Drier trade winds will prevail into early next week with light showers on the windward side of the islands. Low level convergence along a surface trough will bring a modest increase in clouds and showers late Monday into Tuesday. More rain is expected through the second half of the week as remnants of Tropical Storm Norbert pass by.
High pressure far to the north is driving gentle trade winds across Hawaii today, weakened by surface troughs to the northeast and east of the area. Visible satellite this afternoon shows partly to mostly cloudy skies across the islands mainly due to the localized sea breezes. Radar shows very little rainfall across the area this afternoon. Light trade winds and isolated showers will continue through the rest of the weekend.
The trough mentioned to the east is forecast to track westward over the next several days. Low level convergence along this feature will bring a modest increase in clouds and showers late Monday into Tuesday, initially reaching the Big Island with showers becoming more diffuse as the trough moves west.
Tropical Storm Norbert is currently around 1675 miles east of Hilo, moving west-northwest at 12 mph. Recent advisory updates from the National Hurricane Center show this system becoming post-tropical on Tuesday while turning slightly west southwest as the motion become dictated by the low level trade winds. Trade winds will strengthen statewide as the gradient tightens around what is left over of Norbert, likely a trough by Thursday and Friday. Rainfall will also increase east to west across the state from Wednesday night through Friday night. A surface and upper trough over the area, with precipitable water values over 2 inches will likely be enough to produce some flooding across the state. Strengthening trade winds will keep showers moving along and focused windward, but leeward sides will also see a fair share of rain. Still a bit far out in the forecast to get too detailed for now, but a definitely a time period to focus on.
A large upper level low well northeast of the islands is weakening the pressure gradient and therefore the trade winds near Hawaii. These weak to moderate trades will continue through Sunday. Winds may become light enough within more wind-protected leeward areas to initiate local topographically-driven breezes. These trades are also relatively dry, and will limit shower activity.
Moderate to locally fresh trades will continue through early next week before gradually strengthening through the latter half of the week. Moisture associated with a weak trough moving in on the trade wind flow may bring a slight uptick in shower activity to the coastal waters Tuesday into Wednesday. While the current forecast has Tropical Storm Norbert dissipating before it nears the Hawaiian coastal waters from the east, remnant moisture from this system is expected to arrive late next week, likely bringing more showers.
Surf along south-facing shores will gradually decline through the weekend as the small, medium- to long-period energy slowly fades. A moderate, long-period swell generated by a low that passed near Australia and New Zealand is forecast to arrive mid to late week next week and bring a bump to south shore surf.
Surf along east-facing shores will remain small to moderate through early next week, then build slightly over the latter half of the week as the trade winds strengthen and some easterly swell from Norbert potentially moves in. Flat to tiny surf along north facing shores is expected through the forecast period.
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