Light to moderate east northeasterly flow will prevail today and bring scattered clouds and isolated showers to mainly windward areas. Localized afternoon sea breezes may help initiate a few showers over select leeward mountain slopes. Surface high pressure will build north of the area Monday through midweek and help strengthen trade winds to moderate to breezy levels. A weak surface trough is forecast to move through the area by midweek which could help enhance trade wind showers.
Goes IR satellite imagery loop from this morning shows areas of scattered low clouds drifting towards the windward coasts, as well as the presence of cloud lines southwest of almost every island from leeside confluent boundaries. For the last several hours, isolated showers have been concentrated along the windward slopes with dry conditions elsewhere. Zooming out, a 1025 mb surface high remains parked well to the northeast of state and should help maintain light to moderate east northeasterly trades. By late this morning, sea breezes could form along select leeward locations thanks to this lighter flow pattern. Clouds and showers will be limited today as relatively dry and stable air dominates aloft. On the Big Island, however, hi- resolution model guidance depicts a slight uptick in shower activity this afternoon over the south slopes of Mauna Loa as sea breezes develop and push upslope.
By Monday, a strong surface high begins to expand north of our region and will further establish the moderate trade wind flow. Models advect a batch of low level moisture, caught in this flow, across the western most islands. As the moisture pushes through, expect brief period of increase shower activity. Time- height cross- sections show low level moisture deepening to around 10k feet. By late Monday, this round of moisture pushes west of the state and drier air briefly filters in.
Tuesday through early Thursday, a strong 1030 mb surface high builds well north of the state. In response, local pressure gradients will tighten and trades should increase to moderate to breezy levels. Meanwhile, both the GFS and ECMWF show a surface trough approaching the Big Island from the east, then slowly drifting across the remaining smaller islands. This feature would likely enhance any passing showers as the moisture levels deepen once again and the capping boundary layer temperature inversion weakens. Also during this period, an upper level low drops north of the state and begins to retrograde back to west or southwest. This feature could help enhance shower activity as well, depending how close it passes to the islands. All in all, confidence is increasing for a wetter and breezier period by midweek. For Friday into next weekend, a drier and more seasonable trade wind pattern returns.
Light to moderate easterly trades will persist through Monday, with clouds and showers favoring windward and mauka locations through the early morning hours. Expect some cloud buildups over leeward and interior sections through the afternoon hours where localized sea breezes form. No AIRMETs are anticipated through the period, with only brief periods with MVFR CIGs/VSBYs possible in showers this morning.
A weak high pressure ridge north of the Hawaiian Islands will strengthen by the middle of this week, increasing trade winds and wind driven seas. A low level trough will move through the Hawaii region, from Tuesday through Wednesday, increasing shower activity from east to west.
Several overlapping small medium and long period south swells will continue to pass through the region this week. This south swell energy will keep south shore surf elevated into next weekend.
Surf along west, north and east shores will remain small due to lack of swell energy and lighter trade winds. Increasing trade winds later this week will raise surf heights slightly along all exposed east facing shores.
None.
