Daily WeatherNov 26, 2014 3:29 AM HST
Moderate to fresh trade winds and dry conditions will prevail across most of the state today, but lingering low level moisture will continue to generate showers across the windward Big Island. A strong high pressure system will settle north of the islands starting tonight, resulting in breezier trades for the rest of the week and into the weekend. A stable air mass will keep trade showers mostly light and confined to the windward and mauka areas.
Clouds have remained abundant across windward sections of the state overnight. The smaller islands have been largely dry, except for some persistent showers along the windward slopes of Haleakala. However the windward Big Island has remained soupy with widespread measurable rainfall continuing. At the surface, a 1022 mb high is centered about 500 miles northwest of Kauai, with a cold front along 30°N separating this high from a larger 1026 mb high about 1250 miles northwest of Kauai. The 12Z Hilo sounding found abundant low level moisture beneath an elevated inversion around 9000 feet. Meanwhile the Lihue sounding shows a strong inversion based around 5500 feet, and a very dry atmosphere with pwat of only 0.77 inches, which is about two standard deviations below normal.
The stubborn low level trough which has lingered near Maui county for the past couple of days should finally wash out later today, allowing for less cloudiness across windward areas. Most of the state will remain dry due to the strong/low inversion and lack of available moisture, but scattered showers will remain across the windward Big Island where deeper moisture is available.
A stronger surface high is then forecast to build slowly eastward to the north of the state between 30°N and 40°N from tonight 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. We may see a modest increase in windward showers on Friday, when the remnants of an old frontal boundary reach the state. Blended model data keeps pwats around one inch, which is below the 25th percentile for this time of year, through the next several days. Therefore would expect rainfall amounts to remain mostly on the light side even over windward areas. Long range models do not show any indications of a frontal passage across the main Hawaiian islands through the weekend, with some potential for another weak front to approach the state next Tuesday or Wednesday.
With low level winds from the northeast, low clouds, some with accompanying light rain or showers, are mainly concentrated over north clockwise through east sections of the isles. This is where MVFR conditions may be occurring from time to time. On the Big Island, though, MVFR has been more persistent, from Upolu Point to Volcano. Elsewhere, VFR is the rule.
An airmet for mountain obscuration remains in effect for the northeast quadrant of the Big Island. An airmet for low level turbulence, south through west of the mountains, will be posted at 0600 HST as trade winds ramp up.
Northwest swell has continued to subside overnight at both buoy 51101 and Waimea bay. The high surf advisory for north and west facing shores will be dropped as scheduled with the morning forecast package.
A new NNE swell, generated by a gale low 1400 miles north northeast of Oahu, is due to arrive in the islands starting this afternoon and peaking tonight. This swell combined with building wind waves due to increasing trade winds will cause rough surf to develop on east facing shores, especially those with a northern exposure. Near advisory level surf may occur across some of the east facing shores tonight into early Thursday. Surf will be increasing across north facing shores as well, but is currently expected to remain just below advisory levels there. This swell will also cause a concern for harbor surges into Kahului and Hilo harbors tonight into Thursday.
The overnight ascat pass found substantial areas of 25 knot winds in the Alenuihaha channel and southeast/south of the Big Island, with a small area of near 30 knot winds west of Upolu Point. A small craft advisory /sca/ will remain posted for most of the marine zones due to strong winds in the typically windy areas around Maui county and the Big Island, and a combination of wind waves and nw/n swells pushing combined seas to 10 feet. Sca conditions are likely to remain widespread across the Hawaiian coastal waters from tonight through the remainder of this week as strong trade winds continue.
Small craft advisory until 6 am HST Thursday for Kauai northwest waters, Kauai windward waters, Kauai channel, Oahu windward waters, Kaiwi Channel, Maui county windward waters, Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast 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