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Issued: Jun 15, 2019 8:05 PM HST

Synopsis
A fairly dry trade wind weather pattern will continue through the middle of next week. Clouds and isolated to scattered showers will remain in the forecast over windward and mountain areas favoring the overnight and early morning hours. Little to no rain is forecast over leeward areas.

Discussion
Another extended period of fairly dry trade wind weather remains in the forecast through next week. Subtle changes in the strength and position of the high pressure ridge north of the islands will result in slight adjustments to trade winds and windward shower coverage over the next seven days. Expect moderate to breezy trade winds to continue on Sunday with limited shower activity in a stable and mostly dry weather pattern.

In the big picture, the subtropical ridge north of the islands continues to produce moderate to breezy trade winds on Sunday. A strong high pressure ridge aloft will keep clouds and showers to a minimum with trade wind subsidence inversion heights around 5000 to 6000 feet. A long wave trough remains anchored over the Central Pacific basin. Subtle changes in the intensity of this long wave trough will impact the strength of the ridge north of the islands, modifying the trade wind direction and speed for the upcoming work week.

On Monday and Tuesday, the long wave trough deepens weakening the subtropical ridge north of the islands. These changing large scale pressure patterns will place the Hawaiian Islands along the southwestern edge of the surface ridge axis, causing wind directions to veer towards the southeast direction. At the same time step, the upper level ridge weakens as a trough drifts over the state. Wind speeds will weaken slightly on Monday and Tuesday with modified land and sea breezes forming along sheltered leeward slopes. The upper trough will decrease atmospheric stability allowing for more scattered windward and mauka showers favoring the overnight and early morning hours. Trade wind subsidence inversion heights will rise into the 7000 to 9000 foot range by Monday night.

Wednesday through Friday, the surface ridge north of the islands builds slightly and trade winds back towards a more easterly direction. The subtropical jet stream will develop over the islands producing high cirrus cloud ceilings across the state. A building upper level ridge will bring another round of more stable conditions with subsidence inversion heights falling back down into the 5000 to 7000 foot range on Wednesday and Thursday. A weak upper trough will bring a return to more scattered windward and mauka showers from Friday night into Saturday morning.

Aviation
Surface high pressure will remain to the northeast of Hawaii, providing moderate to locally strong trade winds to the area. Passing low clouds will affect windward and mountain areas of the islands at times, bringing some showers. Mainly VFR conditions will prevail, though windward and mountain areas may see brief MVFR ceiling and VIS.

No AIRMETS are expected through early Sunday, but the potential for AIRMET Tango for low-level turbulence continues due to the more robust trade winds.

Marine
High pressure far northeast of the state will maintain fresh to locally strong trades through the middle of the coming week. Winds may veer east-southeasterly Monday into Tuesday as a weak trough develops far west of the state. A Small Craft Advisory (SCA) is in effect for the typically windy waters around the Big Island and Maui through early Monday morning. This will likely need to be extended at least into Wednesday.

Elevated surf is expected along south facing shores through early Sunday morning. Due to the swell still holding strong into this evening, the High Surf Advisory has been extended through tonight. For next week, we should see several reinforcing south- southwest swells for the first half of the week with surf heights around the summer average through the middle of the coming week.

A reinforcing northwest swell is filling in tonight and will continue to produce surf in the small to moderate range along north facing shores through Sunday. Additional pulses of tiny northwest swell are expected through next week. Surf along east facing shores will remain small through the weekend, then rise early next week.

Watches/Warnings/Advisories
High Surf Advisory until 6 AM HST Sunday for all south facing shores.

Small Craft Advisory until 6 AM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.


DISCUSSION...Bohlin

AVIATION...Hui

MARINE...Kinel