textproduct: Honolulu

SYNOPSIS

A powerful kona storm will impact the state through this weekend resulting in potential flash flooding, damaging winds, and strong to severe thunderstorms. Impacts will generally be felt over the western end of the state first and then spread east with time. The peak of this event is forecast to be Friday and Saturday.

SHORT TERM UPDATE

Issued at 750 AM HST Wed Mar 11 2026

Event kicks off with a rather poorly modeled batch of initial rainfall that developed overnight within a weakly forced corridor of SSWly warm advection. This area of rainfall is characterized by uniformly distributed rain rates of of 1"/hr or less except within embedded convective elements where rates up to 1.5"/hr are noted. 12-hour rainfall amounts thus far range top out at 5.81" at N Wailua Ditch on Kauai and several gauges around 2" on Oahu with a peak value of 4.51" at the Poamoho gauge. Rain has since spread into Maui County where similar values can be expected this morning before this initial wave of forcing lifts off to the north leaving behind less organized light stratiform rainfall in its wake.

Despite the anticipated lull in activity by late this morning, an upper wave pivoting through the area and outstanding left exit jet will provide strong background forcing for the balance of the day. Surface convergence will be hard to come by, but strong forcing will make the most of the weakly stable background environment suggesting disorganized pockets of moderate to heavy rain will be possible through the day. However, weakly convergent SW flow is observed southwest of Oahu and convection is currently developing along it. SW flow will steer this convection toward Oahu with an estimated arrival time of late morning to around noon and will likely carry higher rain rates than seen this morning. Convection then potentially advances into Maui County this afternoon. The wind field has yet to ramp up, so any associated wind gusts are expected to be sub-severe. Kauai likely remains in a relative lull from now through late tonight, though periods of disorganized convection carrying elevated rain rates will be possible throughout this time.

The next wave of showers in the sequence will begin to materialize well south of Kauai midday today under stellar upper level jet support and continued dyanmic forcing aloft. SW winds will likewise begin to strengthen during this time with 35-40kts modeled at 850mb and southerlies at the surface approaching 20kts by early Thursday morning. 500mb temps falling to around -13C and 700-500mb lapse rates approaching 7C/km over the western end of the state by the predawn hours Thursday suggest potential for heavy rain and thunderstorms focusing over Kauai, Oahu or both by sunrise Thursday, but most likely later in the morning.

PREV DISCUSSION

A high-impact weather event continues to unfold across the Hawaiian Islands as a powerful kona low remains positioned northwest of the state. Radar imagery early this morning shows bands of showers lifting north across the state, with peak rainfall rates ranging between 1 and 2 inches. Several streams have already become elevated following the overnight rainfall, and flooding remains possible where heavier showers persist.

The larger-scale pattern remains largely unchanged. A broad upper-level low northwest of the islands continues to deepen while an associated upper trough becomes increasingly negatively tilted as a strong jet streak, with core winds of 100 to 140 kt near 250 mb, digs southeastward along its western flank. As this trough amplifies and gradually expands toward the islands through midweek, the state will increasingly fall beneath the jet streaks left-exit region, supporting enhanced divergence aloft and large-scale ascent across the region.

At the surface, a broad area of low pressure will remain well northwest of the islands in response to strong upper-level height falls. Central pressures are forecast to remain near 990 mb while maintaining a southerly to southeasterly flow across the state. This flow will continue to transport deep tropical moisture northward across the island chain, with precipitable water values remaining near or above two inches.

The combination of strong upper-level forcing, deep moisture, and persistent southerly flow will support repeated rounds of showers and thunderstorms through the remainder of the week. Smaller disturbances rotating through the upper trough will likely help focus additional rainbands across portions of the state, raising the potential for training rainfall and locally intense rainfall rates, particularly in terrain-favored areas.

In addition to the rainfall threat, strengthening south to southwest winds may develop Friday into the weekend as the pressure gradient tightens between the developing low to the northwest and high pressure to the northeast. If this materializes, strong and potentially damaging kona winds will be possible, including localized downslope winds capable of downing trees and power lines.

Environmental conditions will also periodically become favorable for strong to severe thunderstorms over the next few days, particularly Friday into Saturday. Instability combined with strong deep-layer wind shear during this period will support thunderstorms capable of producing damaging winds, large hail, and possibly a tornado.

For the summits of the Big Island, colder air associated with the upper trough will periods of heavy snow with significant accumulations later this week and into the weekend, which has prompted the issuance of a Winter Storm Watch this morning.

AVIATION

Issued at 826 AM HST Wed Mar 11 2026

Moderate to heavy showers will persist through much of the day today across the state with prolonged periods of MVFR conditions with tempo IFR/LIFR conditions at times under heavier showers. Increasing instability today may allow for isolated thunderstorms to develop, but confidence was not high enough to mention TS specifically in any of the TAFs.

AIRMET SIERRA remains in effect for mountain obscuration for all of Kauai, Oahu and Maui Counties, as well as the south and southeast portions of the Big Island.

AIRMET ZULU remains in effect for light icing from Kauai through Maui County for FL 130-240.

AIRMET TANGO is in effect for moderate turbulence over Kauai and Oahu as the VAD wind profile shows strong southerly winds have spread across the area.

AIRMET TANGO is also in effect across the state for moderate turbulence associated with this Kona low. Upper level turbulence is generally expected to decrease towards the evening with the exception of areas with thunderstorms.

MARINE

A powerful kona storm will result in heavy rain, thunderstorms, and rough seas to the islands and adjacent coastal waters through the rest of this week. Early this morning, bands of heavy rainfall are observed on radar imagery moving from south to north within a southerly wind regime across the Hawaiian waters, especially across leeward waters. Fresh to locally strong southerly winds were observed in a late evening advanced scatterometer pass, and this fresh to locally strong southerly flow will continue through the day today. A Small Craft Advisory (SCA) remains in effect for the waters surrounding Kauai, and both leeward and windward waters of the Big Island have also been added to the SCA with this morning's updates based on the latest ASCAT pass and hi-res model guidance. After a brief lull in southerly wind speeds tonight into Thursday, reintensification will cause winds to approach, or possibly reach, gale-force speeds for portions of the area as early as Thursday night or Friday, and lasting into the weekend.

A series of small, medium- to long-period west-northwest swells will bring small surf to north and west facing shores through the rest of the week. The first of these will peak today, resulting in a slight bump in surf along north and west-facing shores. This swell will then decline before the next west-northwest swell arrives on Friday. Additionally, a small, medium- period north swell is also expected to arrive Thursday night into Friday.

Choppy surf along east-facing shores will continue to trend downward, falling below seasonal levels today as winds veer southerly. With the shift of wind direction, surf along south-facing shores will increase, becoming rough and choppy. Later this week, another round of stronger southerly winds Friday into the weekend will cause south shore surf to build further, likely reaching advisory levels. A series of small, long-period south swells will also move through.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through Saturday afternoon for Central Oahu-East Honolulu-Ewa Plain-Haleakala Summit-Honolulu Metro-Kahoolawe- Kauai East-Kauai Mountains-Kauai North-Kauai South-Kauai Southwest-Kipahulu-Koolau Leeward-Koolau Windward-Lanai Leeward- Lanai Mauka-Lanai South-Lanai Windward-Maui Central Valley North- Maui Central Valley South-Maui Leeward West-Maui Windward West- Molokai Leeward South-Molokai North-Molokai Southeast-Molokai West-Molokai Windward-Niihau-Oahu North Shore-Olomana-South Haleakala-South Maui/Upcountry-Waianae Coast-Waianae Mountains- Windward Haleakala.

High Wind Watch from Thursday evening through Sunday afternoon for Big Island Summits-Haleakala Summit.

Flood Watch from 6 PM HST this evening through Saturday afternoon for Big Island East-Big Island Interior-Big Island North-Big Island South-Big Island Southeast-Kohala-Kona.

Winter Storm Watch from Thursday evening through Saturday afternoon for Big Island Summits.

Small Craft Advisory until 6 PM HST this evening for Big Island Leeward Waters-Big Island Windward Waters-Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters.