Area Forecast Discussion for Hawaii

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Issued: May 05, 2016 4:00 PM HST

Synopsis
A cold front approaching the region from the west northwest will cause light southeast wind flow through Friday. This will allow the sea breeze convergence over the islands to trigger cloud build ups and locally heavy afternoon showers Friday afternoon. The front is expected to weaken to a surface trough as it reaches Kauai Friday night, with trades focusing remnant moisture over windward slopes Saturday into next week.

Discussion
A cold front located about 600 miles to the west northwest of Kauai and is approaching the islands. A ridge axis lies 200 miles north of Kauai. These two features are resulting in light southeast wind flow across the state, and dominating sea breezes over the islands. Visible satellite and radar show cloud build ups and some showers over the island interiors this afternoon associated with the sea breeze convergence, with Kauai seeing the most rain this afternoon.

For tonight, expect decreasing showers over the islands as the land breezes set in, especially over the leeward sides of the islands. Moisture may funnel in over the islands later tonight from the south or southeast and bring a chance for rain. Most of these showers will focus over the windward and southeast slopes.

For Friday, sea breezes will again set up and bring increasing clouds and showers through the day. Locally heavy rain will be in the forecast again in the afternoon as the cold front to the west northwest draws more moisture over the state. The southeast background flow will produce muggy conditions and bring vog onto the smaller islands tonight.

The front will weaken to a surface trough as it reaches Kauai Friday night. As this trough moves eastward across the island chain through Saturday, northeasterly trades will spread across the state. These northeasterly winds may be locally breezy, especially over the western end of the state on Saturday, and will funnel showers mostly across the windward and mauka areas.

The winds will eventually weaken to moderate breezes Sunday and Monday, before boosting up again Tuesday as a high builds northwest of the area. The remnant moisture associated with the former front/trough will also likely produce an extended period of wet trade wind conditions from Sunday into the middle of next week. Both the long range GFS and ECMWF models indicate the trades will focus showers mainly over the windward sides of the islands from Oahu to the Big Island.

Aviation
The front northwest of Kauai will continue to advance towards the state, pushing the ridge south onto the islands. The resulting light background SE flow has allowed for sea breezes to develop, along with interior clouds and isolated showers. Overall terminals should remain predominately VFR this evening. Expect most land areas to begin clearing as land breezes take hold.

An area of increased moisture is moving towards the Big Island. The north and east sides of the Big Island will likely experience some prolonged periods of MVFR conditions tonight as the band of moistures moves through. The enhanced moisture will eventually make its way to the smaller islands very late tonight, increasing the change for periods of MVFR conditions mainly along north and east sides. There are no airmets posted at this time for mountain obsc, but they can not be completely ruled out tonight and will be posted as needed.

Marine
A small west northwest swell will persist through Friday. A reinforcing small north northwest swell will arrive Saturday and last through the weekend.

A small south swell will maintain background surf along south facing shores tonight. A long period south swell will arrive Friday and peak late Saturday above the seasonal south swell average, and then slowly subside into early next week. While surf will be elevated, surf heights are expected to remain just below the high surf advisory criteria along south facing shores this weekend.

Trade winds building in this weekend and next week will marginally boost surf heights along east facing shores. No high surf or small craft advisory are in effect, or expected, through Friday.

Watches/Warnings/Advisories
None.


DISCUSSION/MARINE...FOSTER

AVIATION...EATON