| Current Conditions | ||
| Temp |  | 2.2 C |
| RH | | 70 % |
| Wind | | S 1 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 310 FXHW60 PHFO 211339 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 339 AM HST Thu Sep 21 2017 .SYNOPSIS... The moderate to locally strong trades will be turning slightly softer this evening as the surface high weakens far NNE of the islands. Gentler trade winds will prevail through early next week with clouds and showers favoring the windward and mauka areas. The showers will be most frequent during the nights and mornings. && .DISCUSSION... The locally strong trades will be trending slightly softer this evening as the surface of 1032 mb starts weakening while drifting east, further away from the islands. The focus will change from the high to its associated ridge currently located 800 miles north of Kauai. This ridge will move south over the weekend to about 360 miles N of Kauai by early Tuesday morning. Moderate trade winds will rule the region during this stretch, and is expected to be strong enough to ward off or limit the daytime sea breezes. The upper low located 700 miles NE of the Big Island this morning, is forecast to remain stationary there through early next week. The low may have deepened the marine layer to its current 16k feet over the Big Island, but it has not really affected the islands negatively. And none is expected as long it does not come any closer to the islands. In fact, mid level ridging briefly builds over the Big Island Saturday night, but weakens by Saturday afternoon. Therefore, clouds will continue its presence over the Big Island summits on a daily afternoon bases through early next week. The GFS has now picked up on the mid layer moisture between 15k and 20k feet over the Big island. The overcast patch which covered the Big Island on last evening's satellite imagery, has pretty much broken up, but there is more of it just south of South Point, and can easily surge up over the Big Island at any time. A short wave trough now approaching the Big Island from the N should keep these clouds at bay or even disperse it as the day progresses. Precipitable water content is relatively moderate at best this morning, at between 1.2 and 1.6 inches, Lihue and Hilo, respectively, with the highest amount over the Big Island. Little change is expected through early next week with no additional influx. Satellite imagery shows an area of broken low clouds with embedded showers approaching the central islands. They will be affecting Molokai and Maui first by 4 am, and Oahu between the 7 am and 9 am. The area is breaking up as it near these islands. These clouds will bring a period of passing showers lasting a couple of hours. A field of scattered low clouds will continue to push through Kauai through the rest of the morning hours. The windward and mountain areas will absorb most of these showers. More clouds and showers appear headed for the Hamakua coast, likely making a showery day there. .AVIATION... High pressure north-northeast of the State will continue to drive a moderate to breezy trade wind flow across the islands through tonight. Clouds and showers will favor windward and mauka areas, with a stray shower reaching leeward locales from time to time. Predominantly VFR conditions are expected at the terminals through 12Z Friday, but some brief MVFR cigs/vsbys will be possible in windward areas as trade showers move through. AIRMET Tango remains in effect for low level turbulence over and downwind of the terrain of all islands. The AIRMET will likely continue through the day on today. AIRMET Sierra may be needed for mountain obscuration across portions of the island chain later this morning. && .MARINE... Fresh to locally strong trades associated with 1032 mb high pressure north-northeast of the state across the eastern Pacific will hold through this afternoon before trending down over the upcoming weekend and early next week. Strongest winds are expected across the Pailolo and Alenuihaha Channels, Maalaea Bay and the waters south of the Big Island through this time. Trades should reach the light to moderate range by the end of the weekend as high pressure shifts eastward and weakens in response to a frontal boundary passing far north of the state. This pattern should hold through the first half of the upcoming week (potential for land/sea breezes for some leeward areas setting up Monday through Tuesday). A combination of moderate to strong breezes locally and upstream of the islands south of high pressure will continue to generate rough surf along east facing shores into Friday. Surf along east facing shores will trend down over the upcoming weekend as the trades weaken locally and upstream. Guidance suggests a weak or broad surface trough developing east of the islands Friday due to a broad upper low centered northeast of the state, which will weaken the easterlies upstream of the state and lower the trade wind swell. Surf along south facing shores will remain small through early next week with mainly background southeast and southwest swell energy expected. The next potential long-period pulse out of the southwest from the Tasman Sea will be possible by Sunday, which should lead to a slight increase in surf. For the extended, strong- to gale-force southwest winds associated with a low that has been impacting the Tasman Sea over the past 24 hrs may lead to another small southwest (210-220 deg) swell Tuesday through midweek. A small northwest (310 deg) swell associated with broad and complex low pressure that has been centered over the central Pacific near the Date Line over the past couple of days is expected to fill in locally Thursday and hold into the weekend before easing. The latest surface analysis showed 989 mb low centered near the Aleutians around the Date Line with a decent pocket of strong- to near gale- force winds focused within the 320 to 330 deg band relative to the islands. This may end up reinforcing what is left of this weekend's 310 deg energy by Monday, before completely fading Tuesday through Wednesday. As a result, a slight increase in surf is expected along north and west facing shores beginning Thursday, which should hold into early next week before dropping off. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo and Alenuihaha Channels, and waters south of the Big Island. && $$ Lau/Jelsema/Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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