textproduct: Honolulu

SYNOPSIS

The high pressure system north of Hawaii will slowly drift eastward as a low pressure system sets up north of the island chain by Friday. Moderate trade winds will continue a weakening trend producing hybrid trade wind and sea breeze wind flow each day lasting into early next week. Brief passing showers will drift into the islands on the easterly trade winds. Any showers will tend to favor windward mountain areas during the overnight to early morning hours. A more significant change to our weather pattern continues to evolve for early next week from Tuesday through Wednesday. Deeply unstable tropical moisture moving across the state will bring the potential for heavy rain and thunderstorms affecting all islands.

SHORT TERM UPDATE

Satellite and radar imagery show mostly isolated showers moving across the western end of the state on the moderate trade wind flow this morning, with isolated to scattered showers moving into windward and mauka areas of the Big Island and Maui County. The current forecast remains on track with the trade winds expected to ease a little more to become light to moderate today into Friday, allowing for a hybrid trade wind and land/sea breeze pattern to develop. With the mid to upper level low over the state today, the instability associated with this feature will help to support the development of afternoon showers over some leeward and interior areas as sea breezes form. However, limited available moisture and weak lifting mechanisms at the surface will keep the shower activity pretty tame. This mid to upper level low will lift northeastward on Friday and ridging will try to nudge in from the south, limiting shower activity even further. However, deeper moisture will move over the Big Island from the southeast, so increased PoPs slightly for Friday over the Big Island with this morning update. In addition, increased the cloud cover for Friday afternoon as some upper level clouds are expected to move in from the west-southwest.

PREV DISCUSSION

Issued at 321 AM HST Thu Oct 22 2026 The satellite water vapor channel shows a weak upper level low over the state causing unsettled cloud bands to develop across the region, producing brief passing showers as these clouds are lifted up over windward mountain ranges. Drier diurnal weather trends remain in the forecast for the later morning to afternoon hours each day. Expect these conditions to continue through the weekend.

The high pressure system currently north of the state will slowly drift eastward away from the islands as a low pressure system takes its place just north of the Hawaii region. This pressure pattern change will weaken the large scale trade winds through the weekend, and allow a hybrid trade wind afternoon sea breeze wind flow to expand in coverage along the sheltered western mountain slopes of all islands.

A more significant change in our Hawaiian weather pattern is brewing from next week Tuesday onward as a large roughly 1,500 mile long band of deep tropical moisture advects northward over the islands. Expect warm and humid conditions during this time period due to the rising tide of tropical moisture. Global model solutions over the past three days are showing two or three weak cyclonic circulations embedded within this synoptic scale cloud band. Converging winds and upward motions surrounding these embedded lows will provide the forcing mechanism to produce stronger convective heavy rain bands and possibly thunderstorms. Some uncertainty remains in the forecast this far out and the forecast challenge with this pattern lies in predicting the arrival timing of this deeply unstable cloud band and predicting the intensity of these embedded low pressure systems and predicting their locations relative to the Hawaiian Islands. A medium confidence pattern for sure at this point with island by island weather impacts becoming clearer as the forecast time period grows shorter, and our global model solutions improve. Stay tuned.

A Hydrologic Outlook may be needed to cover the rising threats for heavy rain and flash flooding potential during this Tuesday to Wednesday time period. Please continue to closely monitor weather conditions, including the potential for flash flooding early next week as this weather pattern will likely evolve over time.

AVIATION

Scattered windward -SHRA possible today with trades AOB 15kts. VFR cigs/vis prevail through the period with very brief windows of MVFR with the aforementioned -SHRA through the afternoon.

No AIRMETS are in effect.

MARINE

Easterly trade winds will be at gentle to moderate strength through Friday as surface low pressure far north of Hawaii weakens the local pressure gradient. Trades are expected to hold at current strength and shift out of the northeast as high pressure far northwest of Hawaii pushes to low eastward and carries a shallow band of showers over the island chain. The weaker trade winds should persist Monday, but uncertainty increases on Tuesday, hinging on the potential development of a low southwest of the islands.

A small, medium-period northwest swell will provide a small boost to surf along north-facing shores on Friday. A moderate, medium- period north-northwest swell will build late Saturday and peak around seasonal average on Sunday. As this swell declines on Monday, a long-period west-northwest swell will arrive, maintaining moderate surf through the middle of next week.

Small background level surf will prevail along south-facing shores through Friday. A small to moderate, south-southwesterly swell is expected to boost surf to around seasonal average this weekend into early next week.

Along east-facing shores, trade-wind swell will decrease today, though a small, medium-period northeast swell may maintain small surf through Saturday. Aside from wrapping north-northwest swell in exposed areas, east shore surf should remain below seasonal average much of next week.

FIRE WEATHER

Issued at 321 AM HST Thu Oct 22 2026 The high pressure system north of Hawaii will slowly drift eastward as a low pressure system sets up north of the island chain by Friday. Moderate trade winds will continue a weakening trend producing hybrid trade wind and sea breeze wind flow each day lasting into early next week. A more significant change to our weather pattern continues to evolve for early next week from Tuesday through Wednesday. Deeply unstable tropical moisture moving across the state will bring the potential for heavy rain and thunderstorms affecting all islands. The subsidence temperature inversion heights near Maui and the Big Island will remain in the 7500 to 8500 foot elevation range today.

HFO WATCHES/WARNINGS/ADVISORIES

None.