textproduct: Honolulu

SYNOPSIS

After a prolonged stretch of impactful kona weather and heavy rainfall across the state, a gradual return to a more typical northeast trade wind pattern is expected by midweek. A lingering moisture axis over the eastern end of the state, combined with an upper trough, will support periods of locally heavy showers and storms today, mainly over Maui and the Big Island. Thereafter, a drier and more stable trade wind pattern is expected from late week through the weekend and into early next week.

DISCUSSION

Latest satellite imagery shows a narrow and persistent convergent band over and upstream of the Haleakala windward slopes of Maui that continues to fuel heavy showers this morning (over 4 inches of rain in the past few hours as of 3 am HST). Elsewhere, mostly dry northeast trade wind conditions prevail across the island chain. Dewpoints have dropped into the lower 60s across the western end of the state, resulting in noticeably cooler and more comfortable conditions compared to recent days.

The past several days have been exceptionally wet across portions of the state, particularly from Oahu through the Big Island. Peak rainfall totals over the past 5 days have generally ranged from 15 to 25 inches in some areas, with a preliminary statewide peak of 25.73 inches observed at Kaala on Oahumost of which fell Thursday night into Friday. This recent period of heavy rainfall has led to saturated soils and elevated streamflows, leaving areas very sensitive to additional rainfall.

Looking ahead through midweek, a lingering axis of moisture over the eastern end of the state combined with cold temperatures aloft (decent mid-level lapse rates) associated with a departing but still influential upper trough will maintain the potential for locally heavy showers and storms today, especially across Maui and the Big Island. Given the saturated ground conditions, even modest additional rainfall could lead to renewed runoff and localized flooding concerns. As a result, a Flood Watch has been extended through this afternoon for Maui and the Big Island.

Elsewhere, more stable conditions are expected as trade winds strengthen and drier air filters into the region. By Wednesday and beyond, the state should transition into a more typical trade wind pattern featuring passing windward showers and generally drier leeward conditions. This pattern is expected to persist through the remainder of the week and into the weekend, consistent with broader guidance indicating decreasing moisture and a return to climatological conditions.

AVIATION

High pressure building into the Hawaii region from the northwest will keep moderate to locally breezy trade winds in the forecast for the next few days. An upper level trough will keep periods of passing showers over the windward mountains of all islands with MVFR conditions possible in showers.

Expect MVFR conditions with periods of showers forecast across the state favoring windward and mountain areas.

AIRMET Sierra for mountain obscuration remains in effect for north and east sections of Kauai Oahu, Molokai, Lanai, Maui, and windward Big Island.

MARINE

Upper level energy diving down into a trough lingering near Big Island will keep the chance of eastern water showers and isolated storms alive through the day. High pressure building far north of the area will result in strengthened northeasterly winds across the local nearshore waters. A Small Craft Advisory is in effect for all coastal waters due to these increasing northeasterlies and elevated seas. Winds will be strongest through Wednesday but should ease Thursday. Moderate trades will close out the week.

A fading north northwest swell will be overlapped by a reinforcing pulse of medium period north northeast swell. This swell will peak this afternoon and evening and then decline Wednesday. Another small, medium period west northwest swell will arrive Thursday, peak Friday, then decline during the weekend. Aside from areas along east shores exposed to the northerly swell, short period energy from rebuilding trades will increase to near seasonal averages tonight and Wednesday and then hold into the weekend. A small south southwest swell will decline today and then fade Wednesday. A short-lived pulse of small south southeast swell will be possible Wednesday through Friday, and a small south southwest swell could arrive Friday into the weekend.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through this afternoon for Maui and the Big Island.

Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters-