textproduct: Honolulu

SYNOPSIS

Moderate to locally breezy trades will prevail through Tuesday, decreasing slightly by midweek, before easing to a more light and variable pattern by this weekend. Shower activity will be kept to a minimum as a cooler and drier airmass succumbs the Hawaiian Islands. A cold, upper-level trough makes an appearance late in the week and may slightly enhance trade wind showers, but any meaningful rainfall remains unlikely throughout the week.

DISCUSSION

An upper trough persists across the area as well producing thick cirrus clouds over the eastern end of the state. A 1032 mb surface high is centered far north of Hawaii driving fresh to strong trade winds across the area. Trades will focus low clouds and showers across windward areas, but accumulations will be light. 00Z sounding show precipitable water values of 0.78 inches at Lihue and 1.26 inches at Hilo (influenced by the high clouds), so showers will be limited by the relatively dry airmass.

Some guidance hints at a slight uptick in thunderstorm potential of around 10 percent over the Big Island, particularly along the southern slopes starting Tuesday afternoon. However, with moisture levels running exceptionally low, any storms that do form would likely be "dry" thunderstorms, producing lightning with little to no rainfall.

Looking ahead, the aforementioned high pressure system will gradually drift northeast and weaken around midweek. This will allow trades to ease, becoming lighter and more variable by Friday and into the weekend. At the same time, a weak upper-level trough may pass through late in the week. Even so, moisture remains limited, and any meaningful increase in rainfall still appears unlikely at this time. As always, we'll continue to monitor and refine the forecast as the pattern evolves.

AVIATION

Moderate to locally breezy trades will persist through Tuesday. Scattered showers caught up in the trades may bring brief periods of MVFR ceilings and visibility to mainly windward and mauka areas. Elsewhere, VFR conditions prevail.

AIRMET Tango is in effect below 8000 feet for moderate turbulence downwind of terrain. These conditions will continue well into Tuesday. AIRMET Tango is also in effect for moderate turbulence between FL240-FL360 through late this afternoon, but will likely be dropped by this evening as turbulence in the mid and upper levels weakens.

MARINE

Fresh to strong NNE trades persist through Tuesday, driven by strong high pressure N of the islands. Winds ease during the second half of the week as a trough develops E of the state and high pressure shifts east. Another trough will develop N of the state towards the end of the week which will further weaken trades. The Small Craft Advisory has been extended through tomorrow due to winds.

A moderate short period NNE (020 degree) swell generated by a gale low NE of the state will hold through tonight. Spectral analysis indicates energy with this swell is spread throughout the spectrum, but the vast majority is contained within the shorter period bins. Observations indicate surf is underachieving as longer period energy insufficient to generate High Surf Advisory (HSA) level surf. The HSA has therefore been dropped. However, the MWS for harbor surges remains in effect through Tuesday given little change in surf conditions anticipated during the next 24 hours.

For other shorelines, surf along east facing shores will remain choppy and short-period due to the strong trade winds, with some areas also being exposed to the incoming NNE swell. South shores will continue to see small pulses from the southern hemisphere over the next few days. A storm-force low developing southeast of New Zealand over the next few days could send a moderate south- southwest swell the following week.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Tuesday for all Hawaiian waters-