Daily Weather

Nov 25, 2014 7:00 AM HST

Update
The forecast package has been updated for some adjustments to especially the windward districts of Maui county and the Big Island for today and tonight where the cloud cover and pops were increased.

Synopsis
High pressure will move north of the state today through Wednesday, bringing fresh trade winds along with cooler and drier conditions. Another stronger high pressure cell will build north of the state from Thursday into the weekend, with fresh to strong trade winds prevailing over the islands, and showers focused mainly across windward and mauka areas.

Discussion
Radar detects very little shower activity across the state, however rain gauges and surface obs show that some windward areas have continued to receive measurable rainfall during the night. This activity is very shallow and mostly not being seen by radar, as low level moisture is pushed against the island terrain by north/northeast winds. The front which passed through the islands on Monday now appears to have dissipated south of the Big Island, but considerable stratocu continues to linger across the state. At the surface, a 1021 mb high is centered about 700 miles northwest of Kauai and is building to the north of the state behind the front. Aloft, a deep mid/upper trough is lifting to the north and east along 150°W, with an upstream ridge building east of the international dateline. The 12Z soundings show low level moisture and northerly flow beneath strengthening inversions based between 6000 and 7500 feet. Pwats ranged from 1.17 inches at Hilo to a very dry 0.87 inches at Lihue. Mimic-tpw satellite imagery shows an even drier airmass spreading southward into the western and central parts of the state.

Low level flow will veer to the northeast today, as surface high pressure moves north of the state. Lingering windward shower activity should mostly end by this afternoon across the smaller islands as the airmass dries out even more and the inversion continues to lower. Slightly deeper moisture will probably linger across the windward Big Island, where isolated/scattered light showers will remain possible through the day.

A quick moving cold front passing well north of the area will cause trade winds to slacken a bit across the state tonight into Wednesday, although locally breezy conditions will still likely exist. A stronger surface high is then forecast to build slowly eastward to the north of the state between 30°N and 40°N from Wednesday night into the weekend. Breezy conditions will become more widespread over land areas during this time as fresh to strong trade winds prevail. Showers will be mainly confined to windward and mauka areas through the period, and most common during the night and early morning hours. Blended model data keeps pwats at or slightly below 1 inch through Wednesday, with a slight recovery of low level moisture thereafter. Model pwats remain near or below the 25th percentile for this time of year through the next several days, so would expect rainfall amounts to remain mostly on the light side even over windward areas. Long range models do not show any indications of another frontal passage across the main Hawaiian islands through early next week.

Aviation
Quite a bit of low clouds lingering in the island vicinity will continue to affect the area this morning, especially for north and east. There are some lower bases low clouds embedded in the cloud field. Expect VFR condition should prevail over much of the site, though windward sites may experience brief MVFR ceiling condition. Air mass is rather dry and stable so precipitation, if any, will be light.

Gusty north winds will become moderate northeast trade winds across the islands later today as a surface high pressure ridge builds north of the islands. Believe winds may not be strong enough to bring low level turb affecting imt S thru W areas of the mtns at this time, though the possibility still exists.

Marine
The overnight ascat pass missed most of the Hawaiian coastal waters, but did estimate winds near 20 knots around Kauai. Fresh to locally strong northeast winds combined with a lingering north-northwest swell will bring small craft advisory /sca/ conditions to most of the marine zones through today. This swell will subside tonight and Wednesday, but fresh to locally strong trade winds will likely maintain SCA conditions across the normally windy zones around Maui county and the Big Island. A stronger high building north of the state should increase trade winds further from Wednesday night through the end of the week, with SCA conditions forecast to spread across the kaiwi and Kauai channels as well.

Seas continue to run near 10 feet at Waimea bay buoy and 12 feet at buoy 51101, although the wave energy is spread across a broad spectrum with some short period wind waves mixed in. Wavewatch data indicates that the current north-northwest swell will remain high enough to likely maintain advisory level surf through today across north facing shores of all smaller islands, and for west facing shores of Kauai county. This swell will subside tonight into Wednesday. A new north-northeast swell is expected to arrive Wednesday night into Thursday, and combined with wind driven short-period northeast/east swell could push surf near or above advisory levels across some east facing shores. Choppy surf conditions due to strong trade winds appear likely to continue on east facing shores into the weekend.

Watches/Warnings/Advisories
High surf advisory until 6 pm HST this evening for north and west facing shores of Niihau and Kauai and for north facing shores of Oahu Molokai and Maui.

Small craft advisory until 6 pm HST Wednesday for Kaiwi Channel, Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast waters.

Small craft advisory until 6 pm HST this evening for Kauai northwest waters, Kauai windward waters, Kauai leeward waters, Kauai channel, Oahu windward waters, Maui county windward waters, Big Island windward waters.








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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