Daily Weather

Oct 31, 2014 3:44 AM HST

Synopsis
Moisture from a dissipating front along with breezy trade winds will produce frequent showers today and tonight, especially across windward areas. Trade winds will gradually decrease during the weekend and into early next week. Showers will remain likely over windward areas, spilling into some leeward areas at times.

Discussion
Fast moving showers have continued to affect mainly windward sections of the state overnight. These showers have remained mostly low topped and of light to moderate intensity, which combined with the rapid motion has prevented any excessive rainfall amounts. Surface analysis depicts a dissipating front across the western end of the state, with a 1031 mb high centered about 1100 miles north of Honolulu. Fresh to strong trades prevail over the region to the south of this high. Water vapor imagery indicates an upper level low cutting off just south of the state, with some cumulonimbus developing during the last few hours over the offshore waters northeast of Maui, and within the region of favorable diffluence to the northeast of the upper low. Mimic-tpw imagery shows a narrow ribbon of enhanced moisture along the dissipating front lying across Kauai and Oahu. The 12Z soundings were quite moist and moderately unstable in the lower levels up to around 700 mb, but were very dry above.

For today, would expect frequent showers to continue across windward areas, with some of the showers spilling over into leeward sections of the smaller islands due to the brisk trade wind flow. It appears that the significantly dry airmass aloft will probably prevent deep convection from developing over the state, although heavier showers and a few thunderstorms will remain possible over the coastal and offshore waters to the northeast and east of Maui.

Trades will gradually weaken during the weekend as the surface high shifts northeast of the state and another cold front moves eastward north of 30°N. Lingering moisture from the nearby dissipated front and the proximity of the mid/upper level trough should keep showers active across windward areas, especially at night, with scattered showers continuing to spill into some leeward areas.

During the first half of next week, another strong surface high pushing eastward across the dateline will force the next frontal boundary slowly southeastward toward the state. Low level winds will veer slightly to the east-southeast in response, with some degree of enhanced moisture possibly being drawn up from the deep tropics over our area. Model consensus then dissipates the front just north of the state by next Thursday, as the surface high moves well north of the area. Trades should increase once again, with a typical windward shower pattern continuing.

Aviation
Moderate to locally strong trades across the islands early this morning will prevail at least through tonight. Thus the airmet for low level turb will continue. Much of the low clouds from a dissipating cold front are now staying along the north and northeast edge of the coastal waters. In fact, a few convection have developed along this line at this time, with CB tops fl350. Expect these activities to be limited to the aforementioned coastal waters areas, though low clouds from the band will spread to the islands at times, and providing some passing showers. Mainly VFR conditions will prevail across the sites, but then passing low clouds may lead to brief MVFR conditions, especially along windward and mountain areas. Early morning Lihue and Hilo soundings revealed drier conditions at the upper levels. Therefore the mention of light icing will be dropped at the next update.

Marine
A combination of north swell and trade driven wind waves continues to produce elevated surf on north and east facing shores. Another reinforcing north swell will arrive today, then slowly diminish through the weekend. A high surf advisory remains in effect through 6 am Saturday for east facing shores. Surf along south facing shores will remain small through Monday, with a slight bump Tuesday as a new long period swell arrives. Another small northwest swell will arrive Tuesday as well.

The overnight ascat pass missed most of the Hawaiian coastal waters, but interpolation from available data along with land based observations indicate that winds around 25 knots are likely continuing across many areas. A small craft advisory /sca/ remains posted through 6 am Saturday for most coastal areas due to the strong winds and large seas. Winds and seas should subside in some areas by Saturday, but SCA winds will likely continue across the typically windy areas around Maui county and the Big Island. The advisory has been extended for those zones through Saturday night.

Watches/Warnings/Advisories
High surf advisory until 6 am HST Saturday for east facing shores of Kauai Oahu Molokai Maui and Big Island.

Small craft advisory until 6 am HST Sunday for Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast waters.

Small craft advisory until 6 am HST Saturday for Kauai northwest waters, Kauai windward waters, Kauai leeward waters, Kauai channel, Oahu windward waters, Kaiwi Channel, Maui county windward waters.
All surf height observations and forecasts are for the full face surf height, from the trough to the crest of the wave.

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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