| Current Conditions | ||
| Temp |  | 2.4 C |
| RH | | 99 % |
| Wind | | NNE 29 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 672 FXHW60 PHFO 181331 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 331 AM HST Mon Jun 18 2018 .SYNOPSIS... A weak ridge will remain north of the state for the next few days as a weak cold front pushes south towards the state. High clouds ahead of this system are already moving over the islands. This front will produce mainly clouds as the atmospheric lift associated with this system will remain north of the islands. Wind directions shift from Tuesday night into Wednesday becoming east to southeast potentially pushing the VOG plume from the Big Island northwestward across the smaller Hawaiian Islands. Trade winds will increase to moderate levels from Friday into the weekend blowing out any lingering VOG over the smaller islands. && .DISCUSSION... An unusual weather pattern for this time of year has formed across the Central Pacific basin. A weak high pressure surface ridge will remain north of the state for the next few days producing light trade winds with daytime sea breezes mainly along western slopes of all islands. In the upper levels just east of the islands a high and low center couplet sets up along 140W longitude. Much of the shower activity over the islands for the next several days will be driven by mesoscale (smaller scale) convergence boundaries. For Today, high cirrus clouds are drifting over the state from the north. Light trade winds and daytime sea breezes along western slopes of all islands will build low clouds and isolated to scattered showers along windward, mountain and interior sections of each island. Shower activity will be limited by a low trade wind inversion heights around 5,000 feet in a relatively stable atmosphere. On Tuesday and Wednesday, a diminishing cold front will drive south through the ridge towards the state. The best low level convergence associated with this boundary will stall to the north keeping enhanced shower activity north of the islands. The main impact with this system will be periods of clouds through Wednesday. Shower activity will be limited from isolated to scattered in a relatively stable environment. Light trade winds shift also directions from Tuesday night into Wednesday becoming east to southeast pushing the northern edge of the VOG (Volcanic smOG) plume northwestward from the Big Island across the smaller Hawaiian Islands with VOG lingering across most of the state through Thursday. A building ridge north of the islands will increase the trade winds to moderate levels from Friday onward blowing out any lingering VOG over the smaller islands. Returning moderate trade winds on Friday will produce increasing cloud and shower trends favoring more typical windward and mountain areas of each island. An upper level low will also track north of the islands helping to lift the cap on the trade wind inversion and enhance shower coverage across the Hawaiian Islands through the weekend with periods of showers potentially drifting over leeward areas. The track of this low remains highly variable this far out and enough differences remain between the American (GFS) model and the European (ECMWF) model for only moderate confidence in the long range precipitation forecast for now. Stay tuned for updates. && .AVIATION... Surface ridge persisting just north of the islands should keep trade winds light today, with early morning land breezes giving ways to afternoon sea breezes. Anticipate VFR conditions for much of the state today, though the on-going volcanic emissions on the Big Island will bring areas of MVFR VIS HZ to that island. No AIRMETs are expected. && .MARINE... A surface ridge just N of Kauai will move little today, and then drift S and weaken as a dissipating front approaches from the N tonight and Tuesday. The front is expected to stall N of Kauai, develop into a trough, and then gradually dissipate through Wednesday as it moves NW. Light to locally moderate NE to E trade winds today will likely weaken by Tuesday, with winds potentially becoming more variable through Wednesday as the large scale flow becomes quite weak. High pressure will consolidate far NE of the area Thursday and Friday, and then move W into next weekend, supporting increasing trade winds. Winds will likely be strong enough to warrant a Small Craft Advisory in the windier zones on Thursday or Friday. The long-period WNW and S swells of the past couple of days will diminish through Tuesday, with little significant swell expected for most of the upcoming week. Small, long-period SSW swells will likely support tiny to small surf along S facing shores, while locally strong trade winds at the end of the week will lead to increased short-period E swell. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Bohlin AVIATION...Hui MARINE...Birchard Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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