176 FXHW60 PHFO 270636 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 836 PM HST Thu Dec 26 2019 .SYNOPSIS... A dissipating front will maintain wet conditions over portions of the Big Island tonight. Northerly winds will build down the rest of the island chain tonight with showers favoring north slopes of Kauai and Oahu. Showers will favor windward slopes of all islands as locally breezy trade winds develop statewide on Friday, then shift out of the east during the weekend. Trade winds will decrease on Wednesday. && .DISCUSSION... A dissipating front near the Big Island is bringing moderate to briefly heavy showers to mainly Kau and Puna Districts, while post frontal flow is carrying scattered showers over the rest of the state. The front will move slowly southeast and dissipate tonight and current southerly winds near the Big Island will shift from the northeast by morning. The rest of the state will see increasing northerly winds tonight turning from the northeast by morning. A high pressure centered far northwest of the state will push eastward overnight, increasing the pressure gradient of the state thereby increasing the northeast trade winds. Winds will be breezy Friday over the smaller islands as the high moves closer to the state, and turn easterly over the weekend. Radar across the state show progressively shrinking cloud tops from east to west with tops reaching 25 kft near the Big Island, 14 kft near Maui, 10 kft close to Oahu, and 6 kft near Kauai. The shrinking cloud tops indicated strengthening stability moving in from the northwest in the airmass behind the front. Thursday afternoon sounding showed a strong temperature inversion of 5 degrees F at 6 thousand feet over Lihue, while the Hilo sounding showed no inversion with moderate amounts instability available to any growing cloud tops. The stable airmass will continue an eastward motion overnight and push the heavier showers and higher cloud tops east of the Big Island by Friday morning. A more typical trade wind pattern is in store Friday with northeasterly trade winds and showers focusing over windward and mountain areas. The winds will likely be breezy and gusty over the western end of the island chain, where a shallow band of moisture will enhance windward rainfall. Lingering moisture from the stalled front is expected to maintain wet conditions across windward Big Island. Leeward locations on the smaller islands will experience partly cloudy skies with passing brief showers most likely during the time from the late afternoon through early morning hours. The leeward Big Island will see the usually diurnal pattern of mostly clear skies overnight lasting into the morning hours before sea breezes bring afternoon clouds and isolated showers. Over the weekend, showers coverage will decrease as an upper ridge brings stable conditions while breezy easterly trade winds continue. By Monday, the high will be located far northeast of the state with a cold front far northwest of Kauai. This scenario will continue the breezy east trade winds from Oahu to the Big Island, but may turn winds from the east southeasterly direction around Kauai. The front will gradually approach through midweek, turning winds lighter and shifted from the east southeast across the state. The front may eventually reach Kauai by Thursday morning bringing an increase in clouds and showers to the Garden Island. && .AVIATION... A high pressure system building in north of the state will change the wind directions overnight from north northwest to northeast trade winds by Friday morning for most islands. A cloud band lingers over the windward slopes of the Big Island, this band will keep periods of low ceilings and showers in the forecast along the Hilo side of the Big Island over the next 24 hours. Passing showers will tend to favor north and east slopes of all islands as the trade winds return. Low cloud ceilings are possible along windward and mountain slopes with brief periods of Tempo Mountain Obscurations. An AIRMET for low level Tempo Moderate Turbulence will likely be issued by Friday afternoon for breezy trade winds over the western islands of Kauai and Oahu. && .MARINE... A front will linger around the Big Island into tonight, then fade by Friday. High pressure will build north of the state tonight and steadily move east through the weekend. Moderate to fresh northerly winds are expected to fill in tonight especially around Kauai and Oahu and gradually spread east. Strong northeasterly trades will return on Friday and gradually veer towards the east over the next few days. Currently, no marine warnings are in effect, however, trade winds are expected to increase to Small Craft Advisory speeds by Friday and likely continue through the weekend. Small Craft Advisory's will likely be posted for Friday for waters around Kauai and possibly the windier waters around Maui County and the Big Island. Coastal flooding will remain possible over low lying areas for the next couple of mornings due to higher than normal water levels and large astronomical tides. However, subsequent high tides will gradually lower heading into the weekend, with impacts decreasing as well. A series of small northwest swells will support small surf along exposed shores through Friday. An upward trend this weekend could support moderate surf by Sunday, but likely below advisory level. Guidance is still advertising a hurricane-force low developing east of Japan this weekend which could translate to a very large northwest swell arriving locally early next week. This swell will likely result in warning level surf for north and west facing shores Monday into Tuesday. A small, long-period southwest swell is expected to arrive this weekend and could provide some small surf along south facing shores. No other significant swells are expected. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Morrison AVIATION...Bohlin MARINE...Kino