Area Forecast Discussion

SYNOPSIS

An upper-level trough will bring increased high clouds and renewed chances for isolated heavy showers and thunderstorms this afternoon and Monday. Light winds favor chances for mainly afternoon showers Tuesday and Wednesday, followed by rebuilding trade winds Thursday and Friday.

SHORT TERM UPDATE

In general the forecast is on track, so not anticipating any updates this morning. An upper level trough to the west continues to spread high clouds over the state. Thunderstorms are found close to the upper level trough. We continue to monitor for any thunderstorms that could develop closer to the islands this afternoon through tomorrow.

PREV DISCUSSION

Issued at 310 AM HST Sun Apr 19 2026

Today and tomorrow, trades will weaken further and will shift out of the east-southeast across the western half of the island chain, while another upper-level trough brings instability, mainly tonight into Monday morning. For now, it appears that the deepest moisture and highest chances for widespread rainfall will remain along the surface trough northwest of Kauai, but isolated heavy showers or a thunderstorm remain possible around Kauai. Elsewhere, expect afternoon interior showers and possibly a thunderstorm on Big Island, and another item to monitor will be a chance for localized anchored heavy showers along the Koolau Mountains of Oahu tonight. Even though moisture does not appear to be significant on Oahu, the expected veering flow with height has a tendency to produce heavy rain events on the Koolau.

Chances for heavy rainfall look to diminish Tuesday and Wednesday. The upper level trough should move off to the east late Monday, allowing a weak ridge aloft to settle over the state. The GFS and ECMWF are hinting that the surface trough that had been lingering northwest of Kauai will be pushed over the western end of the island chain. This would favor light and variable winds over most areas with higher rainfall chances over island interiors during the late morning and afternoon hours. Trade winds are expected to rebuild Thursday and Friday.

AVIATION

Issued at 310 AM HST Sun Apr 19 2026

Predominately light northeasterly winds among some land-sea breezes will remain in place through the next several days under high pressure well northeast of the Hawaiian Islands and a surface trough lingering to the west. Some terminals may experience some mid- to high-clouds and embedded light showers, resulting in brief periods of MVFR conditions. Otherwise, expect VFR conditions to prevail across most terminals through the period.

No AIRMETs in effect.

MARINE

A trough approaching slowly from the west will allow winds to veer east southeasterly and weaken later today through early next week across the local waters. This feature will also bring a slight chance of thunderstorms to the waters surrounding Kauai this afternoon through mid day Monday. By Thursday, high pressure ridging builds back in north of the state with fresh easterly trade winds returning to the region lasting through next weekend.

Swell, from every direction, and surf will remain very small through late Monday. A small, medium period, northwest swell will move into the region by Monday night and continue through Wednesday. A moderate, medium period northeast swell arrives Tuesday and peaks on Wednesday, bringing moderate surf to north- facing shores, before slowly declining through the end of the week.

A series of overlapping small south swells will move into the region this week keeping surf heights on the small side. Surf heights along east facing shores also remain small due to weaker trade winds until the arrival of the small medium period northeast swell building into the Hawaii region from Tuesday through Thursday.

HFO WATCHES / WARNINGS / ADVISORIES

None.