Cloudy skies with generally light winds and periods of showers will persist through midweek. Although widespread heavy rain is not expected during this time, deep tropical moisture will remain in place, particularly over the eastern end of the state. Conditions are expected to deteriorate again by Friday as another upper-level disturbance and surface low approach from the west, bringing increasing chances for widespread rainfall and moderate Kona winds. With soils already saturated from this past weekend, additional rainfall could quickly lead to runoff and flooding impacts.
In the wake of the significant Kona low that impacted the state over the past several days, a broad and persistent upper-level trough remains anchored over the region. While the Kona low has weakened and lifted away, the larger-scale pattern remains largely unchanged, with deep tropical moisture continuing to stream northward over portions of the state. Precipitable water values remain anomalously high, maintaining a moist air mass across the region.
Model guidance continues to indicate a relative decrease in widespread heavy rainfall through the next couple of days, particularly over the western end of the state. However, this should not be interpreted as a return to benign conditions. Periods of showers will persist, with the best chances expected across Maui County and the Big Island, where the axis of deepest moisture is forecast to remain focused through midweek.
By the latter half of the week, the upper-level trough is forecast to deepen west of the state. This feature is expected to re-expand the axis of anomalous moisture back across the entire island chain while increasing large-scale ascent. At the surface, low pressure is forecast to develop and approach the islands, with moderate Kona winds returning and dewpoints climbing back toward 70 degrees.
This evolving pattern will support a renewed increase in shower coverage and intensity from late week into the weekend, with model consensus suggesting an additional several inches of rainfall possible over portions of the state during this period. While this next system does not currently appear to be as intense as the recent event, it will impact an already highly saturated environment.
Given the antecedent conditions, including elevated streams and saturated soils, even moderate rainfall rates may quickly lead to runoff issues. The threat for flash flooding will become elevated statewide by Friday, with the potential for more significant impacts persisting through the weekend.
Passing showers continue over the entire state early this morning as a surface trough moves into the state with intermittent MVFR and IFR conditions at select TAF sites across Maui County and the Big Island. Conditions look to improve over Kauai and Oahu this afternoon as the trough pushes east to Maui County. The trough will keep some showers and MVFR cigs/vsbys around Maui County and the Big Island with isolated periods of IFR conditions through the forecast period.
AIRMET Sierra is in effect for mtn obsc for Kauai, Maui, Lanai, and the Big Island and will likely be extended this morning. Kauai will likely be clear of mtn obsc by this afternoon. No other AIRMETS are currently in effect.
Light and variable winds will prevailing through midweek, with daytime sea breezes and overnight land breezes near the coasts. A brief period of light trades will be possible by midweek as a weak ridge builds north of the state, followed by light to moderate S winds late in the week as a new system approaches from the west.
Surf along exposed north and west facing shores are trending up this morning as a fresh north-northwest swell builds down the island chain. This source should peak today through Wednesday (overhead to double overhead at peak spots), then ease into the second half of the week as it shifts out of the north-northeast.
Surf along S shores will trend up later today through midweek as a fresh long period south swell arrives. This swell will peak Wednesday through Thursday (head high), then ease into the weekend.
Surf along east facing shores will remain well below average due to the lack of trades locally and upstream. The exception will be for east facing shores exposed to north-northeast swells expected later this week/weekend.
None.
