| Current Conditions | ||
| Temp |  | -0.2 C |
| RH | | 40 % |
| Wind | | NNE 31 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 177 FXHW60 PHFO 151340 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 340 AM HST Sat Dec 15 2018 .SYNOPSIS... Mostly dry and pleasant weather can be expected over the weekend thanks to a stable trade wind air mass. Winds will gradually diminish over the weekend and on into early next week as the ridge of high pressure weakens, due to a front approaching the islands. The front is expected to move down the island chain from late Tuesday through Wednesday with showers increasing with its passage. Cooler and breezy weather will fill in behind the front. && .DISCUSSION... Satellite imagery shows a broken low cloud layer made up of a stable stratocumulus deck, spaced out across the windward waters. Showers, if any, are of the light, drizzle variety. They are moving from east to west with a moderate to locally strong trade wind flow. Some changes were made to the grids overnight, primarily drying out the trade wind showers to isolated for all islands' windward and mountain sectors, through Sunday night. The morning soundings from Lihue and Hilo showed a strong low level inversion with a base at around 5k feet. Precipitable water ranged from 0.77 to 0.93 of an inch, which is quite dry. A 1024 mb surface high lies 560 miles NW of Kauai, with a ridge extending to 320 miles N of Oahu this morning. The two combined to sustained a constant flow of trade winds to the islands at moderate to locally strong speeds. The center of this high is expected to pass directly N of the islands on Sunday with a 1022 mb center. It is not a very strong high, but it will be strong enough to maintain locally strong trades to the sensitive near- shore areas of Maui County and waters south of the Big Island. Please refer to marine section below for more details. The strength of the trades will dip to moderate speed by Monday night while the front continues on its eastward push toward the islands. The front is expected to reach Kauai Tuesday afternoon, then proceed down the island chain through Tuesday night, finally pushing east of the Big Island by Wednesday evening. The front is expected to have a some scattered to numerous showers, heavily favoring the windward and mountain areas. These showers won't have much depth, only to 8 to 10k feet. But they can have some very low visibilites. Scattered light trade wind showers continues behind the front, lasting through most of Wednesday before drying out. Along with these showers, is a cool air mass, where we expect highs on Wednesday to be in the mid to upper 70s. Wednesday night's minimum temps are expected to be only in the 60s. The NE trade winds will turn more easterly on Thursday and Friday, resulting in slightly warmer temps. && .AVIATION... A deep-layer ridge centered N of the islands will change little through tonight, with stable trade wind weather prevailing. The moderate to locally fresh ENE trade winds will deliver stable low clouds that will favor windward areas, and a strong subsidence inversion based near 5000 feet will keep rainfall chances quite low. While brief and isolated MVFR ceilings may occur, VFR conditions will prevail statewide. AIRMET Tango for low-level turbulence to the S and W of the mountains will remain posted today, but may be cancelled tonight or Sunday as trade winds ease slightly. && .MARINE... Trade winds have remained elevated for the typically windier areas near Maui and the Big Island, so the Small Craft Advisory (SCA) continues for those zones. A large, long-period northwest swell will arrive late in the day and rise rapidly. A High Surf Warning (HSW) will be posted to account for this episode. It is expected to peak Sunday, and then subside some on Monday. An even larger northwest swell will build late Monday, peaking well above warning levels. Exposed coastal waters will once again rise to over 10 feet as these swells come rolling through. Expect the current SCA to once again be expanded to most, if not all, the coastal waters for the first half of the new week as the new swells arrive. See the latest Oahu Surf Discussion (SRDHFO) for additional details on surf and swell. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Warning from 4 PM this afternoon to 6 AM HST Monday for the north and west facing shores of Niihau, Kauai, Oahu, and Molokai, and north facing shores of Maui. Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo and Alenuihaha Channels, and waters south of the Big Island. && $$ H Lau/Birchard/Kinel Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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