375 FXHW60 PHFO 071940 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 940 AM HST Tue May 7 2019 .SYNOPSIS... Light and variable winds will continue through Wednesday, with light trade winds expected to return Thursday and Friday. Trade winds will then gradually strengthen over the weekend, becoming locally breezy early next week. With the light winds, afternoon sea breezes will drive cloud formation over interior and mauka areas, with little in the way of rainfall. The returning trade winds will tend to focus clouds and showers over windward areas, but the island atmosphere will remain stable, and only brief passing showers are expected. && .DISCUSSION... The islands lie in an area of light and variable winds, as a complex area of low pressure lies between the islands and the trade wind supporting high to the NE. Morning soundings show a dry and stable air mass in place, with a strong subsidence inversion based between 5000' and 6000', and PWAT near 1.1". Satellite shows nearly clear skies over windward waters, and partly to mostly cloudy skies over leeward waters, where radar is picking up a few light showers. Over the islands, mostly sunny skies prevailed early this morning, except for an area of stable low clouds that was lurking over Oahu. However, latest images show stable low clouds increasing over the lower slopes of all islands over the last hour or so. The complex low NE of the islands will gradually dissipate over the next 48 hours or so, as a relatively weak high pressure cell passes well N of the islands. Latest guidance indicates that a weak trough will linger NE and N of the islands through Friday, so although we are expecting the high to support light trade winds on Thursday/Friday, wind speeds will likely be sufficiently light to allow land and sea breezes to dominate winds over land. As the trough dissipates and another high builds to the NW and N of the islands over the weekend, moderate trade winds are expected. The high will sit far NE of the islands next week, and seasonable moderate to locally breezy trade winds are expected. The light winds will allow afternoon sea breezes to drive cloud and shower formation over island interiors, but little significant rainfall is expected as the island atmosphere will be stable due to the presence of a mid-level ridge that will be building over the islands this weekend. So, even as trades return, passing windward showers are expected to be brief, with little significant accumulation. && .AVIATION... Light flow over the region today will allow for weak diurnal sea breeze/land breeze development. Expect variable low cloud cover with bases generally above 2500 feet MSL. Other than ISOL -SHRA that may develop over the interior later this afternoon, conditions will remain VFR. No AIRMETS are anticipated today. && .MARINE... Light and variable winds due to a weak trough of low pressure over the region will continue through Wednesday and weaken north of the state Thursday and Friday. A ridge of high pressure will build northwest of the state Thursday and will bring light to moderate trades Thursday through the weekend. Despite the return of light to moderate background east to northeast trade flow through the second half of the week, overnight and early morning land breezes followed by late morning/afternoon sea breezes will remain likely near most coasts each day. Surf along north facing shores will lower today as the current small nine second swell eases. A fresh northwest swell associated a gale that has tracked east of the Date Line near the Aleutians over the past couple of days will build down the island chain late Wednesday, then peak Wednesday night through Thursday before easing into the weekend. A small northwest swell associated with a compact gale that is forecast to develop Wednesday night into Thursday as it tracks east-northeastward across the Date Line will be a possibility late Sunday through Monday. Surf along north and west facing shores associated with this feature, if it evolves, will be minimal. Surf along south facing shores will remain small through midweek with mainly a combo of south-southeast and south-southwest swell energy continuing. An upward trend is expected late Thursday through the weekend due to an active pattern down south featuring two powerful lows passing far south of New Zealand within Hawaii's swell window. Back-to-back long-period south swells moving through locally will result with the first one filling in by Thursday night and the second one filling in Saturday out of the same direction (190 deg). The first swell has already begun to move through the Pago Pago buoy, which increases the confidence for an arrival locally by Thursday night. The second one will be the larger of the two, which may result in the first high surf advisory of the season for south facing shores Saturday night into Monday. The factors that reduce forecast confidence in heights reaching advisory levels is that the northern extent of this fetch was farther south and aimed more so at the Americas. Confidence will increase by Thursday as this energy moves through the Pago Pago buoy. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Birchard AVIATION...JT MARINE...Kino