textproduct: Honolulu

SYNOPSIS

A drier and less humid trade wind flow will continue to fill in over the state today. Shower activity will be focused across windward areas and will become less frequent, though leeward Big Island may still experience scattered briefly heavy showers in the afternoon. A tropical disturbance moving within the trade winds may bring increased humidity and showers again late Tuesday or Wednesday.

SHORT TERM UPDATE

A number of noteworthy features on infrared imagery this morning. To the northwest, a digging mid-level trough has triggered a convective flare-up as it feasts on the remnants of Lowell which itself is in the late stages of its baroclinic transformation. The lingering band of tropical moisture that has supplied the islands with humid conditions and spotty afternoon showers eased west of the islands overnight, and dewpoints will fall more uniformly into the mid to upper 60s during the next 24 hours as moderate trades advect a drier airmass into the area. The delayed arrival of said airmass over Leeward Big Island means today's afternoon convection may yet provide a localized threat for nuisance flooding over downslope areas of the North & South Kona Districts similar to yesterday.

Near 05N/150W, or about 1000 miles SSE of Hilo, a disorganized area of showers and thunderstorms persists. NHC offers a 20% chance of tropical development with this activity as it lifts toward the islands early next week. Regardless of the low probability of development, enhanced moisture and a modest boost in trade winds will accompany this feature as it lifts out of the deep tropics toward the islands early next week. GFS offerings of very humid conditions characterized by mid-70s dewpoints during the middle of next week look appropriate and will provide rich low-level moisture in support of enhanced trade wind shower coverage.

Eyes remain fixed on Tropical Storm Norbert, 2000 miles ESE of Hilo, as it slowly advances westward at 14 mph. Any potential arrival in the vicinity of the Hawaiian Islands is at least 10 days away. Forecast uncertainty is characteristically high at that lead time and it will be several days before confidence in impacts, or lack thereof, improves.

PREV DISCUSSION

Issued at 328 AM HST Fri Sep 11 2026 A drier air mass is slowly developing over the state on moderate trade winds. The bulk of a diffuse band of moisture has moved west of the islands, but some moisture remains hung up on Big Island and Kauai. Overnight, generally less than a quarter of an inch of rainfall has been measured on windward areas of these islands, and showers remained rather active over the South Kona District of the Big Island. Little rainfall occurred on windward Oahu and Maui County overnight, and dry leeward areas of these islands have been dry.

Expect a drier and less humid day over most of the island chain today. Moderate trade winds will push the bulk of the deeper moisture west of the islands, allowing leeward dew points to fall into the mid 60s and bringing relief from high humidity of the past several days. Typical light to moderate scattered showers are expected over windward areas, but rainfall accumulation will be low. Spotty afternoon showers, some briefly heavy cannot be ruled out on leeward Big Island and to a lesser degree on leeward Kauai.

Moderate trade winds will bring rather typical trade wind weather this weekend through early next week. A weak upper-level trough will linger over the area, keeping modest instability and a weak inversion over the state. As a result, there will be a chance of a few heavy showers over the Kona slopes of Big Island each afternoon and evening.

A tropical disturbance moving within the trade winds may bring increased humidity and showers again late Tuesday or Wednesday. Differences in timing and placement of this moisture persist between the GFS and ECMWF, which is keeping the details elusive at this point. This moisture could persist through Thursday of next week. Beyond that, there is significant uncertainty regarding the future location and timing of east Pacific Tropical Storm Norbert, which may be near the islands late in the week.

AVIATION

Moderate trades will prevail today and usher in isolated to scattered light showers to windward and mountain areas. The greatest coverage of low clouds and showers is concentrated around the Big Island this morning, where MVFR conditions are expected. Otherwise, besides in any brief passing showers, VFR conditions are expected to prevail across the remaining TAF sites.

AIRMET Sierra remains in effect for tempo mountain obscuration on the Big Island through the morning.

MARINE

Moderate to locally fresh northeast to east trade winds will continue through the forecast period. A tropical disturbance moving in from the trade winds may bring an increase of showers to the coastal waters by next week Tuesday into Wednesday.

Surf along south facing shores will gradually decline through the weekend as the small medium to long period energy slowly fades. Currently a low in the south pacific near Australia and New Zealand will bring the potential for a moderate long period swell for Hawaii late next week.

East facing shores will also remain at small to moderate through the forecast period due to the fresh to locally strong trade winds. Flat to tiny surf along north facing shores is expected through the forecast period.

FIRE WEATHER

Issued at 328 AM HST Fri Sep 11 2026 Fire weather risk will remain low the next several days due light to moderate winds and the effects of recent rainfall, even as afternoon relative humidity falls below 50 percent over many leeward areas. Inversion heights are expected to remain elevated or weak through Monday.

HFO WATCHES/WARNINGS/ADVISORIES

None.