Light to moderate trade winds are expected through the weekend. Brief passing showers will drift into the islands on the northeasterly trade winds, favoring windward and mountain areas during the overnight to early morning hours. A more significant change to our weather pattern continues to evolve for next week. Deep tropical moisture moving across the state will bring the potential for heavy rain and thunderstorms to most islands starting around Tuesday and persisting through at least Thursday.
A surface trough just east of the state is visible on satellite imagery this afternoon, with peripheral clouds and showers tracking into east-facing slopes of the Big Island. This feature will maintain enhanced cloud cover and isolated to scattered showers across windward Big Island and Maui through tonight, before drifting eastward and pulling its deeper moisture away from the state.
Across the broader region, the surface pressure gradient remains relaxed as a broad low to the north splits two highs, one anchored to its east and the other to its west. Consequently, light to moderate trades will persist through Monday, allowing a hybrid trade wind and localized land/sea breeze pattern to take hold. A relatively dry air mass will keep skies mostly sunny to partly cloudy over the smaller islands through this evening, with only isolated windward showers moving in on the northeasterly flow. Meanwhile, high-level cirrus will continue streaming overhead from the west-southwest within a strong subtropical jet streak. Remnants of a dissipating frontal boundary trailing from the northern low as it dips southeastward will brush the western islands Saturday into Saturday night, providing a minor boost to the northeasterly trade wind speeds and windward showers across Kauai and Oahu.
Farther west, a low will attempt to organize near 15N and the Dateline this weekend. The National Hurricane Center currently assigns this feature a low (20 percent) chance of developing into a tropical cyclone over the next 7 days. Regardless of tropical development, the primary concern for Hawaii is an increasing risk of heavy rainfall leading to flash flooding, and isolated thunderstorms next week. This developing low and a large convergent band of deep tropical moisture to its east are expected to get swept up by a passing mid- to upper-level trough and drawn across the island chain. Global models continue to depict precipitable water (PW) values exceeding 2.5 inches over portions of the state late Tuesday through Wednesday, aligning with the strongest upper- level jet support for ascent. However, significant forecast uncertainty remains regarding exact timing, rainfall amounts, and which locations will experience the heaviest totals. Current guidance leans toward heavy rain arriving as early as Tuesday and potentially lingering through Thursday. While large-scale winds are not’t expected to be hazardous, gusty winds may be possible within these heavy showers or in any thunderstorms that may develop.
A strong jet stream just to our north is forecast to shift southward and could produce severe turbulence in and close to SIGMET Romeo. Light to moderate turbulence is possible around Kauai and Oahu between 24 and 32,000 feet.
Light trade winds will continue across most of the terminals where VFR conditions will prevail. PHTO will likely see passing showers later today and overnight which could produce brief MVFR ceilings and visibilities.
No AIRMETs in effect.
A surface low centered about 1000 nm north of islands will move to the southeast through Saturday and will stall roughly 800 to 900 nm northeast of Oahu late Saturday through Monday, keeping the subtropical ridge just north of the area rather weak. Trade winds will be at gentle to moderate strength during much of this time, though a brief period of fresh northeast winds may accompany a shallow band of showers moving over Kauai and Oahu late Saturday. An area of low pressure is expected to move over the islands from the southwest Tuesday and Wednesday, bringing variable winds and the potential for heavy showers and thunderstorms.
Small surf will persist along north shores through early Saturday. A moderate, medium-period north-northwest swell will build late Saturday and produce surf around seasonal average during its peak on Sunday. As this swell declines on Monday, a long-period northwest swell will arrive. This swell will generate moderate surf along north- and west-facing shores through Wednesday. A small north- northeast swell will be possible during the second half of next week.
Small background level surf will prevail along south-facing shores into early Saturday. A series of small overlapping south- southwest swells will push surf back to around seasonal average late Saturday into early next week. A larger south-southwest swell is possible Thursday and next Friday.
Along east-facing shores, wind swell energy will be low through much of the week, but a small medium-period northeast swell will maintain small surf through tonight. Surf along most east facing shores will be small through early next week, but areas exposed to wrapping northerly swells will experience periods of moderate surf late Saturday through Monday and again during the second half of next week.
None.
