Daily Weather

Mar 15, 2015 5:00 AM HST

Synopsis
Trade winds will weaken today, with light and variable winds expected from late tonight through Wednesday. Mostly dry weather will continue through Wednesday, with just a slight chance of light showers. In addition, the air mass will gradually warm, and the recent run of unusually chilly weather will end. Trade winds will increase Wednesday night and Thursday, bringing increased windward showers. A breezy and relatively wet trade wind pattern will then persist into next weekend.

Discussion
High pressure centered about 650 miles NNW of Oahu will migrate steadily eastward over the next 12 to 36 hours, and become established far NE of the islands by Monday. An associated surface ridge extending westward from the high will be several hundred miles N of the islands by this evening, supporting a trade wind flow that will be gradually easing today and tonight. The ridge will move S to a position just N of Kauai by Monday, and a light wind pattern will develop over the islands and surrounding waters. The light winds will allow island-scale land and sea breezes to prevail.

The ridge will be shunted southward as a slow-moving front approaches the area from the NW. The light wind pattern will continue until Wednesday night/thursday, when a new high will build N of the area, bringing stronger trades for the latter half of the week into next weekend. The building high will push moisture associated with the weakening frontal boundary over the islands from the NE. With trade winds blowing, this moisture will favor windward areas, while the strong trades push some showers leeward on the smaller islands. Thus a windier and wetter trade wind pattern is expected from Thursday into next weekend.

In the meantime, the cold air advection of the past couple of days will end, and the air mass will gradually warm and moisten the next couple of days. However, a mid level ridge over the area will keep a strong lid on the island atmosphere, and keep shower chances rather low through Wednesday. With the trades blowing into tonight, a slight chance of night and morning showers will exist for windward areas. As winds weaken, there will be a slight chance of afternoon interior and leeward showers as sea breezes converge over the islands.

Aviation
Expect VFR conditions to prevail across the area thru 160400. Partial clearing expected from this large field of stable stratocu clouds /sc/ now covering the islands. Bases of these clds are btn 045 and 060 feet, well abv MVFR criteria. Also, brief spotty light rain or drizzle expected with tops running around 7k ft. The winds are down so no airmets expected thru at least 04Z.

Marine
The high surf advisory for exposed N and W facing shores has been cancelled, although surf along N facing shores will remain somewhat elevated this morning due to a slowly diminishing N swell. A couple of small WNW swells are possible Monday and Tuesday, with a moderate NNW swell possible from Wednesday into Friday. Resultant surf heights are expected to remain below advisory levels, with surf remaining below advisory levels along all shores through at least mid-week. Strong trade winds may cause wind waves to become large enough to warrant a high surf advisory for E facing shores later in the week.


Advisory and Warning Criteria
Location Advisory Warning
North-Facing Shores 15 Feet (8') 25 Feet
West-Facing Shores - Big Island 8 Feet (4'+) 12 Feet
West-Facing Shores - Remaining Islands 12 Feet (7') 20 Feet
South-Facing Shores 8 Feet (4'+) 15 Feet
East-Facing Shores 8 Feet (4'+) 15 Feet

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