textproduct: Honolulu

SYNOPSIS

The high pressure ridge north of the islands will weaken through Monday as a strong cut off low pressure system deepens near the dateline. Wind directions will veer more southeasterly on Monday, then strengthening southerly winds from Tuesday onward. This next system is extremely strong for the Hawaii region and dangerous impacts are likely to develop statewide through much of next week. A combination of flooding, strong and gusty southerly winds, thunderstorms, and Big Island summit level snow and ice will threaten Hawaii from Tuesday through next weekend. Island by island impacts will be driven by both large scale troughs and smaller scale thunderstorm bands over the entire duration of this severe weather event.

SHORT TERM UPDATE

The satellite imagery this evening shows a strong low pressure system deepening near the International Dateline, drifting slowly towards the Hawaiian Islands. A significant band of thunderstorms continues to develop roughly 500 to 700 miles east to southeast of the low's center. A band of high level clouds even farther away from the low, shows embedded thunderstorms already developing within 200 to 300 miles west of Kauai.

Closer to the Hawaiian Islands we see some unstable cumulus clouds moving in from the east, producing periods of showers along the eastern slopes of the Big Island and Maui. These showers will bring a brief increase in clouds and showers to all islands through the early morning hours.

PREVIOUS DISCUSSION

Issued at 429 PM HST Sat Mar 7 2026

Stable weather conditions this afternoon as the islands remain under the subtle influence of weak surface ridging located just west of the state. The pressure gradient downstream of a large 1038 mb high has been taunt enough to produce breezy trades in the 10 to 20 mph range, occasionally exceeding 25 mph in gust through notoriously windy passages/valleys. Today's rain behavior was very light and spotty and confined to windward or interior upper terrain where the 24 hour rain accumulation winner was unsurprisingly Mt. Waialeale on Kauai with 1.25 inches. Overnight conditions will be mainly clear leeward, partially to overcast windward with the infrequent quick-hitting light trade shower. Tomorrow will be very similar to today as it relates to wind, cloud coverage and rain chances. The only minor change will the slightly greater coverage of measurable primarily windward rain as the boundary layer moistens up. The pattern begins to undergo change Monday, especially from Oahu westward, as a developing upper trough and its associated features begin to evolve far west northwest of the state.

Weather will undergo change late Monday as a deep upper level trough develops and deepens southward northwest of the islands. The trough will move east very slowly and begin to exhibit a negative tilt going into the middle of next week. This will initiate the next weather event that, because of its slow movement, will likely hang on for multiple days. The main threats will be periods of heavy rain that will create flash flooding, produce strong or severe storms and strong kona winds. NWP guidance indicates a strong jet streak nosing in from the west at mid week, along with a splitting jet with the base of the trough positioned over the western half of the state. The vicinity of the jet's more (upper difluent) left exit region may promote enhanced large scale ascent that is typically required for thunderstorm development. Along with this jet forcing, passing shortwave disturbances rotating around the base of the trough and cooling mid to upper layers, will be the ingredients that will increase chances for organized convection through mid to late week. Falling surface pressures northwest of the state will create a pressure pattern that will support strengthening south to southeast (kona) statewide winds. This will pull up a plume of rich tropical moisture across the region. As the trough lifts slowly northeast, very high precipitable water values of over 1.7 inches over the western islands Tuesday will expand east across the remainder of the state through Wednesday.

Lowering height falls, cooling air aloft, and increasing deep- layer shear will favor episodes of heavy rainfall with embedded thunderstorms. Broad south-southeast confluent flow running parallel with the upper terrain could support training and anchored convection. The potential for significant flooding remains alive through late in the week if and when heavier rain persists over the same locals (similar to what occurred over the Koolaus a couple of weeks ago). Flooding impacts could become more pronounced over time as soils become saturated and stream / reservoir levels rise. In addition to the flooding threat, thunderstorms could become strong, possibly severe, by the middle of next week. Another threat will be strong southerly winds atop ridge tops and along leeward slopes. Downslope winds Wednesday could become strong enough to throw light weight objects about, knock out power, cause minor structure damage, break off tree limbs and fall weaker rooted trees. Please monitor subsequent forecasts through Monday as details regarding the exact timing and location of the heaviest rain and strongest wind come into better focus.

AVIATION

Issued at 845 PM HST Sat Mar 7 2026

East southeast flow across Hawaii is expected to slightly weaken tomorrow. Scattered clouds will move in and bringing SHRA over southeast areas. MVFR conds possible in SHRA, otherwise VFR conds prevail.

AIRMET Sierra for mtn obsc is in effect for windward locations of Kauai, Oahu, Maui and The Big Island.

AIRMET Tango in effect for mod turb blw 080 downwind slopes (south across northwest facing). Expect this AIRMET to drop off in the morning. Directional LLWS possible at the PHOG/OGG runway Sunday afternoon.

MARINE

Issued at 429 PM HST Sat Mar 7 2026

Strong high pressure far northeast of the state will maintain fresh to strong trade winds through the rest of the weekend, with the strongest winds over the central and eastern coastal waters (with the exception of Maalaea Bay). A Small Craft Advisory remains in effect for these areas through 6 pm Sunday, though this may need to be extended for the typically windy channels and waters of Maui County and the Big Island through Sunday night. A front approaching from the west will ease the trades and shift them southeasterly on Monday, with the winds then becoming southerly and increasing to fresh to strong levels Tuesday through the rest of the week.

Surf along east facing shores will remain elevated and choppy through the rest of the weekend, trend downward on Monday, then lower below normal levels Tuesday through late next week.

A series of west-northwest swells will keep some small surf in place along north and west facing shores during the next 7 days, but surf will remain well below advisory levels. A small to moderate sized north swell is possible around Thursday and Friday of next week.

Surf along south-facing shores will remain small, with the exception of areas exposed to trade wind swell wrap. Rough and choppy conditions will develop Tuesday and continue through late week as southerly winds increase in advance of a front. A series of small long period south swells will also move through Monday through late week.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Sunday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Big Island Windward Waters-Kaiwi Channel-Maui County Leeward Waters-Maui County Windward Waters-Oahu Windward Waters-Pailolo Channel.