textproduct: Honolulu

SYNOPSIS

Moderate trades will build to breezy levels Thursday as weak troughing near the state dissipates and a new surface high develops north of the state. Expect limited mainly windward and mauka clouds and showers into next week. Showers should increase slightly in coverage and strength late Friday into the weekend as winds become slightly stronger.

DISCUSSION

Radar and satellite show scattered showers and mostly cloudy skies across the Puna and Ka'u districts of the Big Island this afternoon. Skies were partly to mostly sunny with isolated showers over eastern Maui, and mostly sunny elsewhere. Winds were generally out of the east to northeast at 5 to 15 mph, except for locations downwind of terrain, where light west winds were common.

Forecast models are in good agreement that a series of surface high pressure systems will move west-to-east across the northern Pacific, giving us an extended period of trade winds. By early next week, surface troughing may develop as a strong upper level ridge develops to our north. This troughing could lead to an increase in showers from late in the weekend into early next week, especially on the eastern end of the state. Confidence is not high at this time, as models are not in agreement on how much moisture may move into the region. Otherwise, expect a typical trade wind regime, with mainly windward and mauka showers, most numerous at night.

AVIATION

Moderate trades hold through tonight before strengthening to breezy levels Thursday. An area of enhanced moisture will move from east to west across the state tonight, increasing clouds and showers for windward and mauka areas. Brief MVFR ceilings may occur within better organized showers, but mostly VFR conditions should prevail.

AIRMET Sierra has been issued for windward areas of the Big Island as an area of clouds and showers fills in this evening. Maui may need to added to this AIRMET later this evening.

MARINE

Surface high pressure far northwest of the islands will move closer tonight and Thursday, then build as it moves to the north then northeast of Hawaii on Friday. As a result, trade winds will gradually increase to fresh to locally strong levels over the next couple of days. A Small Craft Advisory (SCA) has been issued for the typically windy waters around Big Island and Maui starting Thursday. A stronger surface high will pass far north of the islands late Saturday and Sunday, likely increasing trade winds and possibly necessitating an expansion of the SCA to additional waters. Elevated trade winds will persist into early next week.

The current northwest swell will continue a gradual decline through Thursday, followed by a moderate north-northwest swell Friday through the weekend. The current swell has lowered to around 4 ft at 12 to 13 seconds this afternoon and will slowly fall through Thursday. The next swell will be from the north- northwest and will arrive early Friday. Surf along north and west facing shores should top out around seasonal average during the peak of the swell Friday afternoon and Saturday, then slowly decline late Saturday and Sunday as the dropping swell shifts more northerly and a smaller overlapping northwest swell arrives. Both swells will fade early next week.

Surf along south facing shores will briefly fall near or just below seasonal average as the current south swell continues a slow decline tonight. A new long-periond south swell will build Thursday and may push south shore surf back above seasonal average through Friday. The swell will slowly decline Saturday through early next week.

Surf along east facing shores will remain small through Thursday and will steadily increase Friday as trade winds strengthen over the region. Rough trade wind swell will produce east shore surf above seasonal average Saturday through early next week.

FIRE WEATHER

Moderate trade winds will strengthen to breezy levels Thursday. Dry air will keep RH levels at near-critical values each afternoon for parts of the state Friday through Sunday. RH values are expected to increase from Monday through the middle of next week. Winds will remain below critical thresholds. Inversion heights today should range from about 5,000 to 6,000 ft through Thursday.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory from 6 AM Thursday to 6 PM HST Saturday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters-Maalaea Bay-Pailolo Channel.