textproduct: Honolulu

SYNOPSIS

Limited showers windward and mauka into next week. More widespread rain develops over the western end of the state by Wednesday. Periods of heavy rain will be possible over and around Kauai and potentially Oahu.

SHORT TERM UPDATE

Prolonged period of moist SE flow has come to an end and benign moderate to breezy trades continue through Tuesday. Winds will perk up Sunday into early Monday as a weak tropical disturbance advances westward south of the area. However, nothing more than a modest coverage of windward and mauka showers is expected. No updates needed in the near term.

Attention for mid-week turns to a quick pattern transition from active tropics to a very early wet season type of system. A deep longwave trough extending from the mid-latitudes into the subtroipcs is modeled to develop during the first half of the week. Deep layer flow veers to the S/SE in advance of this trough drawing deep tropical moisture northward as early as Wednesday. A surface low will develop around 30N latitude northwest of Kauai with the western half of the island chain most likely to recieve meaningful rainfall. While guidance varies on important details, such as the position of the developing closed low and how long it persists, the end result seems to be an emerging threat for heavy rain and flash flooding one way or another during the second half of the upcoming week. The GFS allows trades to build in considerably faster, seemingly in response to its development of a suspiciously compact and intense surface low which quickly occludes and wraps westward under the upper low. The EC appears more realistic at this time and favors a flooding threat that could persist for a few days over Kauai and potentially Oahu. Forecast soundings suggest that while the dry slot will likely become established west of the islands, dry air entrainment within mid-level SW flow may still be a limiting factor, especially with respect to overall coverage of deeper convection. This system will be a focus of the afternoon forecast package.

AVIATION

Trade wind pattern will continue today, with isolated morning showers observed on a couple windward and mountain areas, with the most likely MVFR conditions at the Lihui and Hilo terminals through morning. Otherwise, VFR conditions should prevail the rest of the day.

No AIRMETs in effect.

MARINE

Gentle to fresh northeast to east trade winds has filled in today as high pressure strengthens gradually to the north. A Small Craft Advisory has been issued, in effect beginning this evening, when locally strong trades are forecast to develop for the windier waters and channels around Maui County and the Big Island. Locally strong trades may persist into early next week before high pressure to the north weakens again and winds start to diminish. By the middle of next week, troughing developing northwest of the islands may cause winds to veer out of the southeast once again.

A small background south swell will surf mostly steady along south facing shores through the weekend. A new small, long-period south swell, originating from a large fetch of gale force winds southeast of New Zealand earlier this week, is forecast to arrive beginning Sunday and peak Monday through Wednesday. This will push surf to slightly above seasonal averages for the first half of next week.

A small bump in surf along north-facing shores will decrease today as a small, short period north swell fades. Another small bump in north shore surf is possible early next week as a small, medium-period northwest swell arrives late Sunday and peaks on Monday. This will be followed by a slightly larger long-period northwest swell peaking on Wednesday, giving a good boost to north shore surf for mid-week. Surf along east facing shores will increase and become more choppy through tonight as easterly trades build back into the region.

FIRE WEATHER

Issued at 328 AM HST Sat Oct 3 2026

Drier air is expected over the weekend as light to moderate east- northeasterly trades return. Winds are expected to decrease early to midweek. Isolated showers will favor windward and mauka areas overnight into the early morning hours. Fire weather conditions will remain below critical threshold this week for both wind and humidity levels. Temperature inversion heights are around 5000-7000ft.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory from 6 PM this evening to 6 PM HST Sunday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters-Maalaea Bay-Pailolo Channel.