| Current Conditions | ||
| Temp |  | 4.7 C |
| RH | | 9 % |
| Wind | | NE 15 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 566 FXHW60 PHFO 181950 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 950 AM HST Thu Apr 18 2019 .SYNOPSIS... Moderate to locally breezy trade winds will prevail through much of the week as surface high pressure holds north of the state. Rather stable conditions will remain in place, leading to a typical pattern of mainly windward and mauka showers. && .DISCUSSION... A stable and moderate to locally breezy trade wind flow is place across most of the state. The trades are being driven by a 1027 mb high passing about 1,100 miles north of the state. A mid level ridge is building over the islands from the west, pushing a weak mid level trough a couple hundred miles east of the Big Island. This is causing the inversion to be slightly higher and weaker over the eastern end of the state, with the overnight soundings from Hilo and Lihue showing the inversion near 8,500 ft and 6,000 ft, respectively. As a result, a small pocket of moisture is producing active showers over windward Big Island, while modest rainfall has been confined to windward terrain elsewhere. Expect showers to decrease on windward Big Island this afternoon, as spotty showers develop over the Kona slopes. Elsewhere, little change is expected today. Overall, a typical trade wind weather pattern is expected through the upcoming week. The surface high will settle to the northeast of the state, while its associated surface stalls about 300 to 500 miles north of the islands. We could see an uptick in trade winds during the weekend as the ridge briefly strengthens. Stable conditions will dominate through much of the week as the mid level ridge will be parked overhead. Generally, precipitable water will be near normal, suggesting that showers will be modest and confined to windward slopes. As random pockets of low level moisture move through on the trade wind flow, expect brief and localized increases in showers. Aside from afternoon showers on the Kona slopes of the Big Island, leeward areas will be mostly dry. && .AVIATION... Strong high pressure far north of the islands will support a locally brisk trade wind pattern through twenty-four hours and beyond. Clouds and showers will continue to favor windward slopes and coasts of all islands. The air mass over the eastern third of the state is expected to become mildly unstable this afternoon. Sea breeze driven cumulus development across leeward and interior Big Island could produce brief heavy downpours this afternoon and early evening. Elsewhere, the air mass will remain mostly dry and mostly stable. Shower activity across the smaller islands is expected to remain light and patchy. Trade winds will continue to strengthen as the day progresses. AIRMET Tango, already in effect for mechanical turbulence below 8k feet, will continue until further notice, possibly for several days. && .MARINE... Fresh to strong easterly trade winds associated with a strengthening ridge north of the islands will fill in today and continue through early next week. A Small Craft Advisory is in effect for the Pailolo and Alenuihaha channels, Maalaea Bay, and over the waters around South Point of the Big Island through Sunday where the strong winds are expected. Surf along north and west facing shores will remain small today, then rise tonight into Friday as a new north-northwest (320-340 deg) swell builds down the island chain. This source will be from a gale that was centered over the Aleutians near the Date Line Sunday that quickly tracked south-southeast and weakened Monday through Tuesday. After the peak on Friday, the swell will quickly ease Friday night into the weekend. A small westerly swell from a compact gale that has developed east of Japan will be possible early next week. Surf along south facing shores will remain small through the weekend with mainly background south-southwest pulses moving through. An upward trend is anticipated early next week, beginning as early as Sunday night due to activity south to southeast of New Zealand over the past few days. Guidance depicts this source peaking at Pago Pago Saturday, which should correlate to above average south shore surf continuing into midweek. Surf along east facing shores will remain small today, then slightly come up Friday through the weekend due to fresh trades locally and just upstream. Expect this trend to continue early next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Bedal MARINE...Foster Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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