Daily Weather


Dec 18, 2014 3:40 AM HST

Synopsis
High pressure centered north of the islands will maintain locally breezy trade winds through Friday. The trades will focus showers over windward and mountain areas. The winds will become light over the weekend as the high leaves the area and a front approaches the islands from the northwest. The front will move down the island chain between Sunday night and Tuesday night bringing with it some showery and windy weather.

Discussion
Differences remains between the two global models, the ECMWF /ec/ and GFS, regarding the upper level short wave trough and its support of the surface front early next week.

The most notable difference is in the timing of the upper level trough where the ec has the trough just west of Kauai Monday evening while the GFS has the trough over Kauai and Oahu.

The ec remains the stronger of the two with a cold 500 mb temp of minus 17 c. The GFS has a minus 14 c. Not much of a difference here where both temps are cold enough to support at least a slight chance of a thunderstorm and almost certain, spotty heavy showers.

The models differ thereafter. The ec keeps the upper trough over the islands Tuesday, thus maintaining a chance of enhanced showers and a slight chance of a thunderstorm. On the other hand, the GFS has the upper trough far NE of the islands, suggesting more light to moderate showers with the front. The two model do agree on the location of the front, over Maui Tuesday afternoon. Should we pursue the ec solution, improvement in the weather will come Tuesday night as the upper trough finally lifts out.

This is still a good few days away so we will wait and see if the models maintains a showery outlook for Monday and Monday night.

The models do also agree on a quiet weekend. The weather pattern may turn slightly convective with local daytime sea breezes as the trades eases to light to locally moderate. A strong and stable air mass will put a lid on these convective clouds. There will be enough of an easterly wind flow to carry a few shower bearing clouds to the windward areas of all the islands.

The pops and sky cover have been trimmed down for the windward and mountain areas of Molokai Maui and the Big Island this morning. It looks like it won't be that showery in these places this morning.

Aviation
High pressure to the north of the islands maintaining trade wind flow, with clouds and showers moving over mostly windward and mauka areas. Some MVFR conditions are expected with the clouds and showers in those areas. Otherwise VFR conditions are expected to prevail.

High pressure building to the north will strengthen trade winds today which may require an airmet for mechanical turbulence to the lee of the mountains.

Marine
A couple of zones have been added to the existing small craft advisory /sca/. These two zones are the windward waters of Kauai and Oahu and is due mainly to the building NW swell. The SCA for the affected zones is good till 6 pm HST Friday.

We do look forward to the SCA being lower late Friday afternoon. This will be short live however. The SCA will likely be hoisted Saturday night for the anticipated large NW swell.

We will be keeping a close watch to this new NW swell. Surf heights are expected to rise to near or at advisory levels for the north and west shores of some islands tonight. So, an advisory may be needed later this morning. This swell just hit buoy 51001 a couple of hours ago. It will peak tonight and gradually lower Friday.

The upcoming large NW swell will likely need a high surf warning involving both north and west facing shores of most islands. The source of this swell is from a rather broad storm low currently located off the east coast of Japan. Another storm low is predicted by the models to form north of the islands the middle of next week which may keep surf elevated in at least the advisory range through Christmas.

Watches/Warnings/Advisories
Small craft advisory until 600 pm HST Friday for windward waters of Kauai and Oahu, Maalaea Bay, the waters south of the Big Island, and the Pailolo and Alenuihaha channels.







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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