Trade winds will remain weak today and allow for sea breeze development along coastal areas by late this morning into the afternoon. Isolated afternoon showers will be mainly limited to interior regions and along mountain slopes. However, these showers should dissipate by this evening with the loss of diurnal heating. Expect a slight uptick in shower activity along windward areas Sunday into Monday, as trades strengthen and an area of marginally enhanced moisture pushes across the state. By midweek, there will be a return to light flow with afternoon sea breeze development and isolated interior showers.
Benign weather conditions prevailed overnight with land breezes helping to keep clouds and showers off the islands and out to sea. The 12Z RAOB soundings from both Lihue and Hilo indicated a rather shallow and stable marine boundary layer with capping temperature inversion height between 5000 to 6000 feet. A weak surface pressure gradient will once again help maintain light background flow today, as surface high pressure resides well northeast of the state and a dissipating frontal system approaches from the northwest. As was the case yesterday, sea breezes will likely form along coastal areas by late this morning into the afternoon. This should aid in the development of scattered clouds and isolated showers over mainly interiors regions and mountain slopes, especially along the lower south slopes of Mauna Loa on the Big Island.
Tonight, surface high pressure begins to strengthen northeast of the islands and will remain anchored in place through Monday. In response, local pressure gradients will tighten and trade winds should strengthen back into the moderate range. Latest short term model guidance depicts an area of enhanced low level moisture moving over the islands from the east northeast late this weekend into early next week, caught up in the trade wind flow. Model time-height cross-sections deepen the boundary layer inversion height to around 8000 feet as the moisture passes through. As reflected in the latest forecast package, expect a slight uptick in clouds and showers along windward locations Sunday into Monday, mainly from Oahu to the Big Island.
Tuesday through Thursday, the aforementioned high moves northward away from the islands, once again allowing for light easterly flow across the state. Both the GFS and ECMWF indicate deeper low level moisture stretching from east to west across the Big Island with drier air positioned further north over the smaller islands. If this scenario comes to fruition, expect the more robust shower activity to be concentrated over the Big Island, while more isolated diurnally driven showers and clouds form over the smaller islands interiors.
Gentle to moderate trades persist through the weekend, leading to localized sea breezes each afternoon. A stable and somewhat dry air mass will maintain mostly VFR condition. Isolated MVFR ceilings will develop over leeward and interior each afternoon and across windward areas overnight.
No AIRMETs are in effect.
Gentle to moderate east-northeasterly winds are expected today as a weak front passing far north of the state displaces the ridge and keeps the trade winds tempered. Moderate to fresh easterly trades will return Sunday through early next week as the surface ridge strengthens, but remains well north of the area.
A Coastal Flood Statement has been issued for isolated minor coastal flooding of vulnerable low-lying coastal roadways, docks, boat ramps and other coastal infrastructure. Peak monthly high 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.
Surf along south and west-facing shores will begin to trend up by this afternoon as forerunners arrive from a large, long-period swell originating from southeast of New Zealand. This swell peaked at the American Samoa buoys around 12 feet 17 seconds Thursday afternoon. Surf will continue to trend up tonight, likely reaching advisory levels on Sunday before peaking Sunday night into Monday near warning levels (but most likely to remain at high-end advisory levels). This swell will also coincide with the peak monthly tides which will add the potential for significant wave runup on top of the aforementioned minor coastal flooding potential during the first half of next week. South shore surf will remain elevated through much of next week due to the slow decline of this large south swell and a series of continued overlapping southerly swells.
Very little swell energy is arriving along north facing shores this morning, keeping surf tiny to flat. A small bump in surf is possible for north-facing shores early next week with the arrival of a small northwest swell and a smaller north swell. Weaker than average trade winds near and upstream of the islands will produce below average surf along east-facing shores through the weekend and into early next week.
None.
