Area Forecast Discussion for Hawaii

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Issued: Jun 27, 2016 4:00 PM HST

Synopsis
High pressure north of the area will maintain trade winds through the holiday weekend. Ridging aloft will keep the atmosphere dry and stable through tomorrow, so rainfall will be light and confined to mainly windward areas. A low aloft will move south over the area Wednesday and make the atmosphere unstable, so showers may become more active through Thursday. On Friday the atmosphere will become more stable and much drier and rainfall will become sparse. A strong high building northeast of the area will bring windy weather over the holiday weekend.

Discussion
A strong 1030MB high 930 miles north northwest of Kauai at 36N 166W will move south slowly and weaken over the next few days. This high will keep trade winds breezy through tonight. A ridge aloft southwest of the area will keep the atmosphere fairly stable and dry through tomorrow, so rainfall should remain rather light.

The global models are in good agreement showing a trough digging southeast toward the area tomorrow. A low aloft is forecast to form north of Kauai tomorrow night, then move southwest slowly through Thursday night. The low will bring colder air aloft, resulting in the airmass over the islands becoming more unstable. An area of low level moisture about 350 miles east of the islands will be moving over the islands by Wednesday so the atmosphere will also be getting more moist. Showers will likely become more active Wednesday and Thursday and thunderstorms may be possible.

Starting Thursday night, the low aloft will move off to the west and ridging aloft will build over the islands from the southeast. As that happens, the atmosphere over the islands will turn drier and more stable, and showers will become less active. A strong surface high will build far northeast of the state by next weekend. Trade winds will strengthen and it may be quite windy through the Independence Day weekend.

Aviation
VFR will prevail, but brief MVFR ceilings and visibilities will be possible in passing SHRA over windward areas, with PHTO the most likely TAF site to be impacted. AIRMET SIERRA for MTN OBSC may need to be issued at times.

AIRMET TANGO is in effect for mechanical turbulence immediately south through west of mountains on all islands below 8000 feet and the AIRMET is likely to stay up through at least this evening.

Marine
A strong high far northwest of the area will produce strong trade winds in the windy zones around the Big Island and Maui tonight, so a Small Craft Advisory remains in effect for those areas. We expect to drop the advisory tomorrow. A new high will build northeast of the area during the second half of the week. That high is forecast to become unusually strong, and could push the trade winds up near gale force in the windier areas over the holiday weekend.

Surf will remain below High Surf Advisory (HSA) levels along all shores for at least the next few days. The current south swell will persist through tomorrow. After that, smaller than normal surf is expected along south facing shores through the holiday weekend. Fairly small but rough surf along east facing shores will subside tomorrow as the trade winds weaken. Surf will rebuild along the east facing shores over the weekend as the trades strengthen again.

Fire weather
Starting Thursday night, the atmosphere over the islands will become quite stable and very dry air will spread over the area from the east. Wind speeds will increase significantly by the weekend as a strong high builds north of the islands. The low humidity and strong winds will boost the fire danger over the weekend.

Watches/Warnings/Advisories
Small Craft advisory until 600 AM for the Pailolo and Alenuihaha Channels, Maalaea Bay and waters south of the Big Island.


Donaldson