A weak surface trough and its associated moisture plume over the western end of the state will shift northwest through Friday, bringing a slight uptick in shower activity as it passes through. Otherwise, a lighter background flow will allow for a sea/land breeze pattern to persist into the weekend with showers developing over leeward and interior areas each afternoon, followed by clearing at night. Then trade winds will gradually strengthen through next week, shifting the shower focus to windward and mauka areas.
Radar and visible satellite imagery show a slightly veered east- southeast flow steering clouds and isolated showers parallel to the island chain this afternoon. The bulk of the clouds and showers are remaining just east of the state and along a weakly convergent boundary associated with the weak surface trough near Kauai, but clouds and a few showers have also managed to develop over leeward and interior areas of each island with the afternoon sea breezes.
The surface trough will weaken further and gradually shift northwest of the state through Friday, with moderate east- southeast winds filling in behind it through Saturday. Winds will briefly take on an east-northeasterly tilt on Sunday as a front/trough approaches from the northwest. With wind speeds gradually strengthening, a mix of windward and mauka showers with isolated afternoon sea breeze leeward and interior showers can be expected through the weekend. In addition, dew points are expected to remain in the 70s for many locations through Saturday, maintaining muggy conditions through much of the weekend.
Heading into next week, the subtropical high to the far northeast will regain control and easterly trades will build to moderate to breezy levels through midweek. This will usher in slightly lower dew points, and combined with the breezier trades, some relief from the mugginess. Model guidance suggests that an upper level low will pinch off of the longwave trough to the far north and approach the state from the northeast mid to late-week, possibly providing some enhancement to windward and mauka showers as batches of moisture move through.
Gentle to moderate east to east-southeast trade winds continue to push a weak surface trough and associated shallow moisture over the islands. The enhanced low-level moisture has been producing areas of lower than normal MVFR ceilings across windward slopes of Oahu and Maui County, where AIRMET Sierra for mountain obscuration remains in place. Afternoon sea breezes have produced low clouds and isolated showers across interior and leeward terrain, but this activity has been somewhat suppressed by continued stable conditions. Expect improvement over leeward areas this evening and less extensive MVFR ceilings over windward areas on Friday.
Light to moderate trades will hold for the next few days as a weak surface ridge remains to the north and a broad surface trough continues to move west over the island chain the next few days. The weak trough is currently located between Oahu and Kauai waters and is producing some scattered showers over the coastal and offshore waters. Scattered showers will generally decrease over the coastal waters by Friday. Trades may increase slightly over the weekend as the trough dissipates, with more pronounced strengthening early next week as the ridge strengthens to the north.
A moderate, long period south swell is peaking at advisory levels this afternoon, thus a High Surf Advisory remains in effect for all south facing shores through early Friday morning. This swell should drop below advisory levels by Friday as the swell gradually fades late tonight into the weekend. A series of smaller south- southwest swells will fill in Sunday into the first half of next week and will maintain surf near seasonal averages through next week.
Tiny surf will prevail on north and east shores through most of the coming week. A slight increase in east shore surf is expected around next Tuesday or Wednesday as trade winds build across the region.
High Surf Advisory until 6 AM HST Friday for Big Island South- Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro- Kahoolawe-Kauai South-Kauai Southwest-Kona-Lanai Leeward-Lanai South-Maui Central Valley South-Maui Leeward West-Molokai Leeward South-Niihau-South Haleakala-South Maui/Upcountry- Waianae Coast.
