textproduct: Honolulu

SYNOPSIS

A band of showers, some heavy, will develop over the western half of the state tonight and bring rainfall early next week. Winds remain light through much of the forecast period with moderate trades building in by the end of the week.

SHORT TERM UPDATE

Issued at 902 AM HST Sat Apr 11 2026

Dry air filling in behind the departing low brings high stability to the Lihue sounding this morning while Hilo remains saturated to the tropopause. However, developing subsidence and weak dry advection will scour this moisture out today. Radar returns have rapidly dimished over the Big Island and the forecast has been updated accordingly.

Scattered light showers continue lifting SW-NE in the Kaiwi Channel and western Maui County. These showers are developing along a weakly convergent remnant surface boundary where SW mid- level winds have already begun advecting deeper moisture back into the central portion of the state. These showers will remain light in the very near term, but the boundary could serve as a focus for afternoon convection as it wavers between Oahu and Molokai. However, ample high clouds limit confidence for heavy afternoon showers as depicted in the latest hi-res.

Although radar presentation this morning remains modest, model cross-sections are actually impressive with how quickly a deep, convergent frontal structure redevelops over central Hawaii. As right entrance jet forcing increases tonight, the front rapidly builds to jet level and is modeled to have an appreciable frontal circulation in the presence of otherwise very weak forcing. This sets the stage for a rather narrow band of fairly stationary shower activity to develop over or in the vicinity of Oahu tonight. The hi-res guidance is very aggressive in depicting heavy rainfall potential, though these models tend to run hot in moisture-rich environments. Even so, the global models also key in on a narrow band of moderate to heavy rain that may not move much for 24 hours or so. Several inches of rain will be possible beneath this band, which is most likely to set up somewhere between the Kauai Channel and Molokai, though Kauai and western Maui are not out of the game. At this time, Oahu appears to be the highest probability landing spot, but details governing the ultimate position of the frontal band are likely to be lost in the noise and uncertainty probably remains high until it becomes evident on radar. Uncertainty is high enough to warrant keeping Big Island in the statewide Flood Watch, but the probability of meaningful rainfall is lowest there.

PREV DISCUSSION

A residual axis of deep tropical moisture with bands of moderate to heavy showers remains focused over the eastern end of the state this morning, with Maui and the Big Island continuing to face the potential for heavy rain. The shortwave responsible for the most organized large-scale lift over the past couple of days continues to pull north and away from the state. As a result, rainfall intensity should steadily diminish somewhat through the day.

Elsewhere across the state, conditions are expected to remain somewhat quieter through the day, with only a few passing showers and overall lower rainfall chances, especially across Kauai and Oahu where drier air has already begun to fill in. This improvement, however, is expected to be temporary.

Guidance remains in good agreement showing another shortwave rotating through the broad upper trough northwest of the state later tonight into Sunday and then lingering into early next week. This feature is expected to once again strengthen large-scale ascent across the region while renewing the deep tropical moisture plume across the islands.

As a result, another round of widespread showers with periods of moderate to heavy rainfall appears increasingly likely beginning later tonight, first across the western end of the state, then expanding eastward through Sunday and potentially lingering into early next week.

Antecedent conditions are now the primary concern statewide. With soils remaining saturated, streams elevated, and some areas having already received substantial rainfall totals over the past 48 hours, flooding impacts will be much easier to realize with this next round of heavy rain. While some guidance continues to suggest an additional several inches may be possible over the duration of the next event, exact storm totals are less important than rainfall intensity and duration. Any period of intense rainfall rates could quickly lead to renewed flash flooding and rapid rises in streams. As a result, the Flood Watch is now in effect for all Hawaiian Islands through Monday afternoon.

One notable change heading into the extended period is the wind pattern. The strong southerly winds associated with the initial system over the past couple of days have weakened considerably, with mainly light and variable winds expected from today through much of next week. This lighter flow regime may allow heavier showers to linger over localized areas for longer durations, further increasing the flooding threat.

AVIATION

Issued at 902 AM HST Sat Apr 11 2026

A band of layered clouds, along with lingering showers, will reside over Molokai and eastward today. Less activity is expected over the western islands, other than diurnally driven afternoon interior showers over Oahu and Kauai. Windward Big Island could also see some afternoon shower activity. MVFR ceilings and visibility with isolated IFR conditions will be possible with any of the heavier shower activity. Expect sea and land breezes today for the western half of the state, while light to moderate S - SE winds remain for the eastern half.

A narrow band of moisture is expected to develop over the central portions of the island chain as early as tonight. This band of moisture will likely bring another round of heavier showers with isolated thunderstorms through Monday morning.

AIRMET Sierra is in effect for mountain obscuration above 1500 ft for Molokai, and for IFR conditions over Oahu and Lanai. IFR conditions will likely diminish with diurnal heating later this morning, but mountain obscurations may still remain throughout the day.

AIRMET Zulu remains in effect for moderate icing between 140-FL200 from Maui eastward to Big Island, but conditions will likely diminish later today.

MARINE

A low pressure system that is currently north-northwest of the main Hawaiian Islands continues to draw moisture across the area this morning. Showers are continuing across the central and eastern coastal waters, though upper-level support is expected to diminish today. A trough will linger in the vicinity of the islands into early next week, however, keeping winds lighter than seasonal average. Additional support for showers and isolated thunderstorms will return to the region by tonight into Sunday. East of the trough, moderate to fresh southeasterly winds will prevail, while winds west of trough will be light and variable, which may become southerly next week but remain generally light.

As southerly winds continue to decline today, surf along south- facing shores will return smoother, less choppy conditions. Additionally, the medium-period south swell will gradually decline through the weekend. By Tuesday, however, a new south swell will arrive, once again providing a boost to surf along south facing shores.

A moderate, short to medium-period northwest swell generated by the gale force low to the northwest will bring a boost to surf along north and west facing shores today. Another northwest reinforcement on Sunday will maintain this small to moderate surf through the weekend, followed by a decline in northwest swell energy next week.

Surf along east facing shores remains below seasonal average with lighter than average trade winds near and upstream of the islands forecast through next week.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through Monday afternoon for Hawaii.