textproduct: Honolulu

SYNOPSIS

Breezy trades with light showers this evening. Statewide shower activity will mainly focus along windward exposures and upslope mauka with more organized cells passing over ridge tops and briefly wetting leeward communities. A plume of moisture moving south of the islands this weekend will likely clip the islands. This will increase rain chances, especially across Big Island, from late Saturday through early Monday.

SHORT TERM UPDATE

An evening of light to breezy trades as the islands fall between a 1025 mb high stationed off the U.S. mainland and lower equatorial pressure. Weak upper troughing just west of the state will spread mid to high layer clouds across the island chain from west to east through the overnight hours. Radar is fairly quiet with the greatest shower activity passing across windward Maui County and Oahu's nearshore waters and into the eastern-facing exposures of those islands. Afternoon soundings depict a very deep boundary layer, especially over the western islands, that appears moist enough to support continued pockets of passing easterly showers, the strongest cells putting down a quick couple of tenths of an inch upon their quick passage within the trade flow. The weekend will start off rather dry and warm, but a moisture-rich easterly air mass in association with a tropical wave or disturbance passing south of the islands near 10N will increase cloud cover and initiate more late Saturday through Sunday rainfall. The highest probability of precipitation is forecast to impact the Big Island and its surrounding eastern and southern waters early next week.

PREV DISCUSSION

Issued at 309 PM HST Fri Aug 7 2026

High pressure to our north will drive moderate to breezy trade winds through much of next week. An upper level ridge is currently moving overhead today along with drier air, allowing showers to stay light and isolated mostly to windward and mountain areas. This dry summertime pattern is expected to persist through tomorrow afternoon with CIMSS MIMIC precipitable water values estimated at around 1.2-1.3 inches. The 12Z balloon launch from last night showed precipitable water values around 1.3 inches as well.

Current satellite imagery depicts a weak tropical low with an associated tropical wave approximately 560 nm east- southeast of Hilo. Model guidance projects this low to weaken into a trough as it moves west- northwest. This trough will have a decent moisture profile associated with it when it arrives. Current CIMSS MIMIC precipitable water shows values of around 1.8 to 2 inches associated with it and it is expected to reach the Big Island by Saturday evening. Rainfall chances and humidity will increase for the Big Island and Maui County, then to a lesser extend, Oahu and Kauai Sunday into Monday. The most recent GFS model time- height cross section depicts the boundary layer inversion weakening, as conditions become more unstable, and moisture deepening up to at least 15,000 feet. Thus, from Saturday afternoon through Monday, embedded heavy rainfall will be possible for the Big Island and Maui County, especially for windward locations.

Though it is still too early to fine tune the forecast storm total amounts, typically wetter windward locations on Maui and the Big Island could pick up a couple inches of rainfall accumulation. Sufficient instability may exist for a rumble of thunder Sunday afternoon over the south or southwest slopes of Mauna Loa on the Big Island, but confidence is too low at this time to add to the current forecast package.

Typical summertime stable trade wind weather will return Tuesday through the end of the week with scattered showers mainly windward and mauka areas during the nights and early mornings.

Looking into the long range forecast for late next week, both Google Deepmind and global dynamic models are showing potential tropical cyclone development in the central Pacific. Details are far too early at this time but warrants further monitoring.

AVIATION

Moderate trades to slightly increase through tomorrow. Low cigs and SHRA likely over windward and mauka locations. MVFR conds possible otherwise VFR prevails.

No AIRMETs currently in effect, however AIRMET Tango may be needed for mod turb downwind of terrain as winds increase.

MARINE

Issued at 309 PM HST Fri Aug 7 2026

Moderate trades will continue to strengthen to fresh to locally strong speeds by this evening as surface troughing to the northeast weakens and a trough approaching from the southeast enhances the local pressure gradient. A Small Craft Advisory is in effect for locally strong trades across the typical windy channels and waters around Maui County and the Big Island. Fresh to locally strong trades will persist through at least the weekend, with the strongest winds over the southern portion of Hawaiian coastal waters as the surface trough nears.

Background medium- and long-period energy will continue to produce small surf along south-facing shores through tonight. A series of larger, medium- to long-period south swells will cause surf to trend upward along south- and west-facing shores from this weekend into early next week. A moderate, long-period south swell will peak near High Surf Advisory thresholds by midweek.

Along east-facing shores, trade wind swell will remain slightly below seasonal averages today before building this weekend in response to strengthening trades. Surf along north-facing shores will remain flat to tiny through the period, though a small, medium-period north swell could bring a slight bump on Sunday.

Due to a combination of peak monthly high tides and water levels running higher than predicted, minor coastal flooding is possible around the daily peak tide during the afternoon hours late this weekend into early next week along vulnerable shoreline areas.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Saturday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.