across the islands through the day, while the cold front makes steady progress southeastward, reaching Kauai by late this afternoon. Winds are expected to remain light, allowing for sea breeze development in most areas. This in combination with precipitable water (PW) values between 1.3 and 1.5 inches and weak low level inversions, should be enough for scattered to numerous showers to develop across the interior of the islands once again this afternoon. Tonight through Wednesday night... The front will push through Kauai Tonight and into Oahu on Memorial Day, then slowly weaken over the central and eastern islands through Wednesday night. High pressure will build in behind the front, so expect the trade winds to gradually return from northwest to southeast down the island chain. PW values remain above climatology, generally in the 1.3 to 1.7 inch range in association with the front, so conditions are likely to remain wetter than normal through the period. Additionally, the majority of the shower activity should transition to windward and mauka locales as a result of the returning trades. Thursday through Saturday... High pressure will weaken to the north of the state, and this will lighten the trade wind flow. PW values will also drop close to seasonal levels, so we should see a fairly typical trade wind weather pattern with clouds and showers focused primarily across windward and mauka areas.

Aviation

Light winds continue to prevail across the area early this morning, with land breezes. Expect mainly VFR conditions to prevail, though lingering clouds along Kona areas of the Big Island may bring isol MVFR ceiling. Similar weather conditions are expected over the state today. Hence, widespread sea breezes will once again return to the islands later today, with clouds and showers developing from late morning into the early evening hours, producing localized MVFR ceiling and SHRA, with possibly isolated IFR conditions. There is no AIRMET in effect at this time, though AIRMET mtn obsc is possible again by the afternoon, depending on how extensive the afternoon cloudiness will be.

Marine

The latest observations at the nearshore Lanai and Barbers PACIOOS buoys remain in line with the latest nearshore wave model guidance and are holding steady in the 2 to 3 ft range at 14 to 15 seconds out of the south-southwest (210 deg). This southerly source will continue to fade into Monday, before being reinforced by a similar southerly source Tuesday through the mid-week period. A small northwest (320 degrees) swell is forecast to fill in through the day today, peak on Monday, then gradually ease Tuesday and Wednesday. Winds will remain light across the area today as a weak front slowly pushes east across the region. Similar to the past couple of days, this will translate to light offshore winds at the area beaches through the morning hours, before shifting to onshore through the late morning and afternoon period today. Moderate to fresh trade winds will return through the week as high pressure builds north of the state in the wake of the frontal boundary. Although the winds are forecast to remain below advisory levels, the typical windier marine areas between Maui County and the Big Island may approach or near these levels periodically through the week and will need to be monitored.

HFO Watches/Warnings/Advisories

None.

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