Rain chances will steadily increase through the week as moderate southerly winds associated with an approaching cold front and upper-level disturbance draw moisture northward into the islands. The front may reach the state later in the week, potentially leading to more widespread rainfall by the weekend.
Forecast guidance remains in good agreement through the first half of the week, depicting a deep low pressure system west of the islands gradually shifting east. This will cause low-level winds to veer out of the south and strengthen to moderate speeds beginning today. As this pattern evolves, mid- to upper-level heights will lower, and increased moisture will begin streaming northward into the region, initially affecting the western end of the state. As a result, expect mostly cloudy skies at times, with a steady uptick in rain chances. Expect humid conditions, and vog is likely to linger due to the continued south to southeast flow.
Confidence is increasing for the latter half of the week as models and ensemble solutions show better alignment. A deep moisture axis and frontal boundary are expected to reach the western islands Wednesday night into Thursday before gradually stalling and weakening. This moisture, combined with broad upper- level troughing and instability, will support a wetter pattern that may become more widespread heading into the weekend. While much of the rainfall will return to typical windward areas as breezy trades fill in, some showers will likely carry over to leeward areas of the smaller islands due to lingering instability and an elevated and weak inversion.
Light southeast to south flow will allow for land breezes through mid morning. Isolated light showers may drift over the islands, but not expecting anything widespread. By late morning, southerly winds will begin to strengthen to moderate levels, in response to a frontal system approaching the island chain from the northwest. Scattered showers may develop over mainly interior regions this afternoon with isolated activity elsewhere. There may brief periods of MVFR ceilings with any of the more robust showers.
All locations can expect to see some VOG with the degassing of Kilauea. It is not impacting vsbys enough to be put into any of the TAFs but is worth mentioning for general awareness.
No AIRMETs are in effect
A storm system to the distant northwest, will strengthen winds and shift them around to the southeast and south today through Tuesday. Localized terrain enhancement around the Big Island and Kauai will likely result in advisory level winds, and a Small Craft Advisory (SCA) remains in effect for these areas beginning Noon today and continuing through 6 PM Tuesday. The SCA may eventually need to be extended through Tuesday night. The winds will gradually ease Wednesday and Thursday as a front approaches from the northwest, with moderate to fresh northeast trades filling in behind the front for the end of the week.
A series of small overlapping north-northeast swells will keep some surf in place along exposed north and east facing shores through midweek. A small west-northwest swell will bring some small surf to exposed north and west facing Tuesday through Thursday. A more significant north-northwest swell appears to arrive late in the week, potentially bringing warning level surf to north and west facing shores over the weekend.
Surf along south facing shores will gradually lower today, then hold near seasonal levels tonight through late in the week. Surf could become a bit choppy later today through Wednesday.
Small Craft Advisory from noon today to 6 PM HST Tuesday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Big Island Windward Waters-Big Island Leeward Waters.
