| Current Conditions | ||
| Temp |  | 4.1 C |
| RH | | 37 % |
| Wind | | ENE 0 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 404 FXHW60 PHFO 180602 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 802 PM HST Thu Sep 17 2020 .SYNOPSIS... The dry and stable trade wind pattern will continue into next week, with the best chance for showers developing overnight through the early morning periods across windward and mountain locations. Moderate trade winds may become locally breezy over the weekend, then relax by midweek as the ridge weakens to the north. && .DISCUSSION... Latest surface analysis and satellite imagery showed the subtropical ridge anchored north of the islands and patchy low- level clouds moving through from east to west. Water vapor imagery depicted mostly dry middle- to upper-level air over the state between an upper trough to the northwest and an upper ridge to the east and southeast. The afternoon upper-air soundings at Lihue and Hilo reflected this and exhibited mostly dry and stable profiles with PWs measured around 1.2 inches. Satellite-derived precipitable water (PW) imagery, however, does reveal a decent sized area of moisture skirting the islands to the south due to low pressure far south of the area in the deep tropics. Some upper-level debris clouds from the convection associated with this feature have made it as far north as the Big Island. Showers have been sparse with little accumulations over the past several days across the state. Guidance has initialized well with the current pattern and depicts the stable and dry trade wind conditions continuing through early next week as the upper heights rise over the weekend. Dewpoints reflect this dry pattern and dipped several degrees below predicted this afternoon, which drove relative humidities into the upper 30s to lower 40s for some leeward areas. Although a slight increase in moisture is possible as the aforementioned moisture skirts the islands to the south, showers will be sparse with the best chance occurring overnight through the early morning periods each day. Moderate trade winds may become locally breezy over the weekend, then relax by midweek in response to a weakness developing in the subtropical ridge as a front passes to the north. && .AVIATION... A surface ridge north of the islands will maintain moderate trade winds through early Friday morning. Expect mainly dry conditions also, with some low clouds and brief showers possible tonight over windward facing sections. This may produce brief periods of MVFR conditions along windward facing slopes, especially later tonight and early Friday morning. Otherwise, expect VFR conditions to prevail overnight. The trades are forecast to increase slightly on Friday, but mainly dry trade wind weather is expected to persist. Some windward sections may see some clouds and light showers from mid- morning through the afternoon on Friday. In addition, clouds and a chance of showers are possible along the upslope sections of the Leeward Big Island Friday afternoon. No AIRMETS are currently in effect, and none are expected through Friday afternoon. && .MARINE... Strengthening high pressure to the northeast of the islands has created a tight enough pressure gradient across the chain to support a Small Craft Advisory (SCA). The latest afternoon scatterometer pass showed 25 knot winds in the Alenuihaha Channel and over those waters south of the Big Island. The SCA is in effect for these waters, as well as Maalaea Bay and Pailolo Channel, as winds are expected reach SCA criteria and hold at those magnitudes through the weekend. Surf will remain below advisory levels along all shores. Longer period small south-southwest swells are expected to arrive over the next couple of days. North shore surf will remain nearly flat through tonight, then increase a bit as small north-northeast and northwest swells arrive Friday and last through early next week. East shore surf will increase a touch due to strengthened trade flow but will still stay below average through the middle of 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...Gibbs AVIATION...Houston MARINE...Blood Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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