textproduct: Honolulu

SYNOPSIS

Flash flooding will be possible over island interiors this afternoon and over windward and mauka areas tonight as moist and unstable trades build into the area. Trades then persist through mid-week becoming increasingly stable with time.

SHORT TERM UPDATE

Issued at 906 AM HST Sun Feb 22 2026

Cold northwest flow aloft supports moderate instability noted on this morning's soundings out of Lihue and Hilo. CAPE on the order of 1000 j/kg is forecast to develop over island interiors by this afternoon as 500mb temperatures fall to around -15C and 700-500mb lapse rates approach 7C/km. The environment will be weakly or even neutrally forced aloft as the bulk of PV advection already occurred yesterday. Instead, the islands reside in a favorable thermodynamic environment that will be particularly sensitive to developing low- level convergence, namely among emerging sea breeze boundaries this afternoon. Deep, slow-moving convection/tstorms will therefore be possible over island interiors. Confidence is hindered by lingering high clouds over portions of Oahu which may limit sea breeze development, but daytime heating is in full swing on Kauai, Molokai, and Maui. Thunderstorms may develop over the higher terrain of the Big Island this afternoon where they are considerably less likely to result in a flash flooding threat.

Trades then return tonight as the environment remains weakly forced overall. The mechanism for low-level convergence will shift to terrain and will therefore refocus the flash flooding threat over windward and mauka zones for tonight. Trades will gradually strengthen, becoming breezy by early morning Wednesday which will lead to decreasing convergence and increasingly progressive shower motion with time. However, at least the first half of the night will see rather slowly building trade winds and correspondingly slow-moving convection embedded within. A Flood Watch has therefore been issued for Kauai, Oahu, Molokai, and Maui.

AVIATION

A trough just north of the islands will keep winds light and variable today, with sea breezes developing in most areas. Showers and thunderstorms will favor areas near the coast through the morning hours, then transition over to interior areas this afternoon. High pressure building to the distant north, will then push the trough back southward through the state tonight and Monday, bringing another round of heavy showers and a few thunderstorms and a return of breezy and gusty trade winds. Predominantly VFR conditions will prevail at most of the TAF sites today, with brief reductions to cig/vsby possible in showers and thunderstorms. MVFR cigs/vsbys will become more common tonight as the trough and associated heavy showers return to the islands.

AIRMET Sierra remains in effect for mountain obscuration on the Big Island. Conditions should improve here later this morning.

AIRMET Tango remains in effect for moderate upper level turbulence across the entire state. These conditions are expected to remain in place through the day.

AIRMET Zulu continues to mention light icing from 12 kft to FL240 across the entire state. Conditions are expected to improve later this morning.

MARINE

A strong high pressure system building far north of the Hawaiian Islands continues to push a low level trough towards the state. This trough will continue to block large scale trade winds today with light and variable winds for all waters. Land and sea breezes expected for near shore waters of all islands. The low level trough will move into the islands from the north tonight through Monday. Fresh to strong trade winds and moderate to heavy rain showers and isolated thunderstorms will blow in across the region. Trade winds weaken again and veer more southeasterly from Thursday into Friday as another cold front approaches the island chain from the west.

Surf along exposed north and east facing shores will quickly build through the day Monday as a long period north-northeast (010-020 degree)swell from a broad storm force low develops off the northwest Pacific coast this weekend. A large area of northerly gales between this system and a 1040 MB blocking high will continue to drift southward. Surf heights will exceed advisory levels by Monday afternoon, possibly reaching low end warning levels by Monday night, for exposed north and east facing shores lasting through Tuesday. Although a gradual downward trend is anticipated by Wednesday, additional pulses from this same system will keep surf above advisory levels along east facing shores through much of the week. This swell direction will bring surf into some typically protected areas such as Kua Bay, West Maui, and exposed shores of Lanai.

Other impacts from this north-northeast swell direction will include overwash along vulnerable sections of coastline and roadways by Monday night during the early morning high tide cycles. Mariners can also anticipate harbor surges at Kahului and Hilo.

Surf along exposed west facing shores will rise early next week as a long-period northwest swell arrives from a recent broad storm force low over the far northwest Pacific. This swell will slowly fade into Wednesday.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch through late tonight for Kauai, Oahu, Molokai, and Maui.

High Wind Warning until 6 AM HST Monday for Big Island Summits.