Thursday, August 21, 2014 596-SURF , 596-WAVE , 922-BONG , 638-RUSH , 572-SURF(MAUI) , 241-SURF (KAUAI) , 324-RUSH (BIG ISLAND)
   
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Winds Statewide in a glance ...go HERE (this link is also the 4th drop down under weather)

Aug 15, 2014 3:39 AM HST

Synopsis
Locally breezy trade winds will continue through the weekend. Clouds and showers will be focused over windward and mauka areas, mainly during the night and morning hours. Isolated showers will also be possible across the leeward slopes of the Big Island each afternoon and evening.

Discussion
Stable stratocumulus clouds and scattered low-topped showers have increased across the windward coastal waters during the last several hours, but rain gauge data indicates that only light rainfall amounts have occurred at some land stations, with most places remaining dry. Surface analysis depicts a high pressure ridge nosing westward along 26°N, between Hawaii and weakening tropical storm Julio far to our north. The building high to our north has caused moderate trade winds to resume across the state. Aloft, a mid/upper level anticyclone is centered to the northeast of the state with a ridge extending westward to our north. The 12Z soundings found a dry and stable environment remaining in place, with a well defined inversion lowering to about 5500 feet at Lihue. It appears that the Hilo sounding was probably affected by nearby showers, which resulted in a slightly higher inversion up near 8000 feet along with a slight pwat increase. Pwats at both stations remained below the 25th percentile for this time of year. Mimic-tpw imagery shows little change in the airmass upstream of the state, with estimated pwats near or just over one inch extending eastward for over 1000 miles, and the northern edge of deep tropical moisture remaining a few hundred miles south of the Big Island.

Little change is in store for today through the weekend, with moderate to locally breezy trades continuing. Ridging aloft will remain over and north of the state. Models maintain dry and stable conditions, with the inversion remaining at 5-6k feet, and pwats remaining below normal, near or just over one inch. Expect the rather dry trade pattern to persist, with limited passing showers mainly during the late night and early morning over windward and mauka areas, and isolated showers possible on the leeward Big Island each afternoon and early evening.

A somewhat wetter trade pattern may develop early next week, when most of the model guidance develops a weak mid/upper level trough near or just north of the state. This should allow for some weakening of the subsidence inversion, which combined with pockets of modestly higher moisture moving through in the continued moderate trade wind flow could allow for increased shower activity. Would expect showers to remain focused over windward/mauka, but leeward areas could see a bit more shower activity as well especially during the late night and early morning hours.

There continues to be much uncertainty with respect to potential developments in the tropical Pacific as we head into next week. Global models have been consistently indicating some sort of development far southeast of the state, but also have been depicting wildly varying evolutions and motions of any system that may eventually develop. The situation is further complicated by the potential for interaction with current east Pacific tropical storm Karina. It is too early to have any confidence as to the potential impacts, if any, on island weather next week. For now, the forecast calls for typical trade wind weather to continue.

Marine
The overnight ascat pass missed the Hawaiian coastal waters, but an earlier pass from late Thursday morning indicated a pocket of 25 knot winds in the Alenuihaha channel. Trade winds are expected to gradually strengthen further today through the weekend, and a small craft advisory remains in effect for the typically windier areas near Maui and the Big Island. Winds around 25 knots are expected to continue across the advisory area through the weekend.

Swell from a variety of sources will continue to affect the state through the weekend, but resulting surf heights are expected to remain below advisory criteria on all shores. A small northwest swell will arrive today and continue through the weekend, while several overlapping small southerly swells will continue to arrive through the weekend and into next week.

Watches/Warnings/Advisories
Small craft advisory until 6 am HST Monday for Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast waters.

 

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