textproduct: Honolulu

SYNOPSIS

A weak surface trough will gradually move east to west across the islands tonight through Saturday, resulting in relatively light winds and a combination of trade showers and sea-breeze showers (during the afternoons). As this trough dissipates, trades will build in stronger Saturday night through Sunday, and even stronger trades are forecast for next week from Tuesday onward.

DISCUSSION

Radar show showers, mainly windward and mauka, over Kauai and Niihau this afternoon. An increase in showers across the Big Island is expected soon, and is likely also on windward (northeast) Maui and Molokai. Satellite indicates low clouds over or near the higher terrain on each island, along with wispy high clouds streaming in from the southwest. These higher clouds should continue through the night, while the lower clouds will diminish in most areas after sunset.

A weak surface trough was located between Maui County and the Big Island as of 3 PM HST this afternoon. This feature will slowly drift westward, reaching Kauai Sunday. Trade winds will build in behind this trough, moving in from east to west through this weekend. Wind speeds will initially be light to moderate, but will become moderate to occasionally breezy early next week. This trough will keep winds weak enough to allow for sea-breeze showers to occasionally develop over leeward areas, even as trade winds build in and bring their typical windward-focused showers.

While that is occurring at the surface, the flow aloft will change significantly. We will transition from weak troughing to our north this weekend to the rapid development of a closed ridge to our northwest by Monday. This ridge will become elongated along an east-west axis and remain with us all next week. Its presence will keep a surface ridge in place, allowing the trades to blow at least through the end of next week, and likely longer. This means trade wind showers, mainly windward and mauka, will be the rule for quite a while. There will be occasional fluctuations in available moisture throughout this period, and these will result in periods of enhanced shower activity from time to time. The timing is impossible to nail down more than a few days in advance.

AVIATION

Local sea breezes will gradually become light to moderate trade winds tonight, then eventually locally breezy tomorrow through the weekend. Clouds and showers over leeward and interior areas this afternoon will likely decrease tonight and trade winds will push the showers over the typical windward and mountain areas.

VFR conditions will mostly prevail, however some brief MVFR conditions are possible in any showers.

AIRMET Sierra for mtn obscuration is in place over Kauai and Oahu due to lingering showers, this AIRMET could stay in place for Kauai for much of the night, as model guidance indicates that moisture could linger through the night and tomorrow morning. Also there will be potential for AIRMET Tango for low level turbulence once the trade winds pick up.

MARINE

A weak trough northeast of the islands will keep trade winds light to locally moderate across all local waters tonight. However, a strengthening surface ridge northwest of the state will bring a return of moderate to locally fresh trades by Sunday. A Small Craft Advisory may be needed for the typical windy waters surrounding Maui and the Big Island as early as Saturday night. Trade winds will continue to strengthen as the high expands eastward early next week.

A declining moderate, medium-period, northwest swell will continue to bring elevated surf to north and west facing shores tonight. This swell and associated surf will slowly fade through the weekend. A new small, medium-period northwest swell arrives on Saturday, leading to a small bump in north and west shore surf on Sunday. For the first half of next week, surf will be small with the lack of any significant northerly swell energy.

A small, long-period south swell should provide a small bump in south shore surf through Saturday. Sunday into next week, background swell energy will keep small surf along south-facing shores.

Surf along east-facing shores will remain below normal this weekend, but will gradually increase through next week as trade winds gradually strengthen.

HFO WATCHES/WARNINGS/ADVISORIES

None.